A star to measure the size of the Universe!

On Friday last week we hosted the first of our Urban Astronomy sessions in Stoke Bishop. Our theme was one of royalty as we explored the part of the night sky dominated by Cepheus the King, Cassiopeia the Queen and Andromeda, their daughter, unceremoniously chained to rock.

There is some amazing stuff to be seen in this part of the sky - kappa Cassiopeiae, at 4700 light years away, is probably the most distant star visible with the unaided eye. We had on hand a Neolithic axe, if anybody from a star orbiting this star were watching us right now, they would be seeing us in our Neolithic, making amazing stone axes and changing the landscape for ever through the new fangled idea of agriculture!

Delta Cephei, pictured above (from Stoke Bishop) has an awesome history. In 1784 John Goodriche noticed that it changes in brightness - a variable star. In 1912 Henrietta Swan Leavitt discovered that this variability was related to its luminosity. If you could measure the absolute brightness of the star, you could work out how far away it was. A few years later Edwin Hubble found one of these stars in another galaxy - all of a sudden, the Universe was a very big place indeed.

Delta Cephei is a double star, its companion close by, above right in our photo. Anybody living on a planet there would enjoy two sunrises and sunsets sunsets each day.

Our practical observing was rather scuppered by cloud, but with images, artefacts and discussion, we enjoyed a lovely evening of astronomy, history and archaeology.

Our next session will be on 23rd November when we shall be exploring bears and dragons around the north celestial pole, a journey that will take us back to Bronze Age China.

Details are on our website:


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