Astronomical Concepts – Week 8 (Final)

For this final week of the course the focus was cosmology.


The main topics of learning we looked at included:

  • Galaxies
  • Quasars
  • Dark matter
  • Dark energy
  • The Big Bang Theory
  • Gravity
  • Expansion of the universe and inflation


There are three main types of galaxy: spiral, elliptical and irregular. Our Milky Way galaxy is a spiral type and contains billions of stars. It is about 100,000 light years in diameter and our solar system is located in the suburbs of the galaxy. At the centre of our galaxy, and also at the centre of most is a super massive black hole. Our nearest galaxy is called Andromeda and we are on a collision course with this galaxy and we will collide in about 4 billion years. Even though the universe is expanding, space is literally stretching like the surface of a balloon being blown up, our galaxies are locked in a gravitational embrace.

Our galaxy is within a local group of galaxies that also contains Andromeda. This local group was first recognized by Edwin Hubble. Even though our local group is a closely packed group of galaxies the distances between the galaxies is enormous. If we travelled at 17.3 km/s it would take us 40 billion years to get to the nearest galaxy (Andromeda). If we could travel at light speed it would only take us 2.3 million years, but this is not possible… yet!


Paul showed some stunning images during the evening and some are shown below.

The pinkish image is of the large magellanic cloud. It is nearly 200,000 light years from Earth and is a satellite galaxy of the Milky Way. It is a highly active star forming vast cloud of gas. Gas slowly collapses to form new stars which light up the gas around them.


This theory proposes a period of very fast expansion of the early universe. It offers solutions to some of the problems of the big bang theory. Inflation is said to have increased the size of the universe by a factor of 10^26 in only a fraction of a second. But, it also has problems! Here is why thanks to New Scientist.

Screen Shot 2016-12-02 at 12.28.54 am.png

The cosmic microwave background was another featured topic tonight and here it is.IMG_2857

This image shows the universe in microwaves. It shows the temperature fluctuations of the early, early universe, about ~300,000 years after the big bang. The image is a record of a time when the early universe cooled to around 3,000 Celsius and protons and electrons were able to form atoms. As a result photons were able to escape and travel freely around the universe. The CMB was discovered in 1965 by Penzias and Wilson and they hared the Nobel prize in physics for this discovery in 1978. Today the CMB is very cold, just 2.725 degrees above absolute zero which means the radiation shines in the microwave part of the electromagnetic spectrum and is invisible to the naked eye. However, we know it is there, everywhere in the sky and if we could see it ourselves we would see the entire sky glow with a very uniform brightness in every direction. The temperature is uniform to better than 1 part in a thousand. This is the main reason to why scientists think it is the remnants from the big bang, because what other event could have been the cause. By studying the CMB further we can learn about the conditions of the early universe in great detail.

Dark matter and dark energy

These theories are still a mystery. We know a lot about our universe and one thing we know is that about 0.4% of the mass of the universe is made of stars, dark matter is about 27%, dark energy is about 68% and the remainder is gas, mainly hydrogen. Here, again thanks to New Scientist are dark matter and dark energy explained in more detail.


There, described beautifully, thank you New Scientist!

Limitations of the big bang theory


The fate of the universe! There are two theories: endless expansion and the big crunch. If the universe continues to expand forever then it will also continue to cool down until it is unable to to sustain life. On the other hand, if gravity wins and takes back control over expansion and there is sufficient mass to be able to do this then the universe will start to collapse back in on itself – the big crunch! Recent evidence suggests the universe is still expanding and at an increasing rate. This could be the dark energy mentioned earlier.

Paul left us where we started 8 weeks ago with the Hubble Deep Field image.


This is an image of a tiny patch of the night sky that was believed to be blank, empty space. The Hubble Telescope focused on this tiny patch of sky and took a long exposure image over 10 days, and this was the result. The image shows over 300 galaxies, everything in the image is a galaxy and some of the farthest and oldest ever seen. The image is very important to scientists and researchers to see how the universe has developed and changed over time. it is one of the most important images ever taken!

This was an amazing course packed full of super-interesting information about our universe, solar system, stars, planets and the theories that shape our lives. I recommend it to everyone! Follow the link to sign up for the next instalment.

Massive thanks go to Dr Paul Payne for your amazing lectures, graphics, stories, jokes, cups of tea and biscuits!


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