It is a wonderful thing that our world has a nice, dense atmosphere. Without it we would not be here.
However, it does not make life easy for astronomers. Apart from cloudy nights where only our radio telescopes can see out into the universe, instability in the atmosphere makes stars romantically twinkle, which manifests itself through our telescopes as images dancing around, flashing with spurious colours and hiding their detail.
Then, finally the atmosphere only lets in certain wavelength ranges. It is transparent to visible light and a large part of the radio spectrum. It blocks almost everything else.
This is again something that is good for us because dangerous short wavelength ultraviolet radiation and X-rays get almost totally blocked, as do high-energy particles.
It is still worth building telescopes on the ground because they can be bigger, more flexible and relatively cheap. We like to put our optical telescopes on mountain peaks surrounded by stable air. However, for seeing exceptional detail without the atmospheric shimmering, or to observe wavelengths that don't reach the ground, there is no alternative to putting telescopes in space, orbiting above the atmosphere.
This was the reason for launching the Hubble Space Telescope. The HST was launched in 1990 and is still in orbit doing science. It has a 2.4-metre diameter mirror, which is relatively small compared with the mirrors on ground-based telescopes, which are now getting into the 10-metre to 30-metre range.
The mirror on the HST was limited by the telescope having to fit into the cargo bay on the Space Shuttle, which is what was used to lift it into orbit. Since it was launched, the HST has justified itself many times. The images it sent back have been stunning and scientifically exciting.
Of course, every new view of the universe provides new questions. A lot of interest is now focused on understanding the early youth of the universe.
The Hubble Space Telescope continues to be a valuable scientific research tool but to look at the early universe, and especially the birth of the first stars and galaxies and seeing what they were like, we need a new and more sensitive instrument. That instrument is the James Webb Space Telescope, which is currently under final preparation for launching Dec. 18.
The JWST is a joint project of the U.S., European and Canadian space agencies. Thousands of scientists and engineers are involved —some as employees of those space agencies and others distributed among some 248 companies that are contributing to the project. It is to be launched using one of the European Space Agency's Ariane 5 rockets.
This telescope has a 6.5-metre diameter mirror, much larger than the mirror on the HST and should collect much more light. This has been a challenge because there is no way such a large mirror will fit inside the launcher. So the mirror has to fold up.
It is therefore made up of a number of hexagonal panels. When in orbit this has to unfold into a perfect mirror. The detectors on it have to be kept very cold in order to operate with their best sensitivity. In space things naturally become very cold providing the Sun is not shining on them. So the JSWT is to be parked at a stable, Lagrange Point, where it remains permanently in the shadow of the Earth.
In addition, it has complex sunshades to keep away stray sunlight or heat from the Earth.
So astronomers around the world are looking forward to a wonderful Christmas present that will tell us more about the processes that gave rise to the universe, and us.
Once in orbit, the antenna and sunshades have to be deployed and this complex telescope set up, tested and calibrated. Only then can the science start.
• After sunset, Venus lies close to the southwest horizon.
• Jupiter and Saturn are low in the southern sky. Venus shines brighter than Jupiter, with Saturn a lot fainter.
• The Moon will be full on the Nov. 19.
This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.