The Night Sky This Month: October 2019

Pegasus Constellation and M31
Credits: Image courtesy of Stellarium

October’s night sky presents the opportunity to see the Summer Triangle in the southern sky in the early evening. Meanwhile, to the east of Cygnus is another famous asterism, namely the Great Square of Pegasus. The huge square is formed from the stars Markab, Scheat and Algenib, and also Alpheratz, which lies in the neighboring constellation of Andromeda, where the Andromeda Galaxy (M31) is found. In the early morning, the Pleiades and Orion then start making an appearance.

The Moon

Lunar observers have two excellent opportunities to test their observing skills during October. Favorable illumination on the night of the 6th and again on the 19th will highlight the Hyginus Rille, a supposed collapsed lava tube that cuts through the Hyginus Crater.

Unlike impact craters that usually have raised rims and central peaks, the Hyginus crater is simply a hole in the lunar surface that is thought by many planetary scientists to have been created when a lava pocket either drained or exploded, which caused the overlying material to collapse into the empty space. While the crater is relatively easy to spot, seeing the rille is often a lot more difficult, so see if you can find it on the dates stated.

Moon Phases

New Moon First Quarter Full Moon Third Quarter
October 28th October 6th October 14th October 22nd

Planets in October 2019

Planetary viewing conditions improve somewhat during October. While there is still not much to get overly excited about, at least one planet starts a new apparition toward the end of the month. Below are some details of what to expect from the planets:

Mercury is now approaching its position of greatest elongation from the Sun, which it will reach on the 19th. That’s when it will be 24.6 degrees east of the Sun. Note that because the ecliptic has a very shallow angle with respect to the equator at this time, Mercury will not rise more than about 1.5 degrees above the south-western horizon. This will make it very difficult, if not impossible to spot the little planet just to the upper left of Venus.

Venus will set about 30 minutes or so after the Sun as October begins. Even though it will be relatively bright at a magnitude of -3.9, the shallow angle of the ecliptic with respect to the equator will make it extremely hard to spot the planet. By month’s end, Venus will set about one hour after sunset. The disc will be fully illuminated at this time, but its very low elevation will still make it very difficult to see in the south-west.

Mars passed behind the Sun on the 2nd of September, and will reappear as a pre-dawn object in the second half of October. Although it will shine at magnitude +1.8 in the southeast when it does reappear, it will be only about 11 degrees above the horizon. Binoculars could well be needed to spot the Red planet, but be mindful of the fact that binoculars should not be used after the Sun has risen.

Jupiter starts October shining at magnitude -2.0, but it dims to magnitude -1.9 as the month wears on. Jupiter is still sinking towards the southern ecliptic, so it will not rise more than about 10 degrees or so above the southern horizon. This will greatly hinder attempts to get clear views of the King of the planets. However, an atmospheric dispersion corrector could be of some help.

Saturn will, like Jupiter, not rise more than 10-14 degrees above the southern horizon during October. Even though it will be relatively bright at magnitude +0.5 to +0.6, its low elevation will make it difficult to get clear views of the ring system, which now spans across 41 seconds of arc.

– Uranus is now approaching a point of opposition, which it will reach on the 28th of the month. As a result, the planet will be visible for most of the night and it should therefore be relatively easy to spot the planet with binoculars or even with the naked eye if the sky is sufficiently dark. Medium-sized telescopes will resolve the planet’s turquoise color, so look for it in the constellation Aries, close the Pisces/Cetus border.

October’s Meteor Showers

October sees two meteor showers, including the Orionids, which is one of the 10 best meteor showers of the year. Meanwhile, the annual Draconids kick’s off this month’s celestial light show.

The Draconids Meteor Shower peaks early on the evening of the 8th of the month. This shower is classified as weak, and it rarely produces more than about 10 or so meteors per hour during its peak. However, the first quarter Moon sets soon after midnight, so at least the brightest meteors might be observed from dark skies. Although the shower’s radiant is in the constellation Draco, meteors can arrive from any point in the sky.

The Orionids Meteor Shower results from debris left by Halley’s Comet, and it peaks on the night of the 21st/22nd. Up to 20 or so meteors per hour is expected during the peak this year. Since the second quarter Moon’s light will block out some of the fainter meteors, though, considerably fewer than 20 meteors per hour might be visible. This shower’s radiant is in the constellation Orion, but meteors can arrive from any point in the sky.

Deep Sky Objects: October 2019

Constellations that are prominent in the sky at this time of the year include Lyra, Cygnus, Perseus, Aquila, Andromeda, Pegasus, and Cassiopeia. These contains several pretty star clusters that are visible with large binoculars and telescopes with medium-sized apertures. Below are some details of these star clusters, with all these deep-sky objects observable from urban skies in the constellation of Cassiopeia. See if you can find them during the month.

Messier 52 (NGC 7654)

Credit: 2MASS, UMass, IPAC-Caltech, NASA, NSF

The M52 cluster in the constellation of Cassiopeia is only about 19 light years in diameter. However, it’s tidal radius, which is the area in which its gravitational influence is dominant, spans across about 42 light years. While this is kind of average for open star clusters, the really remarkable aspect of this cluster is the number of variable stars it contains. For instance, the cluster contains 18 slowly pulsating B-class stars, and three suspected γ Dor variable stars. Another remarkable aspect is the lack of interstellar material in the cluster’s inner regions, which suggests that several supernova events had occurred early in the cluster’s life- each successive blast blowing progressively more material out of the cluster’s core.

 Messier 103 (NGC 581)

Credit: 2MASS, UMass, IPAC-Caltech, NASA, NSF

Located about 9,500 light years away, this cluster has only about 40 or so member stars (depending on the source consulted). However, it is still in the general area within the constellation Cassiopeia where several thousand such small, compact clusters had formed at roughly the same time. Many or most of these clusters have dispersed in the intervening 25 million years, but fortunately M103 has not, and it is still an easy binocular target.

The White Rose Cluster (NGC 7789)

Located about 8,000 light years away, this pretty cluster was discovered by Caroline Herschel, and is popularly known as the White Rose Cluster. This is due to the arrangement of dense knot of stars and voids that create the impression of rose petals. The predominantly yellow stars tell us something of the cluster’s age; estimated to be about 1.6 billion years old, most of the stars in the cluster have evolved off the main sequence, and are now in their red or yellow giant phases. As a matter of interest, this cluster spans across 50 light years, which from our perspective, appears to be equal to the diameter of the full Moon when viewed through binoculars.

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