Here’s a nice little article and video from the BBC website about the astronauts currently repairing, and replacing and installing components on the Hubble Space Telescope. Imagine how careful you’d have to be when designing a computer system that could be put out of operation for five years by a power failure, because you have to go to space to fix it!
The Big Picture also has some great pictures of the mission.
This is the brilliantly-named Sombrero Galaxy, about thirty million light years away in the constellation Virgo.
The Sombrero Galaxy. Click to enlarge. Credit: Nasa and Hubble
The beautiful dark bands around the rim of the ’sombrero’ (and visible in much more detail under magnification) are dust lanes: great elongated clouds of interstellar dust mixed in with the gas in the galaxy. They’re dark because the dust absorbs light well: interstellar gas, although there’s a lot of it in a galaxy, is made up of atoms too small to have much effect on visible light passing through - but these little dust grains maybe a hundredth or a tenth of a millimeter across are the right size to absorb or scatter light.
Here’s a video instead of the usual picture: Space Shuttle Atlantis launching yesterday to head to the Hubble Space Telescope, the machine responsible for many of the other pictures on this blog. Make sure to watch up to the release of the booster rockets which fell back to Earth.
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Light, like sound, is a wave. Sound waves are caused by vibrations in the air (or another medium) transmitting energy: if you sit at a single point in the path of a wave and measure the pressure of the air, you’ll see it fluctuate up and down as the wave passes. With light the medium is the strength of the electromagnetic field instead of air pressure, but the principle is the same.
A wave progressing: the points at which the blue dot is at its highest are a set of wavefronts. The height of the dot could represent local air pressure for a sound wave or local EM field for light.
You can think of a wave as being made of a series of ‘wavefronts’ which are emitted from a source and move along in the same direction. For example, all the points at which the pressure is at a maximum make a set of wavefronts for a sound wave. For a simple wave they all move along in a row, all separated by the same, constant distance. This distance is the wavelength of the wave.
Now imagine that the source of the wave is moving away from you. Between emitting one wavefront and the next it will have moved a little distance, and the second wavefront has slightly further to travel. That means it reaches you later than it would have done otherwise, and the wave gets spread out: its wavelength increases. Move the source towards you instead and the opposite happens: the wavefronts get ’squashed’ together and you see a shorter wavelength.
