The ROSAT X-ray space telescope is due to re-enter Earth’s atmosphere over the coming weekend (22-23 October, 2011). Dr Martin Anderson, Astronomy Educator at Sydney Observatory, writes about his experience using ROSAT.
I was fortunate enough to be part of a space mission aimed at investigating our universe using X-rays. To do this I used a German satellite named ROSAT. ROSAT or Röntgen satellite was named in honour of Wilhelm Röntgen, the scientist who discovered X-rays. Actually, Röntgen was awarded the first Nobel prize in Physics in 1901 for discovering X-rays. To see X-rays you need to be in space as Earth’s atmosphere stops X-rays from reaching the ground. Once launched in 1990 ROSAT was free to observe the X-rays coming from stars and galaxies as it orbited the Earth.
If you’re wondering how the X-ray sky compares to what you see with your eyes then look at the two images below. The first image show how the “Saucepan” in Orion appears in visible light and in X-rays. The second image shows an image captured by ROSAT of the Moon, caused by X-rays from the Sun reflecting off the Moon’s surface.
If you could see what ROSAT sees you would see a night sky filled with a constant glow with a few very bright X-ray sources scattered across it. It would look like the night sky on the night of a full moon with a few bright stars visible amongst the glow. This X-ray glow has been a constant puzzle to X-ray astronomers and is known as the cosmic X-ray background radiation. The brightness of the glow is the same in any direction you look. What causes it and why it is so uniform in brightness is the mystery? One way I tried to answer this question was to select a blank piece of sky and take a very long time-exposure X-ray image with ROSAT to see what the very faintest sources are that emitted X-rays. A region was selected in the constellation of Pavo. With over 20 years of investigation myself and other researchers have found the origin of the glow appears to be the faint X-rays emitted by the billions of galaxies that fill our universe.
ROSAT has continued to orbit the Earth since 1990 but will shortly fall into the Earths atmosphere where it will burn up. This type of event can be very spectacular to a person in the right place to see it. The problem is predicting where it will fall back to Earth is very, very difficult to workout.
If you would like to see ROSAT before it re-enters Heavens-Above predicts when it will be visible from your location. However, the orbit is changing rapidly and the re-entry time and place will remain uncertain until the last few hours. You may want to check @ROSAT_Reentry for the latest information. But don’t confuse re-entry with the shooting-stars of the Orionid meteor shower which is visible after 1-am in the north-east sky from Australia.
Some parts of ROSAT may make it to the ground without burning up. Should we worry about getting hit? Glen Nagle from CSIRO’s Canberra Deep Space Communication Complex has reportedly said, “You’re actually more likely to get hit by a meteor coming in from space than you are being hit by this particular satellite coming down.” I hope he’s right!