October 2011

Time For Satellite Watching

Over the past few weeks I have been going out to one of my favourite deep sky observing locations. I would proceed to set up my trusty C8 (eight inch) telescope and wait for the true darkness of night to fall in order to search for faint nebulae and galaxies. As I waited I would see star-like objects drifting slowly (some quite rapidly) in front of the background stars in the night sky.

The objects I am referring to are artificial satellites in orbit around the Earth. (The Moon is classed as a natural satellite.) Since the launch of the first artificial satellite Sputnik 1 by the Soviet Union on October 4, 1957 there have been thousands of satellites sent into orbit to do a variety of tasks. This includes weather observation (the GOES satellites that Environment Canada uses to observe cloud patterns), communications (IRIDIUM satellite system), research facilities (International Space Station) and specialty satellites (Hubble Space Telescope, military satellites, etc.). There are over 12,000 artificial objects orbiting the Earth at present. Over 2,500 are satellites, operative and inoperative. The remaining objects (estimated 19,000) are orbital debris such as nose-cone shrouds, hatch covers, spent rocket parts, payloads that have disintegrated or exploded and even objects that have escaped from manned spacecraft during operations and maintenance procedures.

Some of these satellites are easily visible to the unaided eye against the dark nighttime sky at the right times. For a satellite to be visible in the night sky it must be illuminated by sunlight, usually at an altitude of 300 to 800 km, while the observer on the Earth is in darkness. The higher the altitude the closer to midnight you can spot them. In fact, during midsummer you can watch satellites cruise overhead all night long. Some would maintain their brightness as they crossed the night sky while others would appear to fade and brighten regularly as they tumbled in their orbit around the Earth.

The two most popular satellites observed are the International Space Station (ISS) and the IRIDIUM satellites. The ISS appears as a very bright star-like object moving slowly (about six minutes during an overhead pass) across the night sky. I have always had an interest in the ISS knowing that when I see it there are usually six people aboard it moving at about 28,000 km/hr at an altitude of around 360 km! At that velocity and altitude the astronauts circle the Earth every 91 minutes and experience 16 sunrises and sunsets each day. The IRIDIUM satellites will appear as a brief bright flare (called IRIDIUM flares) against the night sky background at specific times when their shiny surfaces reflect sunlight directly towards the Earth below. A very popular website www.heavens-above.com can be used to predict when IRIDIUM flares and the ISS can be seen. A few hundred satellites are bright enough to be seen with the unaided eye, but on any given night most either are not above the horizon or passing overhead at night when they are not illuminated by sunlight.

Jupiter rises in the east an hour after sunset at the beginning of October. Its brilliant yellow glow (magnitude -2.9) is easily spotted amongst the much fainter background stars of the constellation of Aries. Jupiter comes to opposition on October 29.

Mars moves rapidly through the constellation of Cancer the first half of October and into Leo for the rest of the month. On the nights of October 1 and 2 the Red Planet can be seen passing in front of the open star cluster M44 (Beehive Cluster) in Cancer. Mars’ magnitude of 1.3 is about 100 times brighter than the sixth magnitude stars of this cluster. For those observers who are up late at night this will be a good photo opportunity to image rusty coloured Mars in front of a nice backdrop of orange, yellow and blue stars of the Beehive Star Cluster.

Clear Skies

Ted Bronson