THIS month has a variety of astronomical events to interest everyone. We can look forward to a partial eclipse of the moon, two meteor showers and the chance to see the Andromeda Galaxy, the most distant object visible to the naked eye.
During October evenings the autumn constellations are at their best.
The Plough is to all intents and purposes at its lowest in the north, although it is still reasonably high in the sky.
Cassiopeia is of course now very high and not far from the overhead point. The two bright stars; Vega, which was overhead in summer and is part of the summer triangle, and Capella, which will be overhead in winter, are roughly the same height in the sky. Vega is in the north west whilst Capella is in the north east.
Ophiuchus is now becoming low in the west and is replaced by another faint group, Cetus, the Whale or Sea Monster. Perseus and Taurus, two splendid looking winter groups, are becoming far more conspicuous. The summer triangle of Altair, Deneb and Vega is still easy to see, as is the Milky Way which is directly overhead. The southern skies are now dominated by Pegasus.
On maps the square of Pegasus looks easy to find, but because the four stars are not the brightest in the sky they don’t stand out. However, once recognised it will be easy to find again. One way of finding Pegasus is to look below the ‘W’ of Cassiopeia.
The brightest star in the square is Alpheratz in the top left position. For some unknown reason this star was transferred to the neighbouring constellation of Andromeda. Alpheratz is nearly the same brightness as the North Star, while the other three stars of the square are a little bit fainter.
In mythology, Pegasus was the flying horse ridden by the hero Perseus who, after killing the Medusa, returned to rescue the princess Andromeda who was chained to a rock waiting to be eaten by the Kraken or sea monster. Perseus still had the head of the Medusa with him, so he turned it towards the monster, turning it to stone. All these characters can be found in the sky, including the sea monster.
Andromeda’s main stars are arranged in a somewhat irregular line, running from the Square of Pegasus towards Perseus. However, the main interest in Andromeda is the Andromeda Galaxy, which is visible to the naked eye if you are away from city or town lights.
To find the galaxy, locate the star Beta Andromeda and follow the line of stars; Alpha (or Alpheratz) is the top left hand star in the square of Pegasus; next comes Delta, then Beta Andromeda. Looking upwards you will see the two fainter stars Mu and Nu, and the Andromeda Galaxy is just to the right hand side of Nu. The Andromeda Galaxy is the most distant you can see with the naked eye. It is about 2.5 million light years away.
Below the line of stars that forms Andromeda is a fairly bright star called Hamal, which is the brightest star in the constellation of Aries the Ram. There should be no problem finding Hamal as it is quite isolated. In mythology, Aries represents the ram whose golden fleece was sought by Jason and the Argonauts.
Aries used to be the first sign of the Zodiac. Around 2,000 years ago, the point where the Sun passes the celestial equator from south to north in the sky was in Aries. This point is called the ‘vernal equinox’. However, because the Earth wobbles very slightly over a very long period of time, this point in space has moved into the neighbouring constellation of Pisces, the Fishes. Astronomers still call this place in Pisces ‘The First Point of Aries’.
Between Aries and Andromeda is a small but quite noticeable group of three stars. This is Triangulum, the Triangle, and it is one of the few constellations whose name describes what it actually looks like.
The area below the square of Pegasus is fairly barren. Faint constellations such as Aquarius, Capricornus and Pisces are visible, but Fomalhaut in the otherwise unremarkable constellation of Piscis Austrinus (The Southern Fish) is a good bright star. Use the two right hand stars of the square and draw a line down towards the horizon. Fomalhaut is the brightest star you can see.
Another of the large but faint groups in the autumn is Cetus the Whale. In mythology, Cetus was identified with the Kraken but more recently it has become a harmless whale.
It is a difficult area to identify but there is one star in Cetus that is worth looking out for. It is the normally faint star Omicron Cetus. The star is better known by its proper name of ‘Mira the Wonderful Star’, and it varies in brightness every 331 days, sometimes becoming so bright that it totally transforms the area. Mira is a red giant star and when it brightens it is very noticeably red in colour. It will remain at its brightest for many weeks. Sometimes when at its faintest it is hard to see, and a telescope will be needed to find it.
The Planets in October: It has taken a while but the two big gas giants Jupiter and Saturn are now easily visible in the evening sky. They will in fact be easy to see for next few weeks. If you look to the south you will see a bright white dot in the sky. This is the planet Jupiter. Some distance to the right you can see the planet Saturn which is fainter than Jupiter and looks like a dirty yellow dot in the sky.
If you are up in the morning before the Sun rises you can see Venus, which is often called the Morning or the Evening Star depending on its location in the sky. Apart from the Sun and Moon, Venus is the brightest object in the night sky and it will be seen as a very bright white dot in the south east. The other two naked eye planets Mercury and Mars are both too close to the Sun to be seen this month.
Meteor Showers: There are two meteor showers visible this, month, one very reliable and the other less so. The Orionids so named because the meteors all appear to come from the constellation of Orion the Hunter. The meteors, or shooting stars, are the trail of dust left behind by the famous comet Halley. The peak will be on the night of October 21 / 22 when around 20 meteors per hour might be seen.
The second meteor shower is the Draconids which will peak on the night of October 8/9. They appear to come from the constellation of Draco the Dragon. Harry Potter fans will recognise the name given to the character Draco Malfoy. The Draconids are associated with the comet Giacobini-Zinner. This meteor shower usually only produces a few meteors per hour, but there have been outburst of meteor activity in 1926, 1933,1946,1952,1988 and 2011 so it is always worthwhile having a look to see if there are any Draconid meteors around.
Phases of the Moon for October: Last Quarter 6, New Moon 14, Last Quarter 22, Full Moon 28 There will be a partial eclipse of the Moon on October 28. The eclipse occurs between 8.35pm and 9.53 pm with maximum occurring at 9.14 pm.
An eclipse of the Moon occurs when the Moon passes into the shadow of the Earth. We see the Moon because it reflects light from the Sun. Moonlight is in fact reflected sunlight. During an eclipse of the Moon some light from the Sun passes through the atmosphere of the Earth and is bent or refracted onto the surface of the Moon. The Earth’s atmosphere blocks the blue end of the spectrum, only allowing the red part to get through. This is why, during an eclipse, the Moon turns a coppery red colour. As this month's eclipse is partial, with only the southerly part of the Moon entering the Earth’s shadow, only the bottom part of the Moon will appear to change colour.
The full moon in October is known as the Hunter’s Moon. Following on from the Harvest Moon, this was the month when people would stock their larders with meat for the coming winter. The extra light from the moon this month helped them to locate their prey.
On October 29 British Summer Time ends