viewing is an easy skill
to pick up in amateur astronomy
, and requires little or no equipment
. It's also fun and does not require one to stay up late at night, since most satellites are visible
only in the early evenings (or mornings, if you are inclined to get up before everyone else).
What are satellites?
The Earth has two different types of satellites: a natural
satellite, our Moon; and artificial
satellites. Satellites are objects which orbit a larger body, like the Moon which orbits the Earth.
Due to the rapid
) advancement in technology in many countries, there are now countless
artificial satellites orbiting our planet.
Purposes of satellites
These are various
uses of satellites:
Space Telescope (HST) and International Space Station
(ISS) are just about the brightest satellites that one can see in the sky.
The Global Positioning System
(GPS) has 24 satellites in orbit currently. These help a person on earth determine where he/she is at any given moment.
3) Earth-monitoring sytems
Upper Atmosphere Research Satellite (UARS) and SeaSat 1 (monitors ocean current
s and temperature
) are some of the satellites that help geologist
s and weather-forecasters do their job.
For satellite TV
, for example. Also includes ham radio satellites, like the Oscar satellite
5) Classified information
This list is not exhaustive. There might be some other uses of satellites that I'm not familiar with, or plain forgot about.
Best time for viewing a satellite
The best time for viewing satellites is in the wee hours
of the morning before dawn, or just after the sun sets. This is because the sun is still below the horizon
for the sky to be dark, yet not too far below the horizon for the satellite to catch and reflect the light back to Earth.
As satellites move pretty quickly (they orbit the Earth about 14 times a day, on average), it is important to have accurate
timing as there is only a short window of time (about 10 minutes) to view them.
How bright can satellites get?
This depends on the size and "reflectivity" (ability to reflect) of the satellite. Like stars, this means that not all satellites are easily seen. A pair of binoculars
or a telescope
can help in viewing a faint satellite.
As far as I know, some of the brighter and more well-known satellites are the International Space Station (ISS) and the Hubble Space Telescope (HST), both of which can reach about magnitude
3 or 2 at least (quite visible with the naked eye - the brighter the object the lower the magnitude).
Of course, there are also iridium
flares. This is caused by the light of the Sun being reflected by the antennae* of certain satellites. An iridium flare can reach negative magnitude, and even be brighter than the planet Venus (magnitude -4, which is *very* bright). However, they last only for a moment.
Conditions needed for viewing satellites
A clear, dark sky is ideal for viewing satellites and their flares; however, people have viewed satellites in broad daylight before. Just be careful NOT TO POINT YOUR BINOCULARS OR TELESCOPE AT THE SUN AND LOOK THROUGH IT. I strongly recommend naked eye viewing in the daytime.
Equipment needed for viewing satellites
A whole sky map
comes in handy to identify the constellations.
is needed if you're not sure if the direction you're facing is the right one. If you need to determine your coordinate
s precisely, a handheld GPS system is needed.
A watch is essential as satellites wait
for no man. Tardiness means that you might not get to see your satellite.
Binoculars are useful to zoom in on the satellite, especially if its just a faint speck
(the sky may not be completely dark, so it might be difficult to view them with eyes alone). Telescopes are optional. The trouble with a telescope is that if you're not familiar
with it, and have to fiddle about a lot with it, the satellite might just disappear from sight before you can view it properly. But if you're expecting an iridium flare, please TRY TO VIEW IT WITH YOUR NAKED EYES. Otherwise you might suffer from temporary blind
ness after viewing an extremely bright flash of light in a dark environment, when your pupils are dilated
Lastly, you need to know the time that a satellite will pass by your location, and the direction in which it would appear. As satellites move much more quickly than stars, there should be no problem distinguish
ing them from stars if you are stationed at the site before it appears, and watch carefully for any "abnormal
star" that appears. You can get information about satellite passes from http://www.heavens-above.com/ . More is covered in the next section.
Information needed for viewing satellites
1) Know thyself...
Coordinates are needed to know when you can expect to see a satellite. For a general view of a satellite, Heavens Above (http://www.heavens-above.com/) recommends coordinates within a 10 km radius. For iridium flare viewing, coordinates within +/- 1 km are best.
2) And know thy satellite...
from which the satellite is approaching, the duration
of the pass, and the magnitude
of the satellite will help in its identification. Otherwise you might mistake it for just another star... until you realise that its going past too fast. Oops! Bye!
If you're interested in finding out more about satellite viewing, I recommend the following sites:
Heavens Above! - http://www.heavens-above.com/
This site is great! It has a large database
for coordinates all around the world, even a small country like Singapore has several places listed.
Iridium Flares - http://www.satobs.org/iridium.html
About how and why iridium flares occur
Google - http://www.google.com
This looks dumb, but everything I learnt about astronomy (especially the minor branches of it), I learnt from Google searches.
Iridium flares are caused by reflection off a teflon
-coated aluminum panel of an Iridium satellite--Iridium is the name of the satellite, not the material it is made from. The flare can last 5 to 20 seconds--really impressive if you've seen one.
One final nitpicking--if you have a star map, a compass seems superfluous, unless you are just starting to learn the sky.
Thanks also to wertperch and lj, who corrected me when I wrote that satellites orbit the Earth "14x times on average". The satellites orbit 14x a day on average, not just 14x.