SEEING SATELLITES

by Terence Dickinson
SkyNews Editor

Any clear evening this summer you can catch a satellite. Just watch the sky for the first hour after the stars become visible at dusk and you’ll see several steady, starlike dots march across the constellations.

One could be the International Space Station, another a military spy satellite, a third simply a spent rocket still in orbit. A satellite easily visible to the unaided eye is typically 200 to 400 kilometres up, travels at 28,000 km/hr and crosses the sky in two or four minutes.

With a little experience, distinguishing a satellite from an airplane is easy. Most aircraft have either flashing lights or red or green wing lights, though a few have a steady white light like a satellite. Binoculars usually reveal engine exhaust or other lights on planes that appear to the naked eye as single white lights. Satellites always appear starlike but untwinkling.

Satellites are made visible by sunlight shining on their metallic surfaces. As a satellite changes orientation with respect to the observer as it passes over, its brightness can surge for a few seconds because of direct reflection of sunlight from a solar panel or other flat surface. If the satellite fades and disappears as it cruises across the sky, it has entered the Earth’s shadow. The Earth’s shadow climbs higher as the sun sinks lower, which is why the best time to scan for satellites is the first hour after darkness falls.

Well away from city lights, an observer on a careful watch should see a dozen or more satellites in that first hour. The number drops after that and is quite low around midnight or 1 a.m.

Even more interesting is watching for specific satellites. By far the brightest is the International Space Station (ISS). On the evening of June 17, a few days after the space shuttle Atlantis astronauts had installed a huge new solar panel to increase the electrical supply for the station, the ISS made a perfect overhead pass over my home in eastern Ontario. As it passed over, its brightness ranged from magnitude -1 to a dazzling -5, slightly brighter than Venus. It shone with a golden glow, reflecting the colour of the solar panels which now account for most of its brilliance.

When will the ISS pass over your town? An excellent website that will tell you is www.heavens-above.com. Once you are there, take a few minutes to register. It’s free, and it will make your future visits faster and more enjoyable. Not only will you learn which satellites are passing over, you also will get times of sunset, sunrise and twilight, phases of the Moon, constellation maps and much more. The best feature is the sky map showing the path of the ISS (and other satellites) through the constellations for your site.

The ISS is visible from any given site for a few weeks at a time, then is unfavourably positioned for a few weeks, then visible again, in a repeating visibility cycle. Overhead passes are the brightest because they closer to you. In the case of the ISS, the altitude of an overhead pass is about 400 kilometres.

How much stuff is up there? The U.S. Air Force Space Command operates telescopes on the Hawaiian island of Maui and other strategic locations to track working satellites as well as the orbiting junkyard of defunct satellites and rocket casings. They keeps tabs on more than 12,000 objects ranging from van-sized communication satellites to a hatch hinge the size of a cell phone that broke away from a European satellite’s covering in 1988. Less than 1000 orbiting objects are doing anything useful, the rest is rubbish accumulated since the dawn of the space age nearly half a century ago.

Everything larger than a walnut flying in low orbit—200 to 400 kilometres above the Earth—is monitored along with all objects larger than a baseball out to geosynchronous orbit at 35,900 kilometres, where a fleet of communication satellites is stationed. The trajectory of the space shuttles are regularly altered to avoid a close brush with any of these potentially lethal chunks.

CELESTIAL OBSERVING TIPS FOR JULY 2007

by Todd Carlson
Assistant Editor

Although summer is a time when vacations can mean more time to observe the night sky, recreational astronomers have to contend with long days and short nights. The first rule of summer stargazing is remembering to bring along binoculars. Binoculars can reveal star clusters, dozens of craters on the Moon and up to four of the moons of Jupiter. Steady the binoculars by leaning against a wall or propping your arms on a picnic table or fence.

In order to make the most of the short July nights, here are the celestial highlights for the month.

1) Mid-July presents the best opportunity of the month to view deep into our own galaxy, the Milky Way. Looking high in the east after 11:00 p.m. from a dark site, you should be able discern a hazy swath of the Milky Way cutting towards the southern horizon. Use binoculars to examine the section towards the southern horizon where you should notice the density of stars increasing. That’s where the centre of our galaxy is located.

2) July 15-17. Watch for Earthshine, the portion of the Moon illuminated by light reflecting off of the Earth. Binoculars enhance the view. The Moon will be near Venus on July 17th.

3) All month: Jupiter can be found rising in the southeast after sunset and appears as the brightest "star" in that area of sky. Jupiter, the largest planet in our solar system, has a family of 63 moons, four of which can be seen in binoculars—Ganymede, Callisto, Europa and Io. Depending on the position of each moon during its orbit, observers may see two, three or all four moons on a particular night.

4) All month: Ursa Major, the Big Dipper, rides high in the northwest once darkness falls. The constellations Sagittarius and Scorpius can be located in the south. An unobstructed southern horizon is essential for viewing both.