The Night Sky This Month: September 2019

Image credit: NASA, JPL-Caltech, MSSS

The September Equinox occurs at 07:50 UTC on the 23rd of September. On this date, the Sun will be directly over the equator and as a result, the day and night of September 23rd will be almost exactly the same length throughout most of the world. The September Equinox marks the first day of autumn in the northern hemisphere, and the first day of spring in the southern hemisphere.

Constellations that are prominent in the mid to late evening sky in September include Cygnus, Aquila Lyra, Perseus, and Cassiopeia, with the Great Square of Pegasus to the eastward of Cygnus. The “Summer Triangle” is also prominent, as is Andromeda, which contains M31, also known as the Andromeda Nebula.

Mars Curiosity

Mars has been the focus of so much scientific interest of late. Therefore, let’s take a moment to reflect on the Mars Curiosity rover, which landed on the Red Planet in 2012. The image above shows the Mars Curiosity rover “looking” back along the 12 km-long tracks it has left on the Martian surface since that landing on August 6th. In this image, the tracks seem to originate at the Vera Rubin ridge, which was named after Vera Rubin, who had discovered that the outer parts of galaxies rotate much faster than the general structure of galaxies allows. Rubin’s discovery lead to the concept of “Dark Matter”, a mysterious form of matter that appears to “freeze” galaxies, which explains the almost uniform rotation curves of galaxies.

The Moon Phases In September 2019

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

The Planets In September 2019

The month of September does not offer much in the way of planetary viewing. For observers that are up for a challenge, though, some details of what to expect are given below:

Mercury reaches a point of superior conjunction with the Sun on the night of September 3rd/4th. It will therefore not be visible for the entire month. 

Venus is now just emerging from behind the Sun, and by month’s end, the planet will set in the west south-west barely thirty minutes or so after sunset. As a result, Venus will be difficult to spot. This is due to its close proximity to the Sun, and also the fact it will not rise above 10 degrees or so above the horizon beacause to the shallow angle between the horizon and the ecliptic.

Mars reaches a position of superior conjunction with the Sun on the second day of the month. Consequently, it will be hidden behind the Sun until the end of October. Note that Mars will next appear as a bright predawn object.

Jupiter starts the month shining at magnitude -2.2 in the south, after sunset. Having ended its retrograde motion, the King of the planets is now receding from its position close to the bright star Antares in Scorpius. However, Jupiter is still falling towards the south, and it will thus not rise above about 13 degrees when it transits the meridian.

Nonetheless, observers using small telescopes fitted with an atmospheric dispersion corrector will be able to view the Great Red Spot on the following dates and (BST) times-

September 1st    –    20:17         September 15th –   21:53

September 3rd   –     21:55         September 20th –   21:03

September 8th    –     21:05         September 22nd –   22:42

September 10th –    22:44          September 27th –   21:52

September 13th   – 20:14          September 29th –   23:31

Saturn starts the month shining at magnitude +0.3, which reduces to magnitude +0.5, while its angular diameter reduces to 16.9 seconds of arc as the month wears on. Note though that Saturn is now in the far southern reaches of the constellation Sagittarius, and will therefore not rise above about 14 degrees when it crosses the meridian. As with Jupiter, an atmospheric dispersion corrector will be required to obtain reasonably clear views of the planet and its ring system.

Neptune is now visible close to the star Phi Aquarii, but note that large telescopes with apertures of 8+ inches will be required to resolve the blue-grey hue of the planet’s disc. Observers that have suitable equipment will find Neptune about 13 seconds of arc away from the star Phi Aquarii on the night of September 5th/6th. Note that since Neptune will be at its closest approach to Earth on September 9th, the planet will be visible throughout the night.

Meteor Showers in September 2019

No significant meteor showers or increased meteor activity is expected to occur during September.

Deep Sky Objects to Look For In September 2019

This month, we take the opportunity to explore a variety of spectacular deep sky objects that are to be found in the constellations of Andromeda, Lyra, and Cassiopeia. The three objects listed below are Messier objects, all of which are easy to find and observe with modest amateur equipment.

Messier 32 (Le Gentil, NGC 221)

Messier 32
Image credit: NASA

Located about 2.65 million light years away in the constellation Andromeda, this elliptical galaxy was the first such galaxy to be discovered. From our perspective, M32 appears to be spread out over much of the central regions of the larger Andromeda Galaxy, and is therefore believed to be located between us and the Andromeda Galaxy. Due to its location, M32 is widely believed to have been much bigger than it is now, since it appears to be losing stars, gas, and dust to the more massive Andromeda Galaxy. Nonetheless, M32 is an easy target for large binoculars and small telescopes because of its high surface brightness.

Messier 52 (NGC 7654)

Messier 52
Image credit: 2MASS, UMass, IPAC-Caltech, NASA, NSF

Located only about 5,000 light years away in the constellation Cassiopeia, this colorful open cluster’s magnitude of 5.0 makes it an easy target for binoculars. The cluster stretches over about 19 light years, and is believed to be relatively young- being only about 35 million years old. Note that the very bright star in the frame is an over-exposed foreground star that is unrelated to the cluster.

Messier 56 (M56, NGC 6779)

Messier 56
Image credit: NASA

Located about 33,000 light years away in the constellation Lyra, M56 is a globular cluster that stretches across about 84 light years, placing it among the largest of the Milky Way’s globular clusters. It is also very old; it is estimated to be about 13.7 billion years old, which means that it must have formed (relatively soon after the birth of the Universe) from the remains of the very first Population I stars to have died.

Look for the cluster in Lyra about midway between the double star Albireo, and the bright star Gamma Lyrae. Note, however, that while large binoculars will reveal a “fuzzy” star, 8-inch and larger telescopes will begin to resolve individual stars in the cluster.

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