Prominent northern hemisphere constellations during October include Cassiopeia almost overhead, and Cetus, Pisces, Aries, and Triangulum towards the south, while to the south-west is Andromeda, which is attached to Pegasus, the most conspicuous constellation associated with the northern autumn. Also visible at this time is the Milky Way pouring its incredible number and variety of deep sky wonders across the sky from east to west.
The full Moon occurs on October 5th at 18:40 UTC, and in skylore is referred to as the Hunter’s Moons, which is the first full Moon after the Harvest Moon, or the Moon that occurs closest to the September equinox every year. Note the Octobers’ full Moon rises soon after sunset, and sets just before dawn, which means that the night of the 5th is the only night in the month when the Moon will be visible throughout the night.
Full Moon: 5th
Last Quarter: 12th
New Moon: 19th
First Quarter: 27th
– Mercury is now approaching a position of superior conjunction with the Sun, and will therefore be lost in the Sun’s glare for much of October. Mercury will reappear as an early evening object during the first days of November.
– Venus will be shining at magnitude -3.9 on the first day of October, about 21 degrees above the east-south-eastern horizon, fully two hours before sunrise. On this date, Venus will be about three degrees above and to the right of Mars, which will be shining at magnitude +1.8. Both planets are now moving towards the constellation Virgo, and on the 5th and 6th of the month, Venus will closely pass by Mars at a distance of only about 0.25 degrees to end up close to the waning Moon on the 18th. By month’s end, Venus will be only about 14 degrees or so above the horizon at sunrise, 16 degrees or so below and to the left of Mars, and 5 degrees above Spica, the brightest star in Virgo.
– Mars is having a particularly bad apparition this year, and remains difficult to spot as a result. However, the Red planet rises in the east about two hours before sunrise at the start of October, increasing to about three hours before sunrise by month’s end. At this time, the easiest way to find Mars is to look for it close to the planet Venus, and to track it as it moves into Virgo along with Venus. Mars is now approaching its furthest point from the Sun, which it will reach on October 7, a time when it will be 378 million km (235 million miles) from Earth, making it all but impossible to discern any surface details.
– Jupiter is now approaching the Sun, and although it may still be possible to spot the King of the planets at about 2 degrees or so above the west-south-western horizon during the first few days of October, the planet will be lost in the glare of the Sun for most of October. Jupiter will only reappear as a pre-dawn object around the middle of November.
– Saturn sets about two and a half hours after sunset, reducing to less than two hours after sunset by the month’s end. However, the planet remains low above the horizon during October, and although its angular diameter remains fairly constant at around 16 seconds of arc, and the ring system is now fully tipped towards our line of sight, obtaining good views of the planet remains a challenge due to its low elevation. Nonetheless, look for Saturn about 3 degrees below and to the right of the crescent Moon on the 24th of the month, when the two bodies will be as close to one another as they can be at this time.
– Uranus is now approaching its point of closest approach to Earth, which it will reach on October 19th. As a result, the planet will be 2,830 million km from Earth, and shine at magnitude +5.7, the brightest it will be during 2017. Theoretically, and provided seeing conditions are good, the planet should be visible right through the night on the 19th, so look for it in the constellation Pisces, about 2 degrees from the star Trocularis Septentri (omicron Piscium), which will be shining at magnitude +4.26. However, note that due to its distance from Earth, Uranus may only be visible in large-aperture telescopes.
– Neptune remains visible for much of October, but note that by month’s end, it will around 2 hours after local midnight. Even though Neptune is relatively dim at magnitude +7.86, it culminates in the south at an elevation of about 30 degrees in the middle of October, which should make it easy to find with binoculars about 0.5 degrees below the magnitude +3.74 star Lambda Aquarii. The first-magnitude star directly below the pair (but close to the horizon) will be Fomalhaut (alpha Piscis Austrini).
The month of October sees two meteor showers:
– The Orionids meteor shower runs between October 16th and October 30th, and is expected to peak between the 21st and the 23rd, when about 20 or so meteors per hour should be visible during the pre-dawn hours as the radiant in Orion passes high above the southern horizon. This year, the crescent Moon sets early in the evening, thus providing a dark sky to highlight the debris trail of Comet Halley. Note, though, that Orionid meteors can appear from almost any point in the sky, despite the fact that the actual radiant is in the northern reaches of Orion.
– The Draconids shower emanates from the constellation Draco, and derives from the debris of comet 21P Giacobini-Zinner. However, this minor shower is best viewed during the early evening, but is expected to deliver fewer than 10 or so meteors per hour during the peak that occurs on October 8th. Note also that due to bright moon light on this date, it will only be possible to see the brightest meteors, and then only under dark skies. Note also that like the Orionids, Draconids can appear from almost any point in the sky.
Deep Sky Objects
Below are details on some deep sky objects that can be viewed from urban areas during October:
Messier 52 (NGC 7654)
Located about 5,000 light years away in Cassiopeia, M52 is a magnitude +5 open cluster that presents and easy target for binoculars and small telescopes. This pretty cluster is about 35 million years old, and spans an apparent 13 minutes of arc, which translates into a true diameter of 19 light years. The most luminous stars in the cluster are a pair of yellow giants, shining at magnitudes +7.77 and +8.22 respectively.
Messier 103 (NGC 581)
Also located in Cassiopeia, this small cluster of 172 stars is located about 10,000 light years away, and is an easy target for small to medium telescopes. Although the cluster was discovered by Pierre Méchain in 1781, Charles Messier included it as the last entry in his now-famous catalogue. M103 is relatively young, being only about 25 million years old.
Triangulum Galaxy (M33, NGC 598)
Located in the constellation Triangulum, M33 is the third largest member of the Local Group of Galaxies, after the Milky Way and the Andromeda galaxies. It is also the most distant object that can be observed without optical aid, and host at least 54 large globular clusters, 40 billion stars, and spans around 50,000 light years of space. M33 is linked to the Andromeda Galaxy with a bridge of hydrogen gas, which suggests that the two galaxies have interacted gravitationally in the distant past.