October Sky Notes
Written by John Stapleton
Image Credit: Sky at Night Magazine
A Month for Unusual Eclipses
October sees the clocks go back an hour to GMT or Universal Time on the 29th of the month. Unlike many people who do not look forward to this time of year of darker, longer nights, for astronomers this is a good thing; there are more hours of darkness, and they begin earlier in the evening so that general observations can be made within a more comfortable timeframe. Of course we still have to wait for specific events if they are to be seen. The darker Autumn sky therefore gives us the chance to pick out the summer sky constellations and objects against a darker background. The increase in contrast that this provides means that objects can be seen more clearly and for longer. The Autumn constellations can also be seen at their best. This year, for most of the night, the four giant planets can be seen against a dark sky at the same time: Uranus, Jupiter, Neptune and Saturn are strung out across the sky from East to South. Of course some of these are brighter and more obvious than others but I hope that the sky notes will help you to locate the others.
This month sees two unusual eclipses. On 14th October an Annular (ring-shaped) Solar Eclipse occurs, unfortunately it will not be visible in the UK. The appearance of a ring of sunlight against the dark shadow of the Moon is caused by the Moon being closer to the Earth than usual, so that it does not quite blot out the entire solar disc. This, of course, happens on the day of New Moon as both Sun and Moon must be in the same part of the sky. Then, on October 28th, the night of Full Moon, there will be a partial Lunar Eclipse. From the South of England only about 12% of the Lunar surface will be in shadow. The greatest extent of the shadow occurs at 20:15 GMT (UT) or 21:15 BST.
In space news, the Indian Lunar Probe, Chandrayaan 3, after successfully landing and deploying its Rover, which was put into sleep mode to help it survive the cold of the Lunar night, has not responded to signals meant to re-activate it to continue its exploratory mission.
Sky Notes
Please note all times given in this article are in GMT so remember to add an hour to get the time in BST.
Sun: From the beginning to the end of the month the period of dark sky increases from 8.5 hours to over 10 hours. The longer nights allow us to view the summer constellations and the Milky Way that runs through them against a dark sky whilst also introducing the Autumn constellations and the interesting objects in them.
Mercury: Mercury is not visible this month as it lies in the same direction as the Sun.
Venus: Venus rises in the East about 3 hours before the Sun and can be seen against the background stars of Leo, below the asterism of the Sickle (looks like a back-to-front question mark). The planet reaches its greatest Western elongation on 23rd.
Mars: Mars is also not visible this month as it rises after the Sun and in the same direction.
Jupiter: The largest planet visible throughout the night and reaches a good elevation by 9:00pm against the background constellation of Aries. The coloured bands and zones on the surface of the planet can be distinguished with small telescopes as can the Great Red Spot, a colossal hurricane, greater in diameter than the planet Earth. The Galilean moons can be seen with a good pair of binoculars or a small (bird-spotting) telescope. DSLR images of the planet will also pick up the moons. These moons orbit Jupiter such that we sometimes see them pass between the Earth and the giant planet along our line of sight. Watch out for small black dots seen against the surface of Jupiter itself. And sometimes we see that the moons have passed behind Jupiter and fewer of them are visible. At the end of the month the Full Moon lies just to the North of Jupiter.
Saturn: The ringed planet can be found against the stars of Aquarius, visible all night long and at a maximum altitude of about 25 degrees (a little more than the span between your thumb and little finger, at arm’s length). The rings are becoming more open, from our point of view and are consequently becoming brighter. Saturn’s largest moon, Titan, can be seen with a good pair of binoculars or a small telescope.
Uranus and Neptune: Uranus is visible all night long throughout October and is seen against the background stars of Aries between the Pleiades star cluster and Jupiter. It is now only a telescope object as it is receding in distance from the Earth. Look for a tiny greenish disc compared to the pinpoints which are the stars. Neptune is seen against the background stars of Pisces (below the asterism known as the Circlet, which represents one of the fish) and about a third of the way back along a line joining Saturn and Jupiter. Neptune will also require a telescope to find it. Neptune displays a smaller and truly blue disc compared to that of Uranus although it will appear only as a bluish star to most small instruments.
Meteor Shower: The Orionid meteor shower can be seen this month, occurring between 15th and 29th with a peak on 21st. These are relatively fast-moving meteors although still only up to 10 an hour. The Moon is nearing First Quarter, so this is a good opportunity to see these meteors. The Orionids are interesting because they are formed from the debris left behind in the wake of Comet Halley.
Comet: There are no bright comets expected this month. However there are two short period comets that are well placed in the sky. The first is Comet 2P/Encke with a period of 3.3 years, one of the shortest known orbital periods of any comet. This comet appears regularly in our skies but is not generally easily visible. This year the comet passes through the prominent constellation of Leo and could be visible to observers with telescopes in the early hours of the morning. The second is Comet 103P/Hartley 2 which has a period of about 6.4 years. This comet is also found in an easily identifiable area of sky as it passes along the length of the box-shape that represents Gemini and heads into Cancer at the end of the month. Comet Hartley is predicted to reach, at least, binocular visibility and the best time to see it will be between 19th and 27th October, when there is no Moon in the sky. Unfortunately, this, again needs to be in the early hours of the morning, before 2am.
The Last Quarter Moon occurs on October 7th with New Moon on 14th, First Quarter then follows on 22nd October and Full Moon on 28th.