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Sky Diary

The Sky at Night

Cygnus, the Swan, is high in the south by 10pm and the nose of Pegasus is just on the meridian. This is the time of year when the fine autumn constellations are high in the sky and the cross of Cygnus and the square forming the body of Pegasus are easily identified. The Square of Pegasus is a bit to the east of due south and the hind leg of the inverted horse blends into the constellation of Andromeda. I always have the feeling that seeing these two constellations high in the sky heralds the entrance of the glorious winter constellations. Below these constellations are the much less prominent shapes of Aquarius and, near the southern horizon, Capricornus. Neither of these constellations have any bright stars and light pollution often makes them completely invisible although they can be identified from darker sites.

On a clear moonless night it is worth making a trip with binoculars along the constellation of Cygnus beginning above its brightest star, Deneb. Not far above Deneb you will see a cluster of stars which is known as Messier 39. This is an open star cluster around 1,000 light years distant, discovered in 1749, and an ideal subject for binoculars. Move towards and slightly east of Deneb and you may just see a small fuzzy patch of light. This is the North America Nebula, a cloud of interstellar gas and dust which has the shape of the country it is named after when seen on photographs. Following the line of stars which represent the body of the swan, just to the east of the central star is another open star cluster, this one designated Messier 29 and around 6,000 light years away. Continue downwards to the star which marks the head of the Swan, sometimes known as the 'beak star' and you will find a beautiful double star, one being bright yellow and the other a sapphire blue. Finally, below this star, Albireo, and moving into the constellation of Vulpecula, you will find a small group of stars which look remarkably like an inverted coat hanger and is indeed known as 'the Coathanger'. With the exception of the North America Nebula, all these objects are easily visible with a pair of average binoculars.

The autumnal equinox this year falls on September 23rd at 8am. This is the time when the Sun crosses the equator and begins its southerly journey. Sunrise at Dundee on that day is 6.58 am and sunset 7.09 pm so the Sun is above and below the horizon for about 12 hours. Because of latitude, this is not exactly 12 hours each and equal day and night at this latitude usually occurs on September 25th.

The Planets

Mercury

Mercury

Mercury and Venus are in the vicinity of the Sun in the early part of September but both move westwards later in the month. However, they set at around the same time as the Sun and will not be visible.

Venus

Venus

Venus and Mercury are in the vicinity of the Sun in the early part of September but both move westwards later in the month. However, they set at around the same time as the Sun and will not be visible.

Mars

Mars

Mars moves eastwards from the Sun during the month but will not be far enough away from it by the end of the month to be seen in the morning sky before sunrise.

Jupiter

Jupiter

Jupiter will remain bright but low in the south south-west following sunset and will set in the south-west at 10pm.

Saturn

Saturn

Saturn follows Jupiter in the southern sky and will be almost due south at 9pm. It will appear like a bright star but considerably less bright than Jupiter.

The Moon

The Moon

The Moon will be at first quarter on the 6th, full on the 14th, last quarter on the 22nd and new on the 28th September.