Astronomy

Astronomy
Astronomy Guide to the Night Sky – September 2017

With the Newbury Astronomical Society

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The chart above shows the night sky looking south at about 22:00 BST on 15th September.  West is to the right and east to the left.  The point in the sky directly overhead is known as the Zenith or Nadir and is shown at the centre of the chart.  The curved brown line across the sky at the bottom is the Ecliptic or Zodiac.  This is the imaginary line along which the Sun, Moon and planets appear to move across the sky.  The brightest stars often appear to form a group or recognisable pattern; we call these ‘Constellations’.

Constellations through which the ecliptic passes this month are Sagittarius (the Archer), Capricornus (the Goat), Aquarius (the Water Carrier), Piscis (the Fishes), Aries (the Ram) and Taurus (the Bull) is about to rise over the eastern horizon.

Just disappearing over the south western horizon is the constellation of Sagittarius (the Archer).  It is really a southern constellation but we can see the upper part creep along the horizon during the summer.  The central bulge of our galaxy is located in Sagittarius so the richest star fields can be found in the constellation along with many of the beautiful and interesting deep sky objects that we seek out.

The summer constellations are still prominent in the night sky lead by Hercules (the Hunter).  Following Hercules is the Summer Triangle with its three corners marked by the bright stars: Deneb in the constellation of Cygnus, Vega in Lyra, and Altair in Aquila.  The Summer Triangle is very prominent and can be used as the starting point to find our way around the night sky.  See the following pages.  The Milky Way (our Galaxy) flows through the Summer Triangle passing through Cygnus, down to the horizon in Sagittarius.

The Milky Way flows north from the Summer Triangle through the rather indistinct constellation of Lacerta (the Lizard), past the pentagon shape of Cepheus and on through the ‘W’ shape of Cassiopeia (the Queen).

At the top, centre of the chart above is the fairly faint constellation of Ursa Minor (the Little Bear) also called the Little Dipper by the Americans.  Although Ursa Minor may be a little difficult to find in a light polluted sky it is one of the most important constellations.  This is because Polaris (the ‘Pole’ or ‘North Star’) is located in Ursa Minor.  Polaris is the star that is located at the approximate point in the sky where an imaginary line projected from Earth’s North Pole would point to.  As the Earth rotates on its axis, the sky appears to rotate around Polaris once every 24 hours.  This means Polaris is the only bright star that appears to remain stationary in the sky.

At the top right of the chart (North West) is the constellation of Ursa Major (the Great Bear).  The saucepan shape of the constellation is often called the Plough in the UK but is also known as the Big Dipper in the USA.  It does actually look remarkably like a saucepan.  Four bright stars represent the pan and three stars represent the handle.  An imaginary line drawn from the side of the ‘pan’ opposite the handle points to Polaris (the Pole Star).  See the chart above.

To the East of the Summer Triangle is the constellation of Pegasus (the Winged Horse).  The main feature of Pegasus is the square formed by the four brightest stars.  This asterism (shape) is known as the Great Square of Pegasus.  The square is larger than might be expected but once found is easier to find again.

Follow this link to see the full ‘Monthly What’s Up’ guide to the night sky:

http://naasbeginners.co.uk/Whats_up/2017_2018/September2017.htm

To see a full version of this article and a guide to the night sky with charts, read the Newbury Astronomical Society (NAS) – Monthly Magazine for Beginners on the NAS website or come along to the next Beginners meeting on 20th September 2017.

For details visit the NAS website at: www.naasbeginners.co.uk

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