Observing Satellites

In 2001, I took up satellite watching after discovering an amazing website, Heavens Above.

On that website, you get predictions of passes of a large number of visible satellites, from the huge International Space Station and other bright satellites, such as the Hubble Space Telescope, through to barely visible obscure satellites, spent rockets and debris. There are also predictions for the spectacular Iridium flares (see below).

I go out to watch the satellites with:

• A print out of the night's pass predictions and a sky chart (from the Heavens Above website),
• A compass,
• A small torch (with the light lens covered with red cellophane) to read the predictions and to watch the time,
• A fairly accurate digital clock with seconds.
• A pair of 10 x 50 mm binoculars (lower magnification will do)
• A pen to tick off the satellites and to write down comments.

Satellite watching can be frustrating. Cloudy skies, bright city and suburban lighting, and a full moon can spoil a night's viewing. Sometimes, you are just not quick enough and the satellite has gone before you fix on its position.

Many satellites that are on Heavens Above's prediction lists are visible to the naked eye, but binoculars come in handy for some of the fainter ones. You do not need a telescope and, in fact, satellites are moving far too quickly for you to track them with a telescope.

Find a comfortable safe spot, as far away from lighting as possible, and with a clear view of the night sky. Some back yards are not suitable and you may have to travel to another more appropriate place to obtain better viewing conditions. Allow your eyes a few minutes to become accustomed to the dark.

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When to see satellites

Satellites are usually only visible from about half an hour after sunset for about two hours. To see a satellite, you must be in darkness and the satellite (many hundreds of kilometres above) must be in sunlight (see pictures below). Satellites can also be viewed prior to sunrise. Each satellite is visible for a matter of minutes as it moves quickly across the sky.

Photographing Satellites

It was only a matter of time, before I decided that I also wanted to keep both a written and photographic record of my satellite observations.

In my travels through various satellite watching websites, I came across photographs of satellites, in particular the Iridium flares, which are the most interesting and eye-catching satellites to watch and photograph.

For satellite photography, you need:

• A reasonable quality SLR camera.
• A tripod is essential.
• A shutter cable may also be useful, but is not essential.

Fully automatic cameras or cheaper digital cameras (without manual features) will not work as you will need to manually control the aperture and the exposure time.

I use a relatively cheap Nikon F60/N60 with a standard 35-80 mm lens. I have recently purchased a 70-300 mm lens for some closeup photos. The lowest f-stop that I can use with this camera is only f4 whereas f1 to f2 is more commonly used for this type of photography. For best results, the largest aperture should used and the exposure times can be varied depending on the circumstances.

I am still experimenting with exposure times. The maximum timed exposure with a Nikon F60 is 30 second exposure. This seems to be a little too short with an f4 aperture. I have been trying some longer exposures. One minute is suitable for the brighter satellites and up to two minutes for dimmer ones.

When you get your photos developed, make sure to tell the processing centre that photos are night shots of satellites, otherwise they will think that they are just black and will not process them. Also asked them for gloss finish rather than matte, if you are planning to scan them on a flat bed scanner.

Here is a link to a Dutch language site on satellite photography by Niels Buikstra.

Iridium satellites

The Iridium satellites were launched by Motorola in 1997 and 1998 and were designed to allow the use of satellite phones anywhere in the world. They are especially useful for those in remote areas or at sea.

It was originally planned that there be seven planes with eleven satellites, each circling the earth via the poles. Some failed, some went out of control and are tumbling around, and some have reentered the Earth's atmosphere and have burnt up. Some new ones were launched in February 2002.

They are not made of iridium, but are named after the element, because the iridium atom has 77 electrons circling the nucleus and there were to be 77 satellites circling the Earth. However, there are now only six planes with 11 satellites each (plus some "spares".)

Their three Main Mission Antennae (see right) are made from highly polished aluminum and are about the size of a house door. When they reflect light from the Sun, an observer in the correct position will see a bright flash or flare in the sky for several seconds.

This flare is often many times brighter than the brightest planet, Venus (magnitude* -3 or -4). Flares reach magnitudes of -8. On occasion the brightest flares can be seen in the daytime!

Here is a link to my list of iridium satellites.  This lists all the Iridium satellites that have been launched, including the non-operational ones and those orbits have decayed.

Magnitude

Magnitude refers to the brightness of space objects. The brighter the object, the lower the magnitude. It is a logarithmic scale, so that a difference in magnitude of 5, means an object is 100 times brighter. A difference of one magnitude, means that it is 2.5 times brighter.

Some examples (from Heavens-Above):