Satellites
Once you get into going out in the evening looking at Stars,
Planets, Meteors and the Moon, you may notice that there are other things
cruising through the sky other than objects 100,000 kilometers and more away.
To turn these “UFO”s into “IFO”s, there are some pretty easy techniques. And
then, you can go even farther!
At any given time, there are several thousand objects orbiting the
earth. These vary in size from baseballs to schoolbus plus. Some are active
working satellites, HST and ISS are big and bright, and others are fragments of
rockets, or trash thrown out of ISS! There are 100 or so reasonably bright
satellites that are visible, though you won’t see them all in one night. All of
these easily visible satellites are Low Earth Orbit satellites (LEO), staying
between 150 and 800 kilometers above the Earth’s surface. Orbital mechanics
means that they may not be passing overhead where you are during the crucial
“satellite hours”.
Satellite hours – If you head outside for the hour or so
after sunset, or the hour or so before sunrise, you stand a good chance of
seeing a satellite or 5. My best was 10 in and hour and a half. It’s a simple
process, go outside and look up! Give yourself time to dark adapt, and enjoy
the sky even if you don’t see one! For best results you will need to aim your
attention in certain directions, and that is based on typical satellite Orbital
Inclination.
Orbital Inclinations – There are three basic pathways used
by most of the LEO satellites. These originate in the purpose of the satellite,
and the location of the launch. Early American satellites were launched
eastward in 23 degree inclination orbits (23° to the equator) from Cape
Canaveral, since that was the latitude of launch. Early Soviet satellites were
launched eastward at about a 56 degree inclination (56° to the equator), again,
the latitude of the launch. Finally, most Earth Resources, Weather, and Spy
Satellites were launched in “Polar orbits” of roughly 98°. When put into the
proper altitude, this made them “Sun Synchronous” – going over the ground
at the same sun angle each time.
What this means for satellite watching is that all satellites are
going to be going in 4 basic directions.
1 – North to South
2 – South to North
3 – Southwest to Northeast
4 – Northwest to Southeast
Most satellites will look like stars crossing the sky at a steady
pace. A few will be tumbling, and so catch the sun in different ways, flashing
their way across the sky. Of course, if you see a red flashing light crossing
the sky, it is likely to be an aircraft! If you have binoculars, look for the
additional green and white lights. If it is moving towards the west, it is most
likely an aircraft also!
Most satellites will be “white” in color – however a few
have been seen to have a yellow-orange color. These may be fuel tanks, and
there is some discussion that they may also be spy satellites. The ultimate in
satellite light comes from the Iridium satellites, when light from the sun
flashes or flares from one of the solar panels.
Iridium Flashes – These are lots of fun, but you have to
have your watch set accurately. They only last about 15-20 seconds, and can be
up to a magnitude -7 if you are in the right place on Earth. The best way to
find out about them is using the “Heavens-above” website. Enter in your
latitude and longitude, or city name, and ask for a weeks worth of Iridium
flashes. Go outside a little before the flash is to occur and look in the
general direction of the flash. “Heavens-above” will give you an azimuth
(degrees around from North) and an elevation (degrees up from the horizon).
Keep watch!
Some people have seen these during the day, and I’ve seen them
through thin cloud cover, as well as seeing a thicker cloud cover brighten!
Advanced Satellite topics:
Prediction Programs and Keplerian Elements - Other than going out
and just looking, the easy way to do a serious satellite watch is to make up a
set of predictions. You can do it yourself with software, or have the
Heavens-Above website do it for you.
To do it yourself, you will need two things, a satellite
prediction program, and the latest Keplerian elements. Some of the newer
astronomy programs have satellite tracking built in. Starry Night is one
example. For the Mac – I’ve used OrbiTrak. It is a little dated (originally
system 7! Works in system 8 and 9) and works fine for tracking and predicting.
For Win, I’d do a quick check of www.amsat.org and look under their software
offerings. Some are free, some are old and DOS, and some are shareware.
Keplerian elements? This is the mathematical set of parameters
that give information on the location and movement of the satellites. NORAD
knows where the satellites are, and publishes them (or most of them). If you
have to manually download them, www.celestrak.com is a great source. They also
have a good description of what all the numbers mean. Each piece of tracking
software has it’s own method for inputting the data – that’s where
reading the manual helps J. Newer software will automatically download / update
the elements for you.
Photographing Satellites - Taking pictures of satellites is a lot
like taking pictures of stars and constellations. You need a tripod, a cable
release, and a camera that can be set to “B” to leave it’s shutter open as long
as you need. Using a high ASA film, 30 seconds to a minute will give nice
constellations, with not a lot of star trailing. Some digital cameras can be
set to give a 15 sec to 30 + second exposure. This is something you will have
to read your manual on.
Set the camera up on a tripod, aim it towards the area the
satellite is going to be passing through. If it is going through a nice
constellation, all the better! Set the focus on infinity, the f-stop one down
from all the way open, and the shutter speed set to B. The cable release is a
useful tool to minimize the shaking given to the cameral when you press the
shutter. When the satellite is in the field of view, open the shutter and hold
it open for 30-60 seconds. When the film is developed, there should be a nice
streak going through where the satellite passed.
Iridium flashes are shorter in duration and more intense, so the
use of digital cameras with a 15 second exposure would be great.
Taking pictures of the night sky takes a little practice, but it
isn’t all that difficult to come up with some nice images.
Over the last few years some people have been taking on the
challenge of taking images of the larger satellites as they transit the Sun or
Moon. There are some nice images of the International Space Station and the
Space Shuttle crossing the face of the moon and sun. This requires information
on the exact times and positions of the satellites and the Sun/Moon as well as
taking a picture through a good telescope with the appropriate filters.
Satellite Observations via Radio - Many of the satellites orbiting
the earth carry active radios. With the right equipment, these can be
monitored, and with more sophisticated equipment you can even do some science.
Some of the easiest ones to hear are the polar orbiting navigation satellites,
and many of the amateur radio satellites, including the International Space
Station.
A scanner with an outside antenna will allow listening to many of
these sources. Tune to 150.000 MHz and periodically you will hear data coming down
for 3-10 minutes. If your scanner can tune into the 136-137 MHz band (rare on
the cheap ones), you can listen to the polar orbiting weather satellites. There
are some simple programs that use the soundcard on your computer to let you
display the weather picture in realtime! Amateur Radio satellites are usually
heard in the range of 145.800-146.00 MHz, and it is possible to occasionally
talk with astronauts on the ISS as it goes overhead.
With a more sophisticated radio, you can monitor the Doppler shifting
of the satellite as it goes by. From this you can determine the speed of the
satellite!
If you are quite lucky, you can watch the satellite visually,
while listening to it on the radio. My best was talking to an astronaut on
space station MIR while I was watching it go overhead! WAY Cool!!!
Moving into a more advanced level, some of the amateur satellites
downlink a telemetry set that gives information on the health and conditions on
the satellite. Some years ago a California high school class was able to
determine that one satellite had been rotating on its axis one way, and had
stopped, and started spinning the opposite direction!
Geosynchronous Satellite Observing - While most of the GEO
satellites are large, they are also a long way away – 30,000km +. This
means they are harder to see. Some of the newer computer tracking telescopes
from Meade and Celestron will slew to the satellites in the Clarke Belt and let
you watch them. The cool thing is that the satellite doesn’t move, and the
stars DO move behind them. You should be able to see them in your Dobsonian
telescope, if you’ve calculated where they are and aim correctly.
copyright ted Brattstrom / NEO Foundation 2006
* the following was posted by Ted, Dec. 31st, 1996... we'll add to his list of talents and exploits as we learn more!
High school science teacher - amateur radio operator nh6yk - amateur satellite user - former ATS-3 PEACESAT station manager/operator -
amateur astronomer of the "enjoy the sky and cool faint fuzzy things" sort... and a
few other odd traits... and someone who likes to get people to look up at night, to see the things that are there that they ignore...