Astronomy For Beginners
with the Newbury Astronomical Society
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The chart above shows the sky as it will appear at midnight on 15th August to show the positions of all the outer planets. Across the lower part of the chart is the brown curved line depicting the Ecliptic also called the Zodiac. This is the imaginary line along which the Sun, Moon and planets appear to move across the night sky. It is actually the equator of the Solar System and the plane of the orbits of the planets including Earth. The Ecliptic is low at this time of the year due to Earth’s 23.4º tilted axis of rotation. So we see the Moon and planets low in the night sky and the Sun high in the midsummer sky during the day.
All the Superior Planets (outside the orbit of Earth) are visible this month. Venus will be visible in the east before sunrise.
Constellations through which the ecliptic passes this month are: Virgo (the Virgin), Libra (the Scales), Scorpius (the Scorpion). These constellations will have set over the western horizon by midnight. The following constellations can be seen during the night: Sagittarius (Archer), Capricornus (the Goat), Pisces (the Fishes) and Aries (the Ram).
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) which is partly visible at the top of the chart.
Polaris can always be found by first finding Ursa Major and following the two ‘pointer’ stars opposite the handle of the ‘saucepan shape’, up out of the pan. This line points to Polaris about five times the distance between the two pointer stars in Ursa Major.
Our planet Earth rotates around the North Celestial Pole (Polaris) once every 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. The whole sky will appear to move anticlockwise around Polaris. The movement is slow and not perceivable in real time. The whole sky also appears to move east to west by approximately 1º per day due to Earth’s orbit around the Sun every 365.25 days.
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 also known as the Ring Nebula. 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, Neptune, Mars, Uranus (in the evening) and Venus (in the 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. Please go to the NAS website to find how to join our Zoom meetings.