Darrell Heath
Astronomy Columnist
Think of stargazing and you think about being outside looking through telescopes or binoculars at stars, constellations, the Moon, and planets and such. But there are human made objects to look for in the night sky as well.
By some estimates there are 30,000 man-made objects in orbit around the Earth right now. Some are functional satellites such as those used for communications, weather monitoring, navigation, spy and military operations, space telescopes, and even those large enough to hold a crew of several humans; the rest is “space junk”: defunct satellites and the pieces of rockets that carried them into space.
No optical aid is needed, just use your eyes to scan the sky and look for a faint star-like object moving against the background stars. Within about 15 minutes you should see at least one or two. If you see flashing lights then you’ve spotted an aircraft and not a satellite.
As is the case with most things involving stargazing there’s an optimal time of night and year to observe satellites. The best time to observe them is anywhere from 45 minutes to two hours after sunset or just before sunrise. The sky has to be dark enough to make them visible and yet not so late that your viewing location has passed within Earth’s shadow. During the early evening, or just before sunrise, there’s enough sunlight hitting our atmosphere hundreds of miles above to light up a satellite or piece of space junk. The time of year can also be an important factor. During winter the Earth is in a point in its orbit so that Earth’s shadow is already well overhead soon after sunset, not a good time to see these otherwise faint objects. During summer our orbital position is now such that Earth’s shadow is angled southwards and never quite makes it overhead, even at midnight; summer is prime time viewing season for satellites.
Most satellites you see are going to be faint, just at the threshold of naked eye visibility. Some may be as bright as the Moon or Venus! If your viewing location is optimal you can see anywhere from 10 to 20 satellites an hour.
Satellites are most often seen traveling from west to east and not the other way around. They are launched this way to take advantage of Earth’s 1,040 mph spin rate. Because the Earth spins faster near the equator most launches take place as near there as possible: you get to add more payload for less fuel this way. Occasionally you’ll see satellites heading on north-south trajectories, or vice versa; be sure to smile and wave when you see one of these because it may well be one of those spy satellites I mentioned earlier.
While the majority of satellite sightings are a bit on the dim side there are two that can occasionally shine as bright, or even brighter, than the planet Venus: the International Space Station and Iridium flare satellites.
At 450 tons and bigger than a football field the International Space Station is the largest man-made structure in space, it circles the globe in a Low-Earth orbit 225 miles up every 90 minutes. The ISS is a microgravity laboratory and is occupied by six people at any one time. Over an acre of solar panels extend out to either side of the crew and cargo areas and when the ISS passes over at just the right time and the sunlight hits those panels it can be the brightest object in the evening sky after the Moon. Sometimes, when the ISS is angled just right towards the Sun the station can appear to flare in brightness to magnitude -8; more than 16 times as bright as Venus!
Its orbit around the Earth is such that just about everyone on the planet gets to see it at one time or another, but you’ll have to know exactly when and where to look. Luckily, NASA will send you email notifications as to the time, date, and viewing directions. Visit spotthestation.nasa.gov to sign up. There are even a number of apps that will notify you as to the next flyover.
Iridium satellites are old communication satellites and they are also one of the most dramatic performers you will see in the night sky. Each spacecraft is equipped with three door-sized and highly reflective antenna arrays, during a favorable flyover sunlight will hit them and direct it back to an observer on the ground. This creates the spectacular sight of a dim-looking satellite suddenly flaring in brightness; so much so that at times it can become 25 times brighter than the planet Venus! Check with Heavens-Above.com for flyover times and, yes, there are even apps for that as well.
While you are gazing up and looking for these moving dots of light in the dark here is something to think about.
The furthest a human being has traveled in space is when the crew of the ill-fated Apollo 13 mission used the Moon’s gravity to help slingshot them back safely to Earth. At the farthest they were 248,655 miles away: no human has ever been more distant. The furthest a man-made spacecraft has ever been is the Voyager 1 space probe, currently 11 billion miles away, within the edge of interstellar space. The closest star system to Earth is Alpha Centauri, some 4.3 light years away. Traveling at the speed of one of NASA’s retired space shuttles, say 17,600 mph, it would take you 165,000 years to reach Alpha Centauri. While those satellites appear to be very distant the truth is that we have just barely dipped our toes into the great cosmic ocean.
Darrell Heath works at the University of Arkansas at Little Rock and is a producer and host for the UALR Television show “The Night Sky.”
