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The Sky at Night for October 2016

Events in DARK text happen during darkness. LIGHT text during daylight, i.e. we can't see them.

Note: Times are calculated for Liverpool and will vary slightly across the UK

Planet Date Rises ? Transits ? Sets ?
Planet Event ? Date Time Sun Angle ? Each month, we identify the best constellations to be seen from the UK between 9pm and 10pm.

This month we'll be looking for the autumn constellations of Aquarius, Cepheus, and Pegasus,
which can be found close to an imaginary line running North to South in the October night sky.

Night Sky in October

Aquarius - is named after the Latin word for a 'Water-bearer', and is the 10th largest of the 88 modern constellations. It is also one of the 12 constellations through which the ecliptic passes and is therefore one of the signs of the zodiac. The ecliptic is an imaginary line across the night sky that the planets never stray far from during their orbits of the Sun. It marks out the plane of our Solar System, or alternatively, can be used to indicate the direction of its rotation axis (at right angles). Despite being large, Aquarius only has 2 bright stars, with the brightest being Sadalsuud. One of the more notable objects in the constellation is the recently discovered Gliese 876 planetary system, which is known to have at least 3 planets orbiting a red dwarf star. One of these is a terrestrial planet around 6-8 times the mass of Earth.

Cepheus - is named after Cepheus, King of Aethiopia in Greek mythology, and is considered to represent a king. It is the 27th largest of the 88 modern constellations and can be identified by looking close to Polaris (the North Star) for a box shape with a triangle on top. Many observers think this shape looks somewhat like a royal crown. Cepheus contains just one bright star, called Alderamin, but enjoys a number of other interesting objects, such as the Fireworks Galaxy (NGC6946). NGC6946 is a spiral galaxy in which eight supernovae have been observed, more than in any other galaxy. The constellation is also home to a binary star system, γ Cephei, which is just 50 light years from Earth and marks out the point of the crown shape. Due to the precession of the Earth (its rotation axis changing direction - a bit like a spinning top), this system will become the North pole star between 3000 A.D. and 5200 A.D. - with the closest approach being around 4000 A.D. Cepheus also contains the prototype Cepheid variable star, named δ Cephei, which was discovered in 1784 and found to periodically double in brightness (and then dim again) over the course of 5.4 days. The variation has continued over hundreds of years and is thought to be caused by unstable layers in the outer atmosphere of stars in the latter stages of their lifetime.

Pegasus - is named after the mythological winged horse of the gods, Pegasus. It is the 7th largest of the 88 modern constellations and contains 5 bright stars, the brightest of which is Enif (see above), which is said to represent the nose of the horse. The easiest way to find Pegasus is by looking for four bright stars that make up the shape of a box, known as the Great Square of Pegasus. The four stars of the square are Sirrah (top-left), Scheat (top-right), Algenib (bottom-left) and Markab. The constellation has become more studied in recent years because it is home to the first extra-solar planet ever discovered, which orbits the star 51 Pegasus every 4.2 days (Mercury orbits every 88 days). The word extra-solar means that the planet is outside our own Solar System. Such a short period means that the planet orbits very close to its parent star, which was totally unexpected by astronomers. The planet is now known to be a gas-giant planet, like Jupiter or Saturn, with an atmospheric temperature well over 1000°C. Another planetary system in Pegasus, HD209458, has provided the first evidence that water vapour exists in the atmosphere of a planet outside of our own Solar System.