Sky notes for 2023 October & November

2023 October 1

Nick Hewitt

Oct 29 sees the end of British Summer Time and we are deep into autumn. Nevertheless, the northern summer stars remain prominent, with Cygnus flying high from early October until Christmas.

The best guide to the autumnal constellations is Pegasus, the flying horse. The large Square of Pegasus is not a brilliant asterism, but once located is most useful and sits on the meridian at 21:00 UT at the beginning of November. The western stars of the Square are both magnitude 2.4, alpha (Markab) the lower, beta (Scheat) the upper; the eastern stars are gamma (Algenib) and delta (Alpheratz), the latter being the brightest of the Square at magnitude 2.0. It is shared by Andromeda as alpha Andromedae.

From the Square, it is straightforward to find Pisces to the south and east, Andromeda streaming from the north-east corner, Aquarius to the south-west, and the regal pairing of Cepheus and Cassiopeia to the north. Epsilon Pegasi (Enif) supervises summer giving way to autumn, and nearby is the superb globular cluster Messier 15. Slightly to the west of Enif lies a waste of space in the form of Equuleus, the foal. Why Hipparchus felt the need to add this little horse is a mystery! Represented on most atlases as just a head, it possibly represents Celeris, the brother of Pegasus, but has unpleasant shades of a scene from The Godfather film. Other names include Kitalpha, although this more commonly refers to its undistinguished alpha star. It is the second smallest constellation and contains nothing of interest other than the doubles delta and epsilon Equulei.

Delta is a very tight binary of magnitude 4.49, with a separation never exceeding 0.35 arcseconds, so is a real test for larger apertures. However, it is known for having one of the shortest periods of any visual binary pair: just 5.7 years. Another close binary is epsilon Equulei, a 5th-magnitude system currently at periastron and only 0.1 arcseconds, so wait a while until an apastron of 1.1 arcseconds. Lambda poses yet another close test, its evenly matched stars both being magnitude 7.4, but at a manageable 2.8-arcsecond separation. There are also a few unexceptional galaxies in the constellation.

In late October, Lacerta the lizard scuttles to the west of the meridian while magnificent Cassiopeia regally lies to its east. Lacerta is faint – a narrow zig-zag of 4th- and 5th-magnitude stars nestled between eastern Cygnus and western Andromeda – but by skulking on the edge of the Milky Way, it contains several attractive open clusters in a rich star field. NGC 7209 is one of the best: a large, irregular array of 10th-magnitude stars on the western border with Cygnus. Others include IC 1442 and NGC 7245, which lie close together in the north of the constellation and form a target for wide-field imaging. IC 1434 is a faint, rich tick shape just to their south-west.

Lacerta boasts an extraordinary Active Galaxy that can be followed by amateurs. BL Lac was thought to be a highly irregular variable star when discovered in 1929, but in 1968 it was found to be a bright variable radio source. Then the faint host galaxy was picked up and its true nature realised. Now the prototype of its class, BL Lac objects are ‘blazars,’ a class of active galactic nuclei (AGN). It sits in a rich star field on the western aspect of Lacerta and is quite tricky to identify, especially at minimum (around 15th magnitude).

In contrast to Lacerta, Cassiopeia is one of the grandest and most familiar of the northern constellations, with its characteristic W shape (in autumn). There is so much within, it is hard to know where to start. Sweep the northern Milky Way with binoculars, and you will find it chock-a-block with plums for telescopic observers. Lying near the zenith at the end of October, the numerous open clusters alone can occupy several evening sessions. Sweeping from west to east, some of the best open clusters in the sky can be easily found. Messier 52, NGC 7789, NGC 457 and Messier 103 are all superb and varied in appearance.

NGC 7789 is nicknamed Caroline’s Cluster as it was discovered by Caroline Herschel, sister to William. It is wonderfully rich and easily found, a little south of beta Cassiopeiae (Caph) at the end of the ‘W’. More tricky targets include the emission nebula NGC 281 (the Pacman Nebula) and the faint nebulae near gamma Cassiopeiae, IC 59 and 63. IC 63 (‘the Ghost’) is an emission nebula energised by nearby gamma Cassiopeiae, while IC 59 reflects the light of Cassiopeia’s central star. Imagers enjoy tackling the huge diffuse emission-nebula complex to the south-east of epsilon Cassiopeiae, nicknamed the ‘Heart and Soul’ nebulae (IC 1805 and 1848); these respond spectacularly to narrowband imaging.

Nestled below Andromeda, east of Pisces and north of Aries sits Triangulum; its shape is in the name. It has one major object of interest: the Local Group galaxy Messier 33. This is on the western edge of the small constellation, an easy sweep north-west from alpha Trianguli. The galaxy, a face-on spiral, is magnitude 5.7 but this is spread over 67×42 arcminutes, an area greater than the full Moon, rendering it low surface-brightness. While technically visible to the naked eye from the darkest of sites, it is rarely seen without aid. Normally fairly easily picked up in binoculars, its large size can make it elusive in telescopes if not wide-field. Persistence is rewarded once found, as numerous knots can be found in the spiral arms, several having separate NGC numbers. The best is NGC 604, an enormous emission nebula 40 times the size of our Orion Nebula. If placed at Messier 42’s distance from us, it would outshine Venus and cast shadows!

The solar system

Hopefully the Sun will remain active and well observed despite its diminishing altitude. There is an annular eclipse visible on Oct 14 but only from the USA, Central America, and Brazil. Nothing of it can be seen from the UK.

On Oct 28, a partial lunar eclipse is visible from the UK. Only a small part of the southern aspect of the Moon enters the umbra, although the whole Moon falls into the penumbra. First contact with the penumbra occurs at around 18:00 UT (geography-dependent), and the umbral phase is between 19:35 and 20:52 UT so if clear, it is at a comfortable time of evening.

Mercury is just visible before dawn early in October, ending its fine morning display, but it then heads towards superior conjunction on Oct 20. It is too difficult to view throughout November evenings.

Venus is at greatest western elongation on Oct 23, but remains brilliant throughout November. There is a daylight occultation by the waning crescent Moon on Nov 9. This will be at a safe distance from the Sun and the pair will provide a stunning sight before dawn, which will be a good time to set up. It should then be easy to follow them into daylight and enjoy Venus disappearing on the bright side of the Moon around 09:45 UT, reappearing from the dark side at around 10:48 UT. Exact times depend on your geography.

Mars is unobservable, being at conjunction with the Sun on Nov 18.

Jupiter dominates the autumn evenings and is at opposition on Nov 3, so is observable all night. It is magnitude –2.8 in Aries, so no star competes.

Saturn is well placed for early evening observation, slowly moving through Aquarius. The rings are quite obviously closing up, although the ring-plane crossing is not until 2025. Identifying the brighter moons is fun, with Tethys, Dione and Rhea being around 10th magnitude, and Titan an easy 8th magnitude. Try for Mimas at magnitude 13, or Iapetus – not that faint (11th magnitude) but often distant from Saturn so tricky to identify.

Uranus is in eastern Aries and well positioned at opposition on Nov 13. Its small greenish disc (3.7 arcseconds) should differentiate it from the nearby stars.

Neptune is past its September opposition in Pisces, but gives a good evening opportunity for location and observation with large-aperture telescopes. Within a rhomboid pattern of stars of around 6th to 7th magnitude, its somewhat fainter bluish disc (2.4 arcseconds) should identify it well enough. Spot Triton orbiting Neptune around every six days, in its unusual retrograde path.

Meteors

This is a very good season for meteor enthusiasts, all the showers of October and November being favourable.

The Draconids may be worth watching on the evening of Oct 8, as the Moon will not interfere. The shower derives from comet 21P/Giacobini–Zinner and is generally weak, but occasionally puts on a good display. The radiant is in the head of the dragon, so is high up in the north-west by mid-evening.

The Southern and Northern Taurids have a splendidly favourable showing in 2023. The Southern Taurid maximum is on Nov 5 when the Moon is at last quarter; the Northern Taurids peak a week later, when the Moon is new. Both of these showers have wide ranges of activity between mid-September and early December, the Southern stream being swift, often with persistent trains, the Northern being slower. They are therefore easily distinguishable, although both radiant points are near the Hyades star cluster.

The Orionids will not be compromised by the Moon when they peak on the night of Oct 21–22, although their maximum is broad. These speedy meteors derive from comet 1P/Halley.

It is now 24 years since the famous Leonid display of 1999 November, and we must wait a further nine before the next potential storm in the 33-year cycle. The shower peaks on Nov 18 and the Moon sets in the early evening, so what meteors there are should be readily seen. The shower is derived from comet 55P/Tempel–Tuttle.

Comets

Perhaps the most interesting comet this autumn is 103P/Hartley: one that the Comet Section is eager to monitor. However, it is not bright! It was discovered in 1986 and was visited by the EPOXI spacecraft in 2010, showing us that its 2km nucleus is peanut shaped. One of the Jupiter family of comets, with an orbit of 6.5 years, it passes through Gemini in October and is at perihelion on Oct 12. See more at: bit.ly/3EMlNFa.