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Friday 3 April 2020

Satellite spotting!

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Hey everyone, our usual round up 0f the week's space news will be up within 24 hours - we're just waiting on the preliminary results on the failure of SpaceX's SN3 prototype rocket. For now... 

This week has been an interesting one in the UK, and for a nicer reason than Corvid 19. Both the latest batch of Starlink satellites and the International Space Station are visible in our skies. So, since so many of us are cooped up at home, I thought I'd take a quick look at the my personal favourite nerdy pass time: Satellite spotting.

People often start with this one.

Now, as geeky pastimes go, this is up there. Train spotting... pah, those guys are practically cool. But it's surprising how easy it is to do: You need a dark sky (wait until the Sun has been down for an hour and a half, two if you can), your latitude and longitude, one of the websites listed below, and a bit of basic knowledge of how to read a star map, (like what magnitude numbers mean) Put your position into the websites and they will return a list of times various satellites are predicted to fly over, as well as a map, showing the path the object will take.

For satellite and spacecraft predictions I use Heavens above or In-the-sky. Those are my favourite two - I usually double check them against each other. - but there are others

That sounds fairly simple, but with modern skies it can be challenging: A lot of these satellites are odd shapes, and their orientation is unknown and changeable.As a result by the website's own admission the brightness values they give are an educated guess at best (for reference, with a really dark sky the human eye can pick up a magnitude 6 star, with most modern skies you're looking at magnitude 3 at best) And you're hard put these days to find a sky that isn't light polluted to some degree. If you're under urban or suburban skies I wouldn't bother with anything below magnitude 2 (about as bright as the pole star), but that usually still leaves you with a couple of satellites to try for a night. For a map of where dark skies can be found try this link. 

A real challenge - needing binoculars or a telescope - are geostationary satellites, which are much further away than other satellites (36000km) and only move slowly against the background stars. 

Geostationary satellites caught using time-lapse photography

Once people have a bit of experience under their belt, and especially if they're into other areas of astronomy, they often go for trying to catch satellites in their telescope, and even photograph or record them. That can get fairly involved, but with practice you can get some fairly impressive images - most people start with the International Space Station...

The International Space Station. Video taken through a 20cm Dobson telescope with a tracking mount, and sharpened by frame stacking. Courtesy of Silwyna via reddit 
With practice, a big amateur telescope (the kind an astronomy club might pool their resources for) , and some imaging techniques like 'frame stacking' the images can be quite impressive, rivalling those taken by other spacecraft:

Image of the ISS taken with an 8″ diameter Dobson telescope, a high-speed monochrome camera and manual tracking.

The ISS seen using a 64 cm diameter telescope, by Don Kantowitz and Marek Kozubal. Courtesy of the Clay Centre Observatory at Dexter and South field schools. 

In the days of the Space Shuttle and Mir they were both frequently imaged by enthusiastic spotters:

A Space Shuttle in orbit, raw picture on the left and electronically sharpened version on the right. 

The Space Shuttle Atlantic docked to the Mir space station

It's a hobby that has been going on for a while - these images were taken by an amateur of the Apollo 8 mission, as it fired it's engine to leave Earth orbit and head towards the Moon...

Some of the more challenging targets for close up imaging are, surprisingly, those in the nearer, low Earth orbits (which, ironically are the easiest to find with the naked eye). LEO satellites cross the sky faster, and are much smaller than the shuttle or any space station. But it can be done (and is daily) and among satellite spotters Thierry Legault is one of the best known for it, taking images of satellites like Lacrosse 3...


... and for really hard bitten veterans, there's the challenge of hunting down classified satellites that don't appear on the databases: Here a US Keyhole spy satellite has been on camera:

Here're two angles on the classified USAF X37-B mini shuttle, courtesy of Ralf Vandebergh..

That's a quick run down of this very 21st century nerdy hobby - which is also a very satisfying one, when you finally track down a hard to spot satellite, or see an event like a flare (where a satellite spikes in brightness as the Sun hits it at the right angle). At the highest end it's almost international intelligence gathering, as you track classified spacecraft. But for me, under lockdown here in Scotland, it's a reason to get out in the garden and enjoy the stars... when there's a break in the clouds! It all adds to the challenge... 

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