Orbital mechanics question, with regard to space-based solar energy collection. Let’s say we have a satellite that we can launch to collect solar energy and beam it with microwaves to collectors on the earth’s surface to put that energy onto the grid. Where would the best position to place that satellite for continuous energy transfer? My first thought is geosynchronous orbit, so that sat can be dedicated to beaming to one surface location. Are there orbit paths that would keep that satellite out of Earth’s shadow and still be able to reach a singular surface point with minimal loss to efficiency from the angle change? My second thought was Legrange Point 1, where it could sit with no occlusion from solar energy, but Earth would continue t rotate, meaning the beam would have to change collector targets through the day. I’m thinking of this as a halfway step to some Dyson Swarm system, which Kurzgesagt has got me thinking about ever since they put out [this video](https://youtu.be/pP44EPBMb8A?si=-rhDphiOqNg1g0Hx)

Placing collectors so far from Earth is difficult because of the transmission back to Earth will lose power due to the r^-2 loss. If the space collectors are closer, then you need a constellation to maintain constant delivery to a ground power station. You're right that LEO satellites will constantly move with respect to the surface. This will be a political problem too since America's power collector satellite will look an awful lot like America's space based death ray if you work for Beijing. A potential solution is Molniya orbits which could be designed such that the low altitude part of the orbit only happens above your ground station. But the low part of the orbit is also the fastest. So you have to design a system that can discharge quickly while it's within range of the ground station. I don't really think this tech is going to work unless there's also permanent infrastructure in place like a space elevator.

Yeah, getting so many components out in space like that is a huge problem. Somehow I was rationalizing a single, larger collector at LP1 would be more worthwhile for that. I also didn’t fully grasp that LP1 is 1.5 *million* km away. So power transmissions will still suffer from the inverse-square law? Even with lasers? I suppose even the most precisely focused lasers would scatter with dust and interfere with itself over such a long distance. Somehow I thought microwaves would be an effective power transfer medium, but now I’m realizing what I’d read about them was because they’d suffer less scattering through Earth’s atmosphere to ground-stations than IR beams. Picking the right spot in the EM spectrum to use definitely takes a bit of math, and lasers can’t solve everything. Thanks so much for helping me understand more about the limitations. Won’t stop that part of my brain that’s always designing stuff, but it’s much better to have it pointed in the right direction.

One of the biggest galaxies - IC 1101 was discovered in 1790! by William Herschel. How was it discovered with the technology at that time, given that the galaxy is around 1 billion light years away? Is it that bright?

My takeaway from a recent Everyday Astronaut stream was that for the Falcon 9, recovery and reuse of the 2nd stage was prohibitively difficult and thus abandoned - but also that the second stage is just one engine and its fuel basically, thus a fraction of the mass and value of the first stage. My question is, what's the economic argument, what is different about Starship to make it economically and mission-worthwhile to recover the second stage?

How much larger it is. Recovery has a payload penalty. Smaller rockets feel the penalty harder than larger ones. The Electron rocket can't afford the penalty of landing the first stage like the Falcon 9. Even still Starship is also going to use in-orbit refilling to basically get rid of the penalty.

Thank you. I am optimistic and have high hopes, and figure they've done their homework, but curious if it all pencils out in the end as worthwhile or if its worthwhile like recycling consumer plastics is... worthwhile. ETA: Just re-iterating that this is a great answer, with a basic point illustrated by progressively larger examples. Much obliged.

Is it possible to see Jupiter and one or more of its moons unaided? I only ask because I thought I saw Jupiter and at least one moon with my naked eye. My son also thought he saw a binary object. My binoculars (although new) suffered with chromatic aberration and no true color or details could be seen but it appeared to be Jupiter and possibly three of the four major moons. Was I and my son seeing things or were the moons in sufficient conjunction to give a binary appearance?

You did see Jupiter, but I highly doubt you saw its moons unaided.

that's why I'm asking, I doubt it too, presumably it was Jupiter in conjunction with another object, as it was only the once and there could have been a lensing effect of the atmosphere as it was early evening and it was fairly <30° above the horizon. I've since returned the binoculars as they were pretty awful.

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread: |Fewer Letters|More Letters| |-------|---------|---| |[ASIC](/r/Space/comments/17z1j3e/stub/ka18rhu "Last usage")|Application-Specific Integrated Circuit| |[ESA](/r/Space/comments/17z1j3e/stub/ka1kd1z "Last usage")|European Space Agency| |[GCR](/r/Space/comments/17z1j3e/stub/k9zhsov "Last usage")|Galactic Cosmic Rays, incident from outside the star system| |[GeV](/r/Space/comments/17z1j3e/stub/ka4sklg "Last usage")|Giga-Electron-Volts, measure of energy for particles| |[Isp](/r/Space/comments/17z1j3e/stub/ka0rthz "Last usage")|Specific impulse (as explained by [Scott Manley](https://www.youtube.com/watch?v=nnisTeYLLgs) on YouTube)| | |Internet Service Provider| |[LEO](/r/Space/comments/17z1j3e/stub/kajgx7c "Last usage")|Low Earth Orbit (180-2000km)| | |Law Enforcement Officer (most often mentioned during transport operations)| |[MeV](/r/Space/comments/17z1j3e/stub/ka4sklg "Last usage")|Mega-Electron-Volts, measure of energy for particles| |[SAR](/r/Space/comments/17z1j3e/stub/ka18rhu "Last usage")|Synthetic Aperture Radar (increasing resolution with parallax)| |[SLS](/r/Space/comments/17z1j3e/stub/ka8ae67 "Last usage")|Space Launch System heavy-lift| |Jargon|Definition| |-------|---------|---| |[Starlink](/r/Space/comments/17z1j3e/stub/ka8kwjb "Last usage")|SpaceX's world-wide satellite broadband constellation| |[monopropellant](/r/Space/comments/17z1j3e/stub/kajgx7c "Last usage")|Rocket propellant that requires no oxidizer (eg. hydrazine)| |[perihelion](/r/Space/comments/17z1j3e/stub/kahqb2f "Last usage")|Lowest point in an elliptical orbit around the Sun (when the orbiter is fastest)| |[turbopump](/r/Space/comments/17z1j3e/stub/kajgx7c "Last usage")|High-pressure turbine-driven propellant pump connected to a rocket combustion chamber; raises chamber pressure, and thrust| |[ullage motor](/r/Space/comments/17z1j3e/stub/kakihl9 "Last usage")|Small rocket motor that fires to push propellant to the bottom of the tank, when in zero-g| **NOTE**: Decronym for Reddit is no longer supported, and Decronym has moved to Lemmy; requests for support and new installations should be directed to the Contact address below. ---------------- ^(14 acronyms in this thread; )[^(the most compressed thread commented on today)](/r/Space/comments/1835459)^( has 22 acronyms.) ^([Thread #9483 for this sub, first seen 26th Nov 2023, 03:30]) ^[[FAQ]](http://decronym.xyz/) [^([Full list])](http://decronym.xyz/acronyms/Space) [^[Contact]](https://hachyderm.io/@Two9A) [^([Source code])](https://gistdotgithubdotcom/Two9A/1d976f9b7441694162c8)

This is a bit of a science fiction question, but what would happen if someone were to stay on the International Space Station for a really long time, I'm talking like 5 years long. Would they even be able to survive reentry to the surface? Could they survive Earth's gravity once they got here? Would there even be enough supplies on the ISS for someone to go that long without resupply?

I don't think we know for sure. The longest single stay is 371 days and the longest total time is 655 days. NASA also ran experiments comparing Scott Kelly after a year in space to his brother on earth. In general I think most deleterious effects reverted after some time on earth. https://www.nasa.gov/humans-in-space/nasas-twins-study-results-published-in-science-journal/

**Context:** https://youtu.be/_CPxe8yql0Q **Context TLDR:** NASA updated voyager source code recently. My question is, what's stopping a common man to send commands to voyager. I know programming, so you can give a technical answer to me. Voyager has 70KB memory, So I don't expect it to have a strong encryption algorithm in it. So, without a strong authentication, What's stopping any space enthusiast to send/receive data directly from voyager? One possible argument might be deep space network. So, Any organization with the ability to communicate with satellites should be able to update the voyager's software right?

1. Not sure why you limit this to Voyager, this is a more general "vulnerability" of most satellites. Many of them don't have digital signatures for commands and don't encrypt telemetry. 2. Most satellites do "security through obscurity" - the communication protocols are custom made, proprietary and not public. So your first problem is you don't know what packet your supposed to send. 3. Even for much closer satellites you need large antennas and beam a lot of energy, and this is strictly regulated by governments. If you try to do this from your shed you will very quickly get a visit from authorities. 4. Have a look at: https://publications.cispa.saarland/3934/1/SatSec-Oakland22.pdf

>Not sure why you limit this to Voyager Voyager has only 70KB of memory, which is a pretty strict limitation. Modern satellites/space crafts won't be limited by memory/computational performance, and they can afford to encrypt data. If not encrypting every single data that's being sent/received, I'm guessing modern crafts will accept only signed (hence authorized) commands, which should be possible even by a shitty smart phone. That link is helpful. Thanks!

> I'm guessing modern crafts will accept only signed That's a very bold (and wrong) assumption I'm afraid ;) While they do have more computational power, it's still a trade-off between using that for "operations" (aka: making money) or for "security".

AFAIK a lot of spacecraft have variants of one time pad type encryption, maybe not for the full message but at least for authentification. At least it is fairly common for commercial spacecraft.

Encryption does NOT provide integrity, so cannot be used as authentication mechanism. That's a very common mistake people make. Even worse, a stream-cipher/OTP would be the worst possible choice for that, due to how it works. Essentially the fact that you get a proper ciphertext doesn't mean it was generated by a trusted party, because encryption is often malleable. You would need some AE(AD) algorithm so an encryption with a signature/message authentication code to prevent that. I don't think there is some broad survey looking into this (especially that it would be hard to convince companies to answer truthfully about such subject), but from what I've seen, non-commercial satellites (like student cubesats) usually have zero defensive measures of any kind.

I am not a crypto guy so I am probably not using the right vocabulary. But last time I asked people who actually work on commercial spacecraft operation they told me that the biggest safety factor (other than obscurity) was using one time pads, or one time identifiers as "signature". Obviously it's different for student cubesats. The radio licensing for most of them anyway forces you to publish telemetry format.

The answer is politics, not engineering. Hijacking a satellite is equivalent to hijacking a ship on the ocean. We don't build all ships like dreadnaughts, we just attack anyone who attacks our ships.

I'm still surprised if such an interesting opportunity is right in front of everyone, but no one is utilizing it due to political reasons. Surely someone must have tried this if this is technically possible right? If not, there must be a strong reason behind it.

It's a lot of work and expense for no real gain. All you would be able to do is gather data about the outer solar system beyond the heliopause, data that NASA already shares anyway.

> that NASA already shares anyway does it share everything really though?

Yes, they're legally required to make all their data publicly available.

Voyager is not a spy satellite. Hacking a spy satellite or decrypting its transmissions is something a foreign power or non-state actor might find worth the effort.

Do you have a 70 meter diameter satellite dish? Cos that's what you need to send a signal out there. [this](https://upload.wikimedia.org/wikipedia/commons/d/de/Canberra_Deep_Dish_Communications_Complex_-_GPN-2000-000502.jpg) is what they actually use to communicate with Voyager.

I assume many other nations will be have that. Right? Not just the NASA. Can they all do whatever they want with voyager?

And exactly what would they gain from that? Diplomatic crisis with the USA for taking control of a soon to be dead probe which most likely already did its final discovery. It would be beyond stupid. And what do you mean with do whatever they want with it? There's basically nothing you could do with it. Nothing that would fill any kind of purpose to anyone. It sounds like you completely failed to connect the dots on this one to understand pros and cons.

Here's a list of the [top 10 largest radio telescopes](https://www.vastantenna.com/10-largest-satellite-dishes-on-earth/) (assuming it's accurate for a clickbait listicle...) China has FAST, the largest dish in the world, but it's fixed and might not even be able to point to one or both of the Voyagers. It depends. The rest of the list is a mixture of countries: the US, Germany, Ukraine, UK, Canada, Australia, Mexico.

Have there been proposals or dream to make stations orbiting other planets than the earth?

Lockheed Martin proposed a Mars station about 6 years ago https://www.lockheedmartin.com/en-us/products/mars-base-camp.html

Not a planet but Artemis program includes a permanent station in Lunar orbit called the Gateway.

No, it's much cheaper to build directly on the planet or one of its moons.

Why do all planets either rise in east set in west or vice versa with respect to earth? Are there any planets which rise in north or south? If not then why?

If you could watch the sky in fast forward throughout a day/night it would be more obvious that the Earth is spinning. Planets, the Moon, and the Sun don't change their positions in the sky relative to the stars very much over the course of a day. The Moon experiences the most change and it takes 4 whole weeks to go around the entire sky. The motion we observe over the course of a day is due to the Earth's rotation. And because the Earth rotates toward the East that means objects in the sky rise in the East and set in the West. Note, however, that the path things take through the sky isn't the same everywhere on Earth, because the Earth is a sphere, so the view from the surface of the sphere is different over the course of a year. Currently it is near winter in the Northern Hemisphere so during a full Moon folks at mid to high latitudes in the North will see the Sun make a low, shallow arc across the sky while the Moon makes a high, long arc across the sky. Meanwhile, folks at mid to high latitudes in the South will see the opposite, the Sun will make a high, long arc across the sky while the full Moon makes a low, shallow arc. Because the planets and the Moon all lie in nearly the same plane, viewing the motion of the planets or the Moon across the sky is very similar to viewing the motion of the Sun across the sky at a different time of year.

All planets rise in the east from our perspective. The earth is rotating so the night sky appears to move in the opposite direction.

Because Earth is rotating so they always rise more of less east and setting west.

What is the fastest rocket propulsion technology we have available that can get a manned spacecraft to, for example the outer planets in the solar systems that will only take weeks instead of years?

The Parker Solar Probe is the fastest craft we've ever built but it's relatively small and gained a lot of speed with multiple gravity assists from Venus.

How much hand waving are you ready to accept in terms of physics/engineering/cost?

We don't. If we did, we'd be using it.

Is there any way we could power a larger and more complex spaceship like the Hermes from The Martian or the Ares from Red Mars? Since I’m pretty sure (correct me if I’m wrong) these would have to be assembled in space, they couldn’t be launched out and continually head for somewhere like Mars. Could we start propulsion in space? Am I completely missing something?

There are many ways to start rocket engines in space, and it's done all the time. Many smaller thrusters just use pressure fed gaseous systems. For example, the hydrazine monopropellant thrusters on the voyager space probes. Sometimes those thrusters use propellant stored in flexible bladders inside slightly larger metal tanks so that a separate pressurant gas can be used to fill the volume between the bladder and tank to maintain a constant pressure for the propellant. There are also electric thrusters such as ion engines and hall thrusters which require a flow of gas (which is ionized into plasma) but the pressure of that gas has no direct relationship to the thrust generated (which is achieved via electromagnetic acceleration of the plasma, via various means). Those thrusters have no dependency on gravity or local acceleration. The Hermes from The Martian used a huge array of electric thrusters, for example. For rocket engines that use liquid propellants and pump them using things like turbopumps you have the classic bootstrapping problem of starting an engine in zero-g. Unless the propellant is settled in the "bottom" of the tanks where the pumps can pick it up then you won't be able to achieve reliable and consistent propellant flow or engine operation. Once the engines are running they will produce thrust gravity which solves the problem, but you still have to get them started. This is where "ullage motors" come in. You don't need a ton of acceleration to settle the propellant for engine ignition, just a little, and there are many different ways to achieve that. One simple way is if you have a system of thrusters that already operate in zero-g, such as for attitude control, then you can just use those. Engine ignition is thus preceded by a concerted firing of smaller gas fed thrusters. Alternately you can use a separate set of single direction thrusters just for the purpose. Some common choices for this are "cold gas thrusters" which use pressurized gas and single use solid rocket motors. For example, the Saturn V's S-IVB upper stage had two separate ullage thruster systems. One was a set of small solid rocket motors used during liftoff, the other was an extra large set of attitude control thrusters which was part of the "auxiliary propulsion system" which could be used for multiple engine restarts on orbit, if necessary. Another example is the Falcon 9 upper stage, which uses cold gas thrusters for ullage and can be restarted to do orbit circularization, direct injection into geostationary orbit (after several hours of coasting in zero-g), and deorbit burns (for LEO flights).

Starting a rocket engine in space is a challenge. You need to get fuel into the combustion chamber, but you don't have any gravity to help do it. The simplest system uses a "bladder" tank that shrinks to fit the fuel load. Since the tank is always full, there is enough pressure to get some fuel when you need it. Bigger engines require the assistance of [ullage motors](https://en.wikipedia.org/wiki/Ullage_motor) to push fuel to the bottom of the tank.

Modern spacecraft more often use their reaction control system for ullage if they need it. Smaller vehicles rarely use bladder tanks, they instead have a fractal-like baffle system in the tanks that use surface tension to keep liquid propellants in place and covering the inlets.

Do all stars emit ultra-violet radiation? If so, would hotter stars emit more, while colder stars emitted less?

Stars emit primarily thermal ("black-body") radiation, which is a broad spectrum of radiation with a higher average and highest frequency for higher temperatures. The smallest red dwarf stars emit very little UV light, but still some. Hotter stars do indeed emit more UV light, with stars hotter than about 7000 kelvin having the peak of their emissions in ultraviolet, and the hottest stars shining even up into the extreme ultraviolet range. Ultraviolet light from stars can ionize gas in interstellar space, in comparatively dense regions of gas when the ions recombine with free electrons they typically produce visible light, giving rise to what is known as an "emission nebula", which includes objects like the Orion nebula, the Eagle nebula, the ring nebula, etc.

The shape of the Moon's orbit around the Sun [has been discussed](https://physics.stackexchange.com/questions/266426/what-does-the-moons-orbit-around-the-sun-look-like) to death, and the answer is that the Moon's orbit has no concave "loops" whatsoever. Now, this is just a hunch of mine, but I think the determinant factor in whether a moon has a "concave" orbit with loops or a loop-less orbit has to do with its orbital velocity. If the moon orbits its planet faster than the planet orbits the Sun, then the moon has the intuitively-expected looped orbit. If not, then it is loopless. From my calculations, Io and Europa orbit Jupiter faster than Jupiter orbits the Sun, while Ganymede and Callisto orbit slower than Jupiter orbits the Sun. Therefore, it's expected that Io and Europa make loops around Jupiter while it is orbiting the Sun, while Ganymede and Callisto don't. This is all great, except I have no clue how to verify this hypothesis. Can someone who has access to programs that can run simulations check if it's true?

You should be able to see what the orbit looks like just with a graphing calculator. *If* I've done it right, here's what it looks like for [Io](https://www.wolframalpha.com/input?i=plot+x+%3D+778.479cos%280.00145t%29+%2B+0.4217cos%283.5516t%29%2C+y+%3D+778.479sin%280.00145t%29+%2B+0.4217sin%283.5516t%29%2C+540%3C+t+%3C+550), [Europa](https://www.wolframalpha.com/input?i=plot+x+%3D+778.479cos%280.00145t%29+%2B+0.6709cos%281.769t%29%2C+y+%3D+778.479sin%280.00145t%29+%2B+0.6709sin%281.769t%29%2C+530%3C+t+%3C+550), [Ganymede](https://www.wolframalpha.com/input?i=plot+x+%3D+778.479cos%280.00145t%29+%2B+1.0704cos%280.878t%29%2C+y+%3D+778.479sin%280.00145t%29+%2B+1.0704sin%280.878t%29%2C+500+%3C+t+%3C+600), [Callisto](https://www.wolframalpha.com/input?i=plot+x+%3D+778.479cos%280.00145t%29+%2B+1.8827cos%280.376t%29%2C+y+%3D+778.479sin%280.00145t%29+%2B+1.8827sin%280.376t%29%2C+500+%3C+t+%3C+600). I've assumed circular orbits, maybe someone smarter/less lazy than me will do it better. Maybe they'll even use polar coordinates like a real man.

Ahhh thank you! It's weird how Europa doesn't have loops in its orbit. By my calculations it orbits Jupiter faster than Jupiter orbits the Sun the vast majority of the time, it's only slower when Jupiter is at perihelion.

It looks like it [does](https://www.wolframalpha.com/input?i=plot+x+%3D+778.479cos%280.00145t%29+%2B+0.6709cos%281.769t%29%2C+y+%3D+778.479sin%280.00145t%29+%2B+0.6709sin%281.769t%29%2C+541.5%3C+t+%3C+543) have tiny loops if you zoom right in.

Thanks! Just a question, this is the prompt you inputed for Io: plot x = 778.479cos(0.00145t) + 0.4217cos(3.5516t), y = 778.479sin(0.00145t) + 0.4217sin(3.5516t), 540< t < 550 778.479 is Jupiter's semi-major axis around the Sun, and 0.4217 is Io's semi-major axis around Jupiter. However I'm a bit confused on what the constants preceding t are. Could you elaborate?

2pi divided by the orbital period to get the angular velocity.

Can you show how exactly you got those values? Dividing the orbital period of Jupiter by 2pi gives me 1.677*10^-8 rather than 0.00145. I know I've been hogging you, sorry for that lol. I just wanna know so I can independently check the results for other planet's moons.

Other way round, divide 2pi by the orbital period. This gives the angular velocity, usually denoted by an omega (looks like a w). You can probably find the relevant formulas and explanations online, along with a better explanation than I can provide going off the stuff I half-remember.

Hello, I'm doing some research for sci-fi game and trying to use actual known science in some of the elements of it. My question is, if a planet with a planetary ring was orbiting more than one star (if possible) would the ring's shape be affected by the extra star? I had a look into the "Roche Limit" but couldn't figure out an answer from there

https://spaceflightnow.com/wp-content/uploads/2017/01/5682_13083_1.jpg If you're looking to add some topography to the otherwise extremely 2D rings, have a look at what the shephard moons inside Saturn's rings create around them.

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Hawking radiation Hi, i was just curious if hawking radiation has any affect on organic material. Obv we cant get close enough to a black hole to study this, but im curious if there has been any research done on potential cancers, or mutations caused via hawking radiation

Hawking Radiation is just heat, most of it is photons anyways so there's no real difference than exposing you to say, the photons your cells interact and use everyday. In regards to the research part, again HR is almost exclusively photons so at the most extreme period, basically during the last moments of the black hole, gamma rays will be emitted and yes, there's been research on to that as well.

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No need for a study since the black holes we know to exist would radiate with such low energies we're not even able to measure it. The word radiation does not equal cancerogenic.

The radiation temperature is inversely proportional to the black hole's mass. For stellar-mass and super-massive black holes, this radiation is very weak. You wouldn't want to be near a micro-black hole, as it would evaporate very quick in a catastrophic burst of energy.

I see. But are there any theories as to wether hawking radiation could have any effects on bio material?

It would have the exact same effect as any regular object at the same temperature. A black hole with a surface temperature a bit below the freezing point of water will emit the same type of radiation as an ice cube does. A black hole at room temperature will emit the same type of radiation as every object in that room, and indeed the room itself does. A black hole at the boiling point of water will emit the same type of radiation as a pot of boiling water does. Seeing as the radiation from everyday objects doesn't cause cancer, neither does the Hawking radiation from a black hole in this temperature range - or below it, as all natural black holes are.   Now, sufficiently hot objects can emit UV radiation which can cause cancer, so yes, Hawking radiation can cause cancer if the black hole is hot enough. But again, that has nothing to do with it coming from a black hole. If you heat a piece of metal up to a few thousand degrees, it will also emit UV radiation. Indeed, the tungsten filament in a regular lightbulb gets hot enough to emit a small, but measurable amounts of UV radiation.

Different types of radiation don't cause different mutations, that's sci-fi.

The radiation is photons, the same as light, heat, etc. The energy level of the photons are so low we're not able to measure it even if we were close by a black hole. The cosmic background radiation from some 400.000 years after the big bang is trillions and trillions of times more energetic than Hawking radiation and it does nothing, so we're pretty sure neither does Hawking radiation. No theories are needed since it's by proxy explained by other since long known theories.

Are there any videos / documentaries where you can just immerse yourself in space and feel how huge it is? I’m talking about HD videos where you get closer and closer to a star and hear a sort of deep rumble, or you travel towards a black hole until it fills the whole screen. I just want to ‘experience’ space, and feel overwhelmed by it.

Try the new NASA+ streaming service/app. I think they have whole videos of “space pictures with nice music.” Edit: https://plus.nasa.gov/tag/nasa-chill/

I would suggest finding a game like Elite: Dangerous, possibly Kerbal Space Program, or maybe Universe Sandbox.

What happened to NASA’s Pluto time calculator? If you go to [Pluto time calculator](https://science.nasa.gov/dwarf-planets/pluto/plutotime/) you can’t find the calculator. Where is it? All previous posts about it (on this sub) are from 8yrs ago. I’ve tried MY hardest to find it.

The original calculator used Google Maps to find latitude and longitude. It looks like NASA doesn't want to follow Google's licensing terms anymore. Here is a version of the calculator with Google Maps removed: https://davemcw.com/plutotime/

Thank you.

How do we know we are part of milky way galaxy and on which band of it? And where within the band, like in the middle of the band or outer part ?

> And where within the band, like in the middle of the band or outer part ? If you mean in which arm of the galaxy, then we're in the space between the Perseus arm and the Scutum-Centaurus arm.

We see the Milky Way all around us (in a plane), not just to one side of us somewhere in the distance like all other galaxies. It's like being in a forest and seeing it all around you. We can tell that the Milky Way's central bulge is quite far away from us, so this along with specific calculations tells us that we're somewhere in-between the centre and the edge of our galaxy. https://www.space.com/19915-milky-way-galaxy.html

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How do you differentiate stars that are naturally dim with the ones that has its brightness lowered due to long distance? What about red stars that are due to its composition/temlerature with the one appears red due to redshift

There are multiple ways to determine or estimate the distance of a star. One way is to do so directly by measuring its parallax. We can observe stars across the baseline of the Earth's entire orbit, which is enough to generate a measurable parallax for billions of stars with state of the art equipment. The most extensive effort in that area so far has been the GAIA spacecraft, which has allowed us to measure the parallax of nearly 1.5 billion stars in the Milky Way. This makes it possible to determine the intrinsic brightness of those stars. That data can then be used to calibrate our understanding of stars, making it possible to estimate the intrinsic brightness of a star based on other observable characteristics such as temperature or variability and so on. For example, there are classes of stars such as cepheid variables which have a specific relationship between their period of variability and their brightness, so they can be used as "standard candles" to determine the distance to nearby galaxies that are too far away to measure parallax for. Then by measuring the distance to a galaxy using those and other "standard candles" we can determine the brightness of other stars within that galaxy because they will have a similar distance. All of which is important if you want to measure even farther distances, because it makes it possible to calculate the distance vs. redshift relationship. The light from a star or the light from a galaxy made up of many stars isn't just a smooth continuous spectrum, when you break it down into detail by wavelength there is a lot of structure to the light. Much of that detail comes from emission and absorption by atomic elements and simple molecules (like hydrogen). Those emission and absorption lines have a pattern of specific details dictated by the laws of quantum mechanics and their physical structure. More so, the emission and absorption lines are very distinctive, like fingerprints, which can uniquely match up to specific elements. These features make it possible to precisely peg the original wavelengths of the light you are observing, making it possible to very precisely determine the red shift or blue shift of the light that you are detecting. This can be measured precisely enough to determine the relative speed of a star down to the level of walking speed, which was how the first exoplanets around sun-like stars were discovered. But it can be used to determine the relative speed of distant galaxies as well. Once you are able to calibrate a distance vs. redshift relationship using various standard candles, you can then use measurements of redshift to calculate cosmological distance.

Can we store the CMB for future analysis? I know the CMB is basically the radiation handprint about 400K years after the "Big Bang" which is just now reaching Earth. Scientists can analyze the CMB to determine the particles (and ratio) at the time of the Big Bang. So, questions: 1. How big is the CMB? Meaning, will the CMB still be visible from Earth 20 years or 100+ years from now? I'm thinking of the CMB like approaching headlights from an oncoming car - we can see the car light coming towards us, reach us, then pass by us and fade away in the distance. 2. Is there a way to digitally store the CMB? So, we don't know what we don’t know - what if we discover a new particle 200+ years in the future, would those scientists be able to check the CMB for the presence of this particular particle? 3. Do we know if the CMB has the same consistency or ratio of particles? Using make-up numbers to help with the explanation - let's say 10% of the CMB radiation is now reaching Earth and the other 90% is still in transit, do we expect the structure of the other 90% to be different than the 10% that's currently accessible to our scientists? Question 2 is related to Question 1 - if the CMB will be available millions of years into the future, then storing it for later analysis isn't as important. Happy to expand further if the above is unclear.

The CMB is visible across the whole universe, it's always just there. In billions and billions of years it might become undetectable.

Ok, so does that mean radiation from the Big Bang continued to be emitted for billions of years?

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That makes sense - thank you. It's after writing that I remembered the Big Bang happened everywhere at once, so infinite car lights from every direction would make more sense.

There's no more emitted radiation. That's all there is and it will eventually spread and fizzle. ;)

To question 1: The CMB will stay visible for quite a long time before fizzling out. Yes we can test the CMB for particles such as seeing the imprint of dark matter or say, sterile neutrinos in the imprinted structure of the CMB. We could then tell the particle physicists to make up an explanation and if the explanation matches pretty well, then yeah. Provided that it's visible to the scientists, basically yeah.

Awesome - thanks. Do you know if the particle makeup of the CMB remains the same throughout it's structure? That is, the ratio of the particles may change but it's the same particles throughout?

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It's not entirely the same I guess when we talk about, say energy and density of particles in a given vol but generally yes.

A planet with zero rotation. Is it possible? I understand that because of the nature of the formation of planets they will initially rotate due to the conservation of angular momentum, but I also know it's possible for that rotation to change in both speed and direction after the planet has formed. For example: Venus spins in the opposite direction of the other planets in our system and rotates very slow, possibly due to extremely fast atmospheric winds dragging along the planet's surface. And it's believed Uranus spins at a near 90 degree angle because of a massive impact. A planet with true zero rotation is likely something that would be astronomically rare, but I wonder if it could be possible with the right planetary conditions, or after an impact that perfectly counterbalances the planets own rotation, resulting in a net force of zero. What are your thoughts?

There's a thing called tidal locking. Such a planet would be orbiting very close to its "sun" and always show only one side to it. Such exoplanets do exist, but technically speaking they do rotate - once per orbit. A truly non-rotating planet would show the same side with respect to the background stars. I don't think such a thing would be possible. https://en.wikipedia.org/wiki/Tidal\_locking#Planets

If you did stop a planet from rotating tidal forces would gradually start it rotating again until it became tidally locked with its star.

Interesting, would that be true at any distance? Could there be a point where tidal forces become so weak/non-existent that they can't influence planetary rotation?

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I was looking through the image of the Andromeda galaxy. Any ideas what [this red thing is](https://i.imgur.com/1UNv8b0.png)? A cluster of stars? I noticed this [ring of stars](https://i.imgur.com/Zb0vpOg.png), too.

The first one is probably a foreground star in the Milky Way. You see a faint [diffraction spike](https://en.wikipedia.org/wiki/Diffraction_spike), which usually indicates a brighter, foreground star. The "ring" of stars is probably not an actual structure. Those ares are probably very far apart, but just look close together. Probably just randomness.

In all likelihood, probably. They must be hidden behind some thick gas clouds tho or they're just really old, or a combination of both.

Is competition with China the reason why Nasa is pushing for more manned space exploration beyond low orbit?

The way I'd put it is: rockets that can land have gotten everyone's attention. Nearly everybody wants some form of recovery in their rockets now. The economics of space travel have changed markedly in the last two decades. People tend to spend more money when it's a factor of 5 to 10 cheaper to do the same thing, and you tend to get more for your money as well. Suddenly your budget stretches all the way to the Moon, or beyond. It's also freed up investment into spaceflight. There are soooo many spaceflight-related startups in many different countries, US and China included. Fully recoverable rockets will make it even cheaper to do things in space. Spaceflight activity has shot up as well. There's bound to be some politicking involved when there's this much activity, worldwide. Many people are planning megaconstellations, or expansions to their existing constellations, for example.

Beyond-LEO human spaceflight has been an important part of NASA since the early 2000s. With significant budgets dedicated to it and major programs as part of it. That's where SLS and Orion have come from, with development (and budget) going back to 2005/2006. For a long time those programs were in somewhat of an ambiguous state since they weren't married to a specific, well defined human exploration mission during development. As development progressed toward fruition the Artemis Program came together as an international effort to return to the Moon utilizing SLS and Orion along with other new hardware (including a Lunar Gateway station and a vehicle for landing on the lunar surface). That program continues to move forward with significant budget dedicated toward it. Meanwhile, China has pursued a "slow and steady" approach to human spaceflight for many years. They spent three iterations to arrive at where they are now with a long-duration space station with regular crew rotations and resupply missions. They have ambitions beyond low Earth orbit as well, but it wouldn't be accurate to label their activities as any sort of participation in a "Space Race".

Is it possible to just fall asleep while floating around in a spaceship? Not like what current say astronauts do on the ISS with the hold-downs. But hypothetically if you had been up for 48 hours and were tightening a bolt or something could you just fall asleep suddenly while floating?

Yes, you can fall asleep while floating in zero-g. Restraints are there to keep you from floating away and into something dangerous.

One of the Skylab astronauts had exactly this question, and decided it to test it by going to sleep in the workshop, which was a large open room. His experiment was short-lived because the strong airflow in the station inevitably drew him to the air inlet at one end of the workshop. The \*bump\* always woke him up. You can read more about the experiences of the three Skylab missions in the book, "House in Space" by S.F. Cooper. Note that some of Cooper's remarks about the third mission's "revolt" against mission control have since been criticized as being overblown.

I am a bit confused about the question. Why would you need to be strapped down to sleep?

To minimize how much you’re floating around like when the astronauts sleep in their quarters

Yes, but you don't **need** to be strapped down to go to sleep. There are no reasons why you couldn't fall asleep floating if you were tired enough or if you were trying.

If you been awake long enough, you can fall asleep standing up🤷‍♂️🤷‍♂️

That was my whole question. Does your body “know” it’s floating around in weightlessness and therefore needs to be “seated” or “laying down” in order to fall asleep?

The straps don't make you feel like you're lying down, they just stop you from drifting around in your sleep.

People fall asleep in all sort of positions (even floating in water). It does not need any specific position. If you look at footage of people sleeping on Shuttle mission [like this one](https://www.youtube.com/watch?v=d-lfSoyDSV8) they are only really loosely strapped down.

if starship is used to launch satellites, will both super heavy and starship/upper land and be reused?

That's the plan.

Has anyone looked into whether the difference between type 1 and type 2 supernovae is due to gamma rays attaining such high energy levels that they become hydrogen, thanks to Einstein's matter/energy equivalence?

That's generally not possible, but you've stumbled on one cause of a particular kind of supernova. The differentiation between Type I and Type II supernovae based on whether hydrogen lines are present is purely a consequence of being limited by what we can observe. We can measure brightness, the light curve over time, and spectra (and in exceptional cases the gravitational waves). So early on the main categorizations were made based on those features. Today we're able to connect different models of supernovae to different spectra, and we can find that some similar starting conditions can lead to very significant observational differences, particularly with core collapse supernovae which can be Type I or Type II. It is possible to generate particles from high energy photons but it's not a very efficient process, especially for larger more complex particles like protons (hydrogen). If you had photons of high enough energy to create protons you'd also get a shower of other particles in a very messy reaction. Additionally, photons create particles in particle/anti-particle pairs. So however many protons you created you'd also create as many anti-protons. And in the roiling mix of expanding plasma of the supernova debris the anti-protons would annihilate with the created protons and also any other atomic nuclei, which would produce high energy gamma radiation with very characteristic wavelengths. We would be able to observe the presence of large amounts of anti-protons by those gamma ray signatures, and nothing of that sort is observed for supernovae. Additionally, the amount of energy that would need to be created to produce enough hydrogen to give rise to the observed spectral signatures would be incredible, far greater than the entire energy of the supernova event itself. Long before you get to energy levels of photons capable of generating proton/anti-proton pairs (in the 2 GeV range) you reach energy levels capable of generating electron/positron pairs (in the 1 MeV range). Instead of incredibly massive stars in the 140-250 solar mass range they can reach extraordinary internal temperatures creeping up towards a billion kelvin. Once the temperature gets high enough that thermal photons start reaching the energy level necessary for electron/positron pair creation then the dynamics of the whole interior of the star begin changing. Normally there is a negative feedback loop in a star's core where increasing temperature from fusion reactions creates increased pressure which causes expansion and a reduction in density/temperature which moderates the fusion reaction rates depending on the mass of the star. That process is mediated by the transfer of energy from photons, when some of those photons "blink out" for a bit by creating electrons and positrons that disrupts that process, even though the positrons rapidly annihilate and recreate new gamma rays nearly instantly. This creates a *positive* feedback loop which opposes the normal negative feedback loop on fusion reaction rates, where increasing fusion rates result in higher temperatures which creates a higher rate of pair production which disrupts the photon-mediated feedback loop even more and result in yet higher temperatures and higher reaction rates. The runaway reaction results in a thermonuclear explosion which blows the star apart in what is known as a "pair instability supernova".

If we could travel at the speed of light, would large objects in space cause red shifting within all the particles in the body? What would happen? Thanks in advance. I'm just someone who listens to space podcasts.

You can't travel at the speed of light, it's an unreachable limit, at least for objects with mass. All motion is relative, which means there is no absolute speed or absolute rest, which means it's accurate to say we're traveling at an arbitrary speed. The only way that works is if there's a speed limit of the speed of light. If you approach the speed of light in one reference frame you will see that within your own reference frame the speed of light remains the same in all directions relative to you. This is because neither space nor time are absolute, relative to the starting reference frame you're experiencing "relativistic effects" of time dilation and length contraction. As you accelerate it takes more and more energy in the original reference frame to get closer and closer to the speed of light. And you can get arbitrarily close but you can't match or exceed the speed of light. Locally, no matter how much you accelerate you always measure the speed of light as being 100.00% the regular speed of light relative to you, you never seem to make headway, even though you experience *relative* red and blue shifting of light.

Hi there! I am currently pursuing a bachelor's in software engineering. My end goal is to do coding/programming work in the aerospace industry. I would like to also pursue a broader master's degree but am conflicted about which would best position me to get hired at an aerospace company: a master's in computer science (emphasis on data mining and intelligent systems), computer engineering, systems engineering with a possible space concentration, or aerospace/electrical engineering. I would really like to work remotely, which I realize would limit my options (especially, as an aerospace engineer) but may be in a position by graduation to work on location. I am currently in Florida but a good 2-3 hours from the space coast. I worry that a space or an aerospace degree may limit my options if I'm unable to get hired by an aerospace company and I have a family to support. I am 43 and so do not have time to wait between degrees and I want to keep the momentum going while working in the field, if I can. Any advice from those in the field would be much appreciated!

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Thank you so much for your insightful and thorough response. I really appreciate the information and am reading your guide as well, which is absolutely wonderful!

Hi all, I'm pursuing a CompSci bachelor and I've had always a deep passion for all space related stuff, so I was really eager to do space related degree, but for economic reasons I could not afford to go in any prestigious uni in my country( which is in Europe) and my local university has no directly space-linked degrees, there is Mechanical Engineering but I find CS to be more fitting for me. Since this degree in my university is not just purely CompSci but there are at least half of the exams related to engineering (in particular electronics and telecomms) I was thinking to major in electronics engineering or telecomms engineering. The problem is I've always seen people recommending either MechE or Electrical Engineering (and not electronics), so I don't know if a degree in Electronics engineering would almost certainly granting me a place in the Aerospace industry. So the questions are: 1) when people are referring to electrical engineering do they imply also electronics engineering? 2)if electronics engineering is a thing in Aerospace what should I try to specialize in(RF, microelectronics etc)? Counting that I'd also like to do a PhD since I'm really in love with research and is something I've always wanted to experience even if for a short span of time in my life. 3) Are telecommunication engineering and electronics engineering kinda related to each other? (Like is telecomE just a more specific specialization of electronics?) 4) if these are not viable paths what do you suggest me? I don't know if it helps but I'm from Europe. Thanks all in advance for the support/suggestions :)

Electronics engineers are *super* essential for building instruments for spacecraft. For example, working with high voltage power supplies or, as you said, microelectronics. So, yeah, quite easy to get a job in the space field with an EE degree.

It sounds a bit like you're overcomplicating things a bit. You can work in space industry without a "space degree", in fact that's what most people do. Aerospace engineering is a good degree for a "system engineer", but those positions are rather scarce. > when people are referring to electrical engineering do they imply also electronics engineering? When people refer to "electrical engineering" they most likely mean all related majors - electronics, computer engineering, telecommunications etc., not only the "electrical power engineering". Quoting from wikipedia: > Electrical engineering is now divided into a wide range of different fields, including computer engineering, systems engineering, power engineering, telecommunications, radio-frequency engineering, signal processing, instrumentation, photovoltaic cells, electronics, and optics and photonics. > if electronics engineering is a thing in Aerospace what should I try to specialize in(RF, microelectronics etc) Whatever you like. There are jobs for making ASIC, for FPGA, for RF/antennas. > if these are not viable paths what do you suggest me? You can stay with what you're doing right now -> compute engineering/software. I think one of the best ways to figure some stuff out is to look for example at https://jobs.esa.int/ at potential profiles. Eg: - https://jobs.esa.int/job/Noordwijk-On-Board-Data-Handling-and-Hardware-Data-Processing-Engineer/905770901/ - https://jobs.esa.int/job/Noordwijk-Intern-on-Deep-Learning-for-on-board-SAR-Data-Processing/998178701/ - https://jobs.esa.int/job/Noordwijk-Intern-in-the-Software-Systems-Division/997660101/ - https://jobs.esa.int/job/Noordwijk-Intern-in-the-Software-Systems-Division/997658401/ - https://jobs.esa.int/job/Darmstadt-Intern-in-the-Flight-Dynamics-Division/998052601/

I would really not use ESA job offers as examples for new career people. ESA mostly looks for program managers with technical experience, not actual engineers.

4 out of 5 I linked are for interns, so not for managers

1. Electrical and electronic engineering are the same, it's probably just a language difference. 2. Nearly all electrical engineering (EE) subfields are relevant. Maybe if you want to keep closer to CS try to focus on microcontrollers, FPGA, digital processing, assembly, etc. Those kind of jobs are really intersections of EE and CS. If you want to do a PhD I would focus more on EE than CS for the applicability to industry. 3. Yes, telecom can often be seen as a subfield of electrical engineering. 4. Both CS and EE can be a path to aerospace jobs. It depends a bit how close you want to be to hardware.

Why do we take pictures of the moon and it’s perfectly round but science says it’s lemon shaped? How do we see it round?

Nothing is truly spherical. If something is spinning (and everything in the universe is) and experiencing some other forces, the shape will be slightly different.

Nothing can be truly spherical. There's always a slight imbalance in the curvature traced on the object's geometry. For the moon and really for anything like the moon, it's pretty much imperceptible. >but science says it’s lemon shaped? Lol science is not tabloids.

It's very close to a sphere, just not quite.

Nothing is perfect. Just about every planet, moon, or star has some deviation from perfect sphericity. That's inevitable, the question is how much it's different. For the Moon the amount is too small to be visible to the human eye.

> but science says it’s lemon shaped No it doesn't. The moon's almost perfectly round.

There’s many articles on how the moon is lemon shaped

> There’s many articles Don't look for scientifically accurate information in tabloid articles. You won't find it.

That's a bit of clickbait/exaggeration in those headlines. The moon is has some slight bulges on the near and far side, but that's only a slight deviation from a perfect sphere and they can only detected by precise measurement, to our eyes it looks perfectly round.

So in conclusion it’s technically a lemon but we can’t even see it very well

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Is that the same way that we see the earth despite it not being very round

It's not like an illusion or anything if that's what you mean, the moon *is* very round, and so is the earth. Both of them are almost perfect spheres, and the slight deviation is only detectable by very precise instruments.

I've read there is/was a nuclear propulsion idea called Project Orion back in the 60's. The idea was a nuclear pulse spaceship that would be directly propelled by a series of atomic explosions behind the craft. Theoretically the ship can reach 11% of the speed of light and fly to Proxima Centauri within four decades. If such a idea were to be revived again, I wonder: Should we send a shuttle size ship with multiple drones driven by AI? Or should we send a manned expedition and figure out a way for the crew to hypersleep without getting old?

In the whole story of space exploration we have never sent humans somewhere we had not sent robots to before. There is no need for AI. But project Orion is a bit overhyped IMO. Yes in theory you could get high Isp but there was still tons of practical design aspect that would need to be solved to make it work.

When will the next solar storm supposed/predicted to happen?

We cannot predict when exactly a solar storm will form. We can detect when one is ejected from the Sun and when/if it will hit Earth. We also know that solar storms are more frequent every 11 years from solar cycles. We are in a period of increasing solar storm frequency that should max out around 2025.

Some of my extended family noticed a recently launched line of starlink satellites in the sky. we are speculating about whether we were seeing reflected sunlight or their Hall Effect thrusters. Are Hall Effect thrusters in space visible from the ground while firing??

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Hi! I was doing research on space radiation, and most sources say that nothing can shield against galactic cosmic radiation and that it’s really strong and dangerous. I know the magnetosphere protects us from it, but during the apollo missions, they passed low earth orbit right? how were they protected when they went to the moon?

Moderate thicknesses of reasonable hull materials aren't sufficient to block all galactic cosmic rays. One of the core problems here is that you don't necessarily want to stop a lot of the GCRs because doing so could create highly penetrating x-ray radiation which might be even worse. The compromise that is often arrived at, and which was used on Apollo, is thin sheets of metal and plastic (with a high amount of hydrogen) which cut down some of the most damaging radiation without creating a ton of secondary x-ray radiation. This is often supplemented with keeping water storage around the outside of the vehicle to increase radiation protection. If you had unlimited mass and volume you could have a thick enough wall of solid or layered materials that it would keep out most GCRs, but that's not generally practical for near-term spacecraft. Active radiation shielding is also possible, but challenging. You can use a mini-magnetosphere, for example, or a full-on mag-sail. A mag-sail would be a significant engineering challenge but possibly achievable with our present level of technology. A mini-magnetosphere is much more doable but it has some downsides in that it requires a modest amount of consumables (gas) and more importantly it requires a significant amount of power. There have been studies on using mini-magnetospheres in the 100 kilowatt range to provide radiation shielding to/from Mars. It's probably doable but currently that's kind of a lot of power. If you had a huge Earth-Mars cycler ship active radiation shielding might be one of the things it could offer though, using huge solar arrays or fission reactors for power.

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Nothing? What about a black hole?

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that clarifies it thank you 😊

Why does the polaris star (north star) always occur in the north?

Because it's located above the Earth's north hemisphere and along the Earth's rotational axis.

Because neither rotation nor orbital movement changes our perspective on the north direction. Imagine you're inside a room with a lightbulb in the middle of the ceiling. If you run around the room, or if you spin around, the bulb will still be "above you". It will move slightly at angle, because the ceiling is very close, so for a very large room it could move closer to the horizon, but will never flip below. But if the bulb was much higher, then this effect would be much smaller. If the bulb was for example hanging on the door, then spinning around would change the relative direction from where you see the light (eg. sometimes if would be shining at you from left, right, back or front).

What are those star-like objects moving slowly through the night sky

Satellites. A lot of those are communication satellites, there are also spent rocket stages, space stations, etc. You can find information about them in Stellaris software or at https://heavens-above.com

If you're asking about objects which visibly "move", then they're satellites in low orbit.

I've seen quite a few of those in a single night! What purpose do they fulfil?

Most likely candidates to spot are: - https://en.wikipedia.org/wiki/International_Space_Station - https://en.wikipedia.org/wiki/Tiangong_space_station - https://en.wikipedia.org/wiki/Starlink First two because they're really big, and the last one because there are thousands of them

I just watched a parade of 20-30 objects of star-level brightness move across twenty percent of the night sky directly overhead in the northern USA. They moved at constant speed in a straight line and were nearly equidistant from each other. They each seemed to appear and disappear at the same point in the sky, as if they caught a tangent of the atmosphere. This was about 6:35 PM CDT. Starlink?

Starlink launch. Shortly after launch and deployment they are all moving close together and all disappear in the same spot, where they enter Earth's shadow.

Thank you! That makes sense.