Edwin Hubble-The Greatest Astronomer of all Time? Part 2

So far Hubble had proven that there are galaxies outside the Milky Way. Much more was to come from this remarkable astronomer.

He was also observing more distant galaxies, and by looking at the redshift in their spectra, working out that they are moving away from us. He also calculated that the further away they are the faster they are moving away from us. The Universe was expanding at an accelerating rate. Hubble calculated the ratio which determines the velocity at which galaxies are receding from us. I will call this ratio the Hubble Constant but it has other names such as the Hubble Flow. Its current value is calculated to be 74/km/s/mparsec. (A different calculation put the figure at 68). Either way that’s a mighty big figure, but we are thinking about the expansion of the Universe! Mparsec means a million parsecs, which is about 3,260,000 light years. The ratio means that for every mparsec for the observer the velocity recession of objects at that distance increases by 74 (or 68) km per second (about 160,000mph). It’s hard to get your head around it. In simple terms the Universe is expanding and the further away objects are the faster they are moving from us. The Hubble Constant tells us the rate at which this is happening at various distances but also allows us to work backwards to calculate when the expansion must have started- i.e. when the Big Bang took place. The latest figure for this event is 13.8 billion years ago. Another big figure. Whilst we talk about galaxies moving away, in fact, what is happening is that space itself is expanding. Another hard concept to grasp. Some galaxies such as Andromeda are not moving away from us despite the expansion of space, because of the effects of gravity over relatively small distances in space. In fact, Andromeda is moving towards the Milky Way and in the far distant future they will merge.

The Hubble Space Telescope was launched by NASA in 1990 and has been a phenomenal success. Part of its function was to make better observations of distant galaxies to establish more accurately the Hubble Constant. The telescope was not just named after Hubble, but was also intended to carry on his work. After Hubble’s discoveries our view of the Universe could never be the same as it was.

Hubble is also famous for his classification of galaxies. But that’s a long story.

An interesting fact is that before he took up astronomy as a career, he was a successful amateur heavyweight boxer and was asked to turn professional. We should all be glad that he turned down that offer.

Hubble could not rely on Cepheid Variables for his observation of far distant galaxies, because they could not be identified beyond about 100 million light years. They are described as “standard candles”, because we can calculate how bright they actually are. We can also use Class 1a Supernovae as standard candles, because at their maximum luminosity they are of equal brightness. They can be detected at greater distances than 100 million light years. Their redshift can also be used to assess their recession velocity. As to even greater distances, we rely on redshift.

The recently launched James Webb Space Telescope can see much further than the Hubble Telescope, which operates in the optical range. The James Webb operates as an infrared telescope. The more distant galaxies cannot be detected in the optical part of the spectrum, but can be “seen” in the infrared.

The James Webb telescope can detect galaxies and other objects 100 times fainter than those seen by the Hubble ST. It can therefore see much further back in time; much nearer to the time of the Big Bang.

I am sure that Hubble would have been impressed.

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