How to See Satellites and Other Spacecraft
Tips on Observing Man-Made Objects in the Sky
Beginning stargazers have probably already seen satellites as they silently pass overhead, they just might not know what it was they were looking at. On any given night, satellites and other spacecraft are sailing across the sky every few minutes. Simply spend a long enough stretch outdoors under dark skies, looking overhead, and you will soon see what usually appears to be a dim star, gliding slowly among the stars and through constellations from one end of the sky to the other. Satellites do not have blinking lights or make noise and, except for a few cases, they generally remain dim points of light.
How to Pinpoint When a Satellite Is Passing Overhead
Various online programs are available to help observers time just when specific objects are going to pass through their area. One of the most popular is Heavens Above. It allows an observer to input their location and get a list of objects that can be seen. It also allows you to look back at previous days in case you have seen something and are curious as to what it is.
Some of the spacecraft that they track, besides general satellites, are the International Space Station, the Hubble Space Telescope, and Envisat. When the space shuttle is orbiting they also have data for its passes as well. The information given includes the date, the time that the object will appear, reach its highest height above the horizon, and disappear. It also tells you how bright the object will be (lower numbers meaning a brighter object), which direction to look in (SE, WNW, etc.), and how high the object will be from the horizon (10 degrees is just above the horizon, to 90 degrees, which is straight overhead).
How to Know What Spacecraft Is Visible
Clicking on a daily prediction gives a list of satellites visible for the coming evening. The name of the item, such as a spent rocket, is listed, with a link that will access information such as its launch date and its known orbit. The link under the object's time leads to a very helpful sky map that shows the stars and constellations the object will be passing.
The Brightest Satellites: Iridium Flares
The best type of satellite to observe are those in the Iridium constellation. This fleet of communication satellites produces a short-lived but intense brightening. Iridium flares, as they are called, can reach magnitude -8 at their peak, briefly becoming brighter than any star, planet, or satellite in the sky. Flares can even be bright enough to be seen during daylight.
Why Can We See Satellites?
Satellites are visible to observers on the ground because they reflect the sunlight. In the early evening, after the sky has grown dark, the satellites that are high above Earth are still bathed in sunshine. The same thing is true in the morning. While the sky is still dark but before the sun has come over the horizon, sunlight is already shining on the spacecraft above Earth and making them visible. This is why, in the deepest parts of night, satellites will not be visible. There is no sunshine hitting them at those moments.
The Hubble Space Telescope Can Be Seen from Earth
|
What do you think about this article?
More in Science & Nature
Latest Articles