During the summer in doesn't get dark in Northumberland; just a lingering twilight after the Sun goes down. This week astronomical darkness has returned and I've started observing and imaging again.
Last night I too this picture of a little twinkly orange star in the constellation Scutum (the Shield).
The star at the centre of the picture is called UY Scuti. It is very dim - a telescope is needed to pick it out of the thousands of Milky Way stars in the same field of view.
However this is no normal star. UY Scuti is a candidate for being the largest star in the entire Galaxy. Astronomers believe the actual size of UY Scuti is as shown in the picture on the right: big enough to hold 5 billion Suns!
The distance from here to UY Scuti is thought to be around 9,500 light-years and we're viewing it through the gas and dust of the Milky Way's spiral arms and that's why it seems to shine so feebly in the night sky. Appearances are often deceptive in astronomy and UY Scuti is actually about 340,000 times more luminous than the Sun. If UY Scuti were to replace the Sun at the centre of the solar system then the Earth would be inside the star. Along with Mars and Jupiter.
Despite all of this UY Scuti is not that massive - only 7-10 times the mass of the Sun. The density of the star is very low and surface gravity at the boundaries of the star are low too. Red supergiants lose material to the wider universe in solar winds a million times more powerful than the Sun produces. At the end of their lives, they all end with a bang as a type II supernova. At our present distance this would make UY Scuti visible to the naked as it temporarily becomes brighter than even Venus can be in our sky.
Dr Adrian Jannetta
Guitar strummin' explorer of the universe. Mild mannered maths teacher by day and astronomer by night.