How “See a Satellite Tonight” Works | Hacker News Reader

How “See a Satellite Tonight” Works

james.darpinian.com

194 pointsmodeless27 comments

When I was in school two decades ago I wrote a program to scrape Iridium Flare passes from HeavensAbove, filter on time and magnitude, cross-check with cloud coverage from Weather Underground, and put good viewings in my calendar with a vibrate alarm a few minutes in advance (which synced to my Palm Pilot). It felt precognizant to walk out of a lecture and be like, "Hey look up at the sky right over there!" and we'd all see the flash.

I urge anyone interested in the topic to read T.S. Kelso's (maintainer of Celestrak) pieces on "Computers & Satellites" [1] and generally browse Celestrak - a true goldmine. J.C. McDowell [2] is also undertaking similarly impressive work.

Thanks for this great app OP. I will keep a sharper eye out in the next nights from now!

[1] https://celestrak.org/columns/ [2] https://planet4589.org/index.html

This website is incredible. It blew my mind when I realized it was showing a star map superimposed on a street view image of our actual location.

A question from a very inexperienced stargazer - we went outside to look at the Starlink constellation that was passing overhead, and in the five minutes we spent looking for it, we couldn't see anything moving on that trajectory but did make out three apparent satellites moving on different trajectories, satellites apparently not known to the web app. Is that plausible or is it more likely we were mistaking airplanes or imagining things?

Thanks! It's plausible that you might not see predicted satellites and very plausible that you would see extra ones. Predicting satellite visibility is very difficult because it depends on unknown factors like the shape and BDRF and precise orientation of each satellite. My site necessarily uses a simplified model, which will sometimes be wrong in both directions. There will be many visible satellites in the sky that aren't shown on the site, and some that are shown on the site may end up not being visible after all.

For a guarantee of visibility look for satellites marked "bright" in the UI (which will usually be ISS or Tiangong). For a more comprehensive catalog of satellites that may or may not be visible, check out sites like https://www.heavens-above.com/.

In a period last (or previous?) winter I chased sattelites based on this great page and concerning starlinks I only had luck with using a monocular (or binocular of course). Perhaps partly because my eyesight is not that sharp as it was in childhood and also this area is moderately light polluted. I only have a 8x magnification monocular (lower would be better) which made the chase of the moving stream of satellites difficult but equally exciting and spectacular. It is a bit of luck catching the satellites through the lens (in which the page helps tremendously showing where to look in real time), the magnification amplifies the speed in front of the stars and consequently the observation turns into a high speed chase. Occasionally I seen slow moving, lone, bright ones with the naked eye but those were boring compared to the high speed chasing of a stream of elusive dots. : )

Not sure if the author will see this, but it's a story I want to share.

Early in the lockdowns, I was using this website to be able to connect to some friends and family who live 300km away in a different country. Due to travel restrictions it was hard or impossible to travel to see them. And I am not very much a talking person, I kind of need to do things to connect with people.

I would tell them when they could watch the launch of the SpaceX rockets. Then I would use this website to check when the satellites would be passing. At the time, it was easy as SpaceX was launching a lot of very reflective low orbit satellites for Starlink. When the opportunity arose, I would call my family again and send them this amazing website. While calling on the phone, we could then connect while we were both trying to spot the same satellite.

Once we could both see those satellites at the same time, the world felt a lot smaller and the distance did not feel so bad.

For me, this website made a big difference.

Thanks, I'm glad to hear it!

"I imagined that people would come across my site, even people who had no prior interest in satellites or the night sky at all, and it would immediately tell them that ISS is coming over in five minutes, and they'd go out and see it and be amazed at the sheer craziness of knowing that there are people up there. They'd grab their child or their parent and show them too, and it would spark an interest in science and space in a few more people in the world."

That's me! I even address people who happen to walk by when I've spotted a sat. They love it!

It is indeed the ISS that gets most enthusiastic reactions. Parents with their kids love it.

I like to imagine one of these kids will "get it" and will forever inspired :)

James, thank you for the site. It has brought many smiles to my face.

My initial thought was "wow, this would have been cool when I was a kid, but now I just need to look up!"

And then I actually went to the site. Holy crap. It's really incredibly well done. Kudos!

It is great if you live somewhere with low light pollution. Stare at the sky long enough then you notice steady moving lights.

I did a couple of astrophoto sessions (noob) but that was a great experience just staring up.

It also works surprisingly well for people in cities, such as myself when I'm at home in London.

Fortuitously, I'm so glad to have checked this just now as apparently there's going to be a Starlink train going over where I am at the moment on holiday, in a couple of hours - bonus! :)

Yes, it is equally cool over 50!

I'm seeing two fly-overs of the ISS like an hour and a half apart. Can that be correct?

Seems about right. According to https://www.nasa.gov/feature/facts-and-figures

> In 24 hours, the space station makes 16 orbits of Earth, traveling through 16 sunrises and sunsets.

Is it possible to see Starlink satellites with your eyes?

Yes. (I have.)

They are launched into low orbits where they are often visible to the naked eye, as a train of 50 or more satellites following each other across the sky. It's quite a sight.

Over a few weeks they raise their orbits to operational altitude. Once they reach it and orient themselves for operation they are much dimmer and can't be seen without magnification. So the vast majority of orbiting Starlink satellites are invisible to the naked eye.

In the days and weeks directly after launch, yes, particularly when they're illuminated in direct sunlight at their altitude and where you're standing on the ground the sun has just set.

https://findstarlink.com/

search youtube for "Starlink train" for some good examples.

Last year we got up at 4am to view a supposedly-spectacular comet. Or meteors, or something. It was cold and we lay in the garden for the best part of an hour. We saw nothing.

Just as we were about to give up, I saw a satellite. I pointed this out to my partner. Cool.

And then we saw another ... and another ... and another! Turns out one of the Starlink launches had just happened. We must have seen 30, 40 satellites cross the sky. As each one reached a point, the angle produced a spectacular flare. We couldn't have been luckier.

My partner said that this is what it'll look like when humans evacuate the planet. It was amazing.

(Note: I have very mixed feelings about Starlink and am genuinely worried about the Kessler syndrome. But that doesn't take away from the visual effect.)

Starlink's orbit will be cleared after 5-10 years due to drag on the relatively low altitude. Low risk of permanent Kessler syndrome there.

It's ~5 years for intact satellites to deorbit from Starlink's altitude. Debris will generally have a higher surface area to mass ratio due to the square-cube law, so should experience proportionally higher drag force and deorbit somewhat faster. But the real key is that debris doesn't have to deorbit all the way to stop kessler syndrome, it just has to get a few km down below the orbits of active satellites, which will be much less than 5 years. I believe it would be difficult to trigger Kessler syndrome even intentionally at that altitude.

Yes, usually easier near sunrise or sunset if the angle allows sunlight to reflect back to you. ISS is also a bright object that can often be viewed one a week or so if you are willing to be awake at the right time.

Not exactly "easier". These two time windows are the only times you can see satellites. The rest of the night there's no sunlight falling on satellites when they are in line of sight to you.

In a dark place you can see a whole lot more than that with the naked eye, including some distant galaxies.

> including some distant galaxies

"Distant" only in the sense that all galaxies are distant. You can see Andromeda and the Magellanic Clouds with the naked eye. You can see the Orion Nebula (but that's not a galaxy). There might be a handful of other nearby galaxies that you can see with the naked eye, I don't know.

If it’s dark enough Triangulum is naked eye visible too. Sure those are all in some sense local, but it’s still neat to see almost three million year old light.

I only had chance with monoculars but that is exciting as spotting in the supposed position through the lens and tracking the fast moving dot in front of the stars (amplified by the magnification) turns into a high speed chase.

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