Astronomy For Beginners
with the Newbury Astronomical Society
Click on the image to enlarge, ‘right click’ to copy the image or ‘click back or close window’ to return here
One of the Constellations of this Month is one of the best known of all the constellations and is certainly one of the most recognisable. It is Ursa Major (the Great Bear) also known as the ‘Plough’ or ‘the Big Dipper’ in the USA. It has very little resemblance to a bear and looks much more like a ‘Saucepan’ and appears larger in the sky than might be expected.
Ursa Major is almost overhead at this time of the year as can be seen by the chart above. The point in the sky directly overhead of the observer is called the ‘ZENITH’ and is shown in red on the chart. The chart shows the sky as it will appear at 22:00 on 15th July.
Ursa Major is a circumpolar constellation, this means it never disappears below the horizon from the UK and so is always visible somewhere in the night sky throughout the year. All the stars in the night sky appear to rotate around a point in the sky that we call the ‘North Celestial Pole’. This point is located very close to the star Polaris in the constellation of Ursa Minor (the Little Bear).
The sky rotates around Polaris once a year due to Earth’s orbit around the sky. Polaris can always be found by finding Ursa Major. Then by following the two stars opposite the handle of the ‘saucepan shape’, up out of the pan and looking about five times the distance between the two pointer stars that are called Dubhe and Merak in Ursa Major.
Our planet Earth rotates around the North Celestial Pole once a day (24 hours). As Earth rotates the sky appears to rotate above us. As the sky appears to rotate, Ursa Major and the other constellations will appear to move around the North Celestial Pole in an east to west direction. It will appear to move anticlockwise around Polaris as shown on the chart above (handle behind). The movement is slow and not perceivable in real time.
The summer sky is dominated by the ‘Summer Triangle’ first identified by Sir Patrick Moore. The corners of the triangle are marked by the stars Deneb in Cygnus, Vega in Lyra and Altair in Aquila. Albirio in Cygnus can be seen as a beautiful double star when viewed through a telescope. One star is bright and gold in colour the other is fainter and distinctly blue. This is not a true pair they just happen to be in the same line of sight. Although the blue star is much bigger and brighter than the golden coloured star it is a lot further away from us.
The constellation of Lyra (the Harp) is located to the west (right) of Cygnus but is much smaller. The most obvious feature of Lyra is the very bright star Vega that is located the top right corner of the Summer Triangle. Vega is the fifth brightest star in our sky with a magnitude of +0.4. It is located at a distance of 25.3 light years from us and is thought to be 3.2 times the diameter of our Sun and 58 times brighter. The main asterism (shape) of Lyra is composed of a line of three stars with Vega in the centre and a group of four fainter stars that form a parallelogram shape that is known as the ‘Lozenge’.
Between the two lower stars: Sulafat and Sheliak is the Messier object M57. This is a ‘Planetary Nebula’ which has nothing to do with a planet. It is in fact a dying star that was similar to our Sun but older. The star had used most of its Hydrogen fuel and expanded to form into a Red Giant. After passing though that red giant phase it gently collapsed to become a White Dwarf. The very thin outer mantle of the red giant drifted away into space as the star collapsed. The white dwarf is now surrounded by a bubble of gas and dust. It looks like a small ‘smoke ring’ when seen through a telescope but can’t be seen using binoculars. What we are seeing in M57 is what the last gasps of our Sun will be at the end of its existence as a normal star in about five billion years time.
Planets observable: Jupiter, Saturn, (Mars and Neptune early morning).
Follow this link to see the full ‘Monthly What’s Up’ guide to the night sky:
To see a full version of this article and a guide to the night sky with charts, read the Newbury Astronomical Society (NAS) – Monthly Magazines for Beginners are available on the Beginners website at: www.naasbeginners.co.uk.
All meetings of the Newbury Astronomical Society have been cancelled due to the Coronavirus. However virtual meetings will continue on-line using Zoom.