Photographing The Iss
As a twist on the classic phrase, the International Space Station (ISS) is occasionally described as the only man-made thing in space that is visible from the Earth. It's only visible under certain conditions, but when it is you can just step outside, look up, and watch it pass overhead. And while you're at it, why not take a picture?
If you haven't tried photographing the stars then you should do that first. The method for photographing the ISS is essentially the same, but with a few added difficulties:
- Spotting it: Although there are lots of opportunities to see the ISS, there are a few things to bear in mind. Firstly it will only be visible during the conditions of dusk and dawn (explained below), and even then only for a few minutes on certain dates/times . Thankfully there are lots of places to check information so that you're not disappointed. There is an official NASA site, but for the UK the Meteor Watch site picks the best chances and provides lots of spotting/photographing tips. There are also quite a few smartphone apps that can make things much easier - even giving you the direction to look-in - just search your relevant store.
- Limited window: Each pass of the ISS will only be visible for a few minutes (typically 1 - 4). Sometimes there might be two passes in an evening/morning, but they'll be around an hour and a half apart. To begin with you can wait for a long pass, and try a few 1 minute exposures.
- Changing conditions: Because you'll be standing there at dusk/dawn the lighting conditions will change. It isn't a massive problem, but it can make it a bit trickier to work out what camera settings to use.
The International Space Station always moves from the West to the East. Exactly where in the sky it will appear or disappear will vary each time, but the sites listed in 'spotting it' above will give you a clue. Some of the available apps will point you straight to it. It could be described looking like a fast moving star, or a plane that isn't flashing, but in all honestly you should easily recognise it when you see it.
The image below shows the sort of image you can expect just from standing in your garden and taking a 1 minute exposure (assuming there's a clear sky).
If you look closely at the top-right then you will notice a kink. This wasn't a sudden change of course, it was a wobble caused by pressing the button on the camera. You can avoid this by using the count-down timer available on most cameras - you only need a couple of seconds.
There's not doubt that there is a certain amount of satisfaction from having photographed the ISS; but if you were just pointing the camera at the sky then it won't be the most interesting picture. Once you're comfortable with the basics then you can be as creative as you want. Angling the picture so that you get some roof-tops or trees in the shot can add some interest, and make it more obvious what it's a picture of.
Why Only Visible at Dawn and Dusk?
Both the Earth and the ISS are rotating in the same direction (CCW when viewed from the North Pole), although the ISS is rotating much faster. In order to see the ISS there are a number of criteria that need to be met (also shown roughly in the diagram below):
- The sky needs to be dark enough for the ISS to stand-out against the sky (e.g at the point marked "You Are Here").
- The ISS needs to be passing overhead, but not in the Earth's shadow, and at an angle where you can see the Sun's light reflected off of the solar panels.
When (or if) the ISS passes into this window of visibility determines how long you see it for.