1. William Herschel(d 1821)
With his sister Caroline made careful maps of the heavens and discovered the planet Uranus. William’s son John continued the work in the Southern skies.
After Newton, bigger and better telescopes were built and people set out to make the best catalogue that they could of what was up there. William with his sister Caroline worked in Bath and later his son John moved to the Canary Islands to get a better look at the southern skies. Light is the only clue we get from the heavens. In this picture you can see William examining the spectrum of light from the sun and in the background you can see the telescopes he used both small and big.

2. Light from a star can be separated into the spectrum of colour seen here. The black lines show where certain wavelengths of light have been removed from the spectrum because the light has passed through cooler gas surrounding the star. The black lines tell us the name of the gas through which the light has passed.
Let the students read this and ask questions.

3. The black lines are called Fraunhofer lines after the man who first described them in the spectra of the sun. He also detected them in the spectra of other stars.
As well as the black lines that you can see in this picture, it was also found that the brightest colour was also an indicator of how hot the light emitter was. So in the graph that you can see above the spectrum, you can see which colour carries the most energy. Out own sun emits most strongly in the yellow, so we know the outer layers of our sun are at about 6000 degrees C.

4. Edwin Hubble
In the 1920s Edwin Hubble used methods developed by Henrietta Livett to measure the distances to the most distant galaxies known then.

5. William Herschel found many cloudy objects as well as stars
William Herschel found many cloudy objects as well as stars. Some had a regular shape and others were irregular. At the start of the 20th Century, it was not known whether these objects were nearby inside our galaxy or whether they were much larger and very much further away. How can you measure the distance to something you cannot reach? (Say this in an exasperated way.) In fact this photo is of a cluster of galaxies. Every blob you can see is in fact an aggregate of billions of stars and the cluster may be 100s of millions of light years away.

6. Henrietta Levitt measured the distance to this spiral Andromeda
Henrietta Levitt measured the distance to this spiral Andromeda. It turned out to be 2.5million light years away. This put it way outside our Milky Way. The rash of stars you can see all over the photo are part of our galaxy. They are in the foreground. The spiral is like our own Milky way, it contains billions of stars just like our galaxy does. The blobs below and above are other galaxies held near Andromeda by the force of gravity.

7. If a source of sound or of light is moving with respect to you, the wavelength will be distorted. If the light source moves towards you, the frequency will seem higher and we say it is blue shifted. If the source moves away the wavelength appears longer and the light is shifted towards the red end of the spectrum…. Red-shifted.

8. This amazing picture is of a galaxy that is spinning
This amazing picture is of a galaxy that is spinning. The colours have been enhanced, but can you tell which way the galaxy is spinning?

9. Hubble measured the distances to many galaxies
Hubble measured the distances to many galaxies. He noticed that the light was always red-shifted. Every distant galaxy was moving away. He graphed the speed of the galaxy against its distance. The more distant ones were going faster. Since the further away you look, the further back in time you are looking, it means that once the universe was moving faster than it is now.

10. If you look at the yellow arrow in the left hand set of pictures you can see that a particular spectral line has shifted further and further to the left. The shift is an indicator that the source of light is moving. The amount of shift tells us how fast it is moving and the fact that the shift is towards the red end of the spectrum tells us that the source is moving away from us. The pictures on the right show by their size how far away the source is. You can see that the further away the galaxy the faster it is moving. Hubble concluded that the universe was expanding. This was the first piece of cosmological data because until this time no-one had detected any kind of motion like this. The universe was thought to be stationary. If this was the case then it has no history! If it moves, it has a beginning and a future. The study of this is called cosmology.

11. All the evidence collected in the last 70 years suggests that the universe began about 13 billion (thousand million ) years ago in an incredibly compressed state. It has been expanding ever since and has co-alesced into clumps that we call galaxies.

12. The Universe seems to be marginally bound. We are at a
If you throw something in the air gravity will pull it back down. If you throw it hard enough it may escape the earth if it has enough energy. One of the hot questions in Cosmology is whether the the Big Bang banged hard enough for the universe to escape itself, (unbound) or whether there is enough mass in the universe to cause it to fall back in on itself. (bound)
Questions you have to ask are “Where did the energy for the first big bang come from?”
“Is gravity the only force in town or is there something else that we don’t know about yet?”
The Universe seems to be marginally bound. We are at a
point where we just can’t tell whether the Universe is going to
Implode, blow apart (blue line), or slow down but never quite stop.

13. It is very hard to imagine reality
It is very hard to imagine reality. We are reduced to drawing 2D pictures in an attempt to understand what is going on in space and time. These always leave us with questions that just won’t go away because the universe is very there.

14. was perfectly even and there would be no uneven pockets of mass to act
When the universe was closely packed early in its history, radiation (ie light) did not travel very far before it interacted with the atoms that were being formed. At one point the universe reached a low enough density for the light to escape. The universe has expanded so much that this original radiation has now stretched and makes it appear that it comes from a body at about 3 degrees above absolute zero. This is called the background radiation. This evidence was collected in 1990.
If the background radiation was even it would show that the early universe
was perfectly even and there would be no uneven pockets of mass to act
as seeds for the galaxies and we would not be here. This picture shows
the background radiation to be uneven, so the Big Bang model is
supported.