September 2021 Skies

I really love the sky in September. Spring is in the air – so the songwriter claims and the flowers are starting to bloom, but more importantly, the night sky is incredible. The nights are starting to get slightly longer, which is good because we can spend more time outside without being as cold.

While in Australia, the season officially starts on September 1; astronomically, it will not start until September 23, the Spring or Vernal Equinox. The Equinox occurs when the Sun is directly above the Earths equator, which only happens twice a year for an instant of time.

However, for now, let’s think about what is in the sky this month.

The Moon this Month

(All times are in Australian Eastern Standard Time)

  • New Moon: 11:00 am September 7th
  • First Quarter: 07:00 am September 14th
  • Full Moon: 10:00 am September 21st
  • Last quarter: 12:00 pm September 29th

The new Moon occurs when the Sun and Moon are aligned. Therefore, the Moon is invisible from Earth, creating the darkest time of the month to go outside and enjoy the sky.

On the 11h at 8 pm AEST, the Moon will be at perigee – the closest it comes to Earth this month– being a mere 368,461 km away from us. On the 27th at 8 am, it will be at its furthest point or apogee when it is 404,640  away from us.

From the 8th to the 10th, look for the slender crescent moon in your western sky in early twilight.  On the 9th, it will be close to Mercury in the early evening, while on the 10th, it will be close to Venus.

Figure 1: Early evening sky 9 September 6:10pm AEST

Planets in September

MERCURY – This is the best time to see Mercury if you have a dark western sky free of light pollution in the early evening. It will be moving through Virgo this month, and on the 21st, it will be very close to Virgo’s brightest star Spica. They will be separated by three times the width of your little finger, the width of your little finger is about half a degree, and if you were to hold it up, it would cover the full Moon.

And Mercury will be slightly brighter than Spica, which is unusual since Spica is the 16th brightest star in the night sky. Although it appears as a single star, it is a spectroscopic binary, and we can only see it as one star.

Just a few days later, Mercury will reach its greatest height above the horizon

VENUS is hard to miss high in the western evening sky, spending the first half of the month in Virgo before moving into Libra. It will be less than 2 degrees from Spica on the 5th and 6th, so you can use Venus to find Spica.

It is incredibly bright, and you can understand why it is known as the ‘Evening Star’. It will provide a good photo opportunity on the 10th when the four-day-old waxing crescent moon is only 4 degrees away. If you have a good pair of binoculars, try and have a look at Alpha-Libra, the brightest star in the constellation of Libra. It will be close to Venus on the 24th, and it is a lovely little double star with both yellow and white star components.

EARTH reaches the Spring Equinox at 5:20 am on the 23rd September Australian Eastern Standard Time, and from any place on Earth, the Sun rises in the East and sets to West.

This is when day and night are roughly equal in duration. It is the actual instant of time when the plane of Earth’s equator passes through the geometric centre of the Sun’s disk. An equinox occurs twice each year, around March 20 and September 23. This is the exact time at which the centre of the visible Sun is directly above the equator.

Figure 2: Equinox and Soltices

MARS can no longer be seen this month as it reaches conjunction with the Sun on the 8th. It starts the month very low on the western horizon. You might be able to catch it early in the month, but as its setting in the twilight, but you will have to have a perfect western horizon.

It will remain hidden in the Sun’s glare until late November when it will reappear in the eastern dawn sky.

JUPITER is with Saturn in the constellation of Capricorn high in the North Eastern evening sky. It is now well past opposition, but the naked eye is scarcely noticeable, but the planet size and brightness decrease. Most of you won’t even notice it. Even in binoculars (if you can keep them steady), you can see its four Galilean moons. If using binoculars, it is probably a good idea to put them on a tripod. It is great to watch the dance of the moons as they move around Jupiter during the night. Check them out either every hour or so or each night. Make like Galileo and keep records of their location from night to night.

Watching the dance of Jupiter’s moons is something I never get tired of. Along with watching the red spot, which does require a reasonably size telescope to see.

On the 18th, the waxing gibbous Moon will be only 4 degrees from Jupiter, so again, excellent photo opportunity.

Figure 3: Evening sky 18 September 7:15pm

SATURN is very high now in the Eastern sky after dark.

This month try looking for the shadow; if you have access to a telescope. Looking for the shadow on the back of the rings is pretty cool. You are unable to see this when Saturn is at opposition as it is behind the planet. It gives you a 3d effect, and there will be an excellent opportunity to see this in October early November.

URANUS rises in the mid-Eastern evening sky in the constellation of Aries in the morning hours. You may want to get up about 2 am on the 25th when you should be able to find it quite easily. This is because it will only be half a degree or the width of your little finger from the rim of the Waning gibbous Moon.

It is much easier to find both Uranus and Neptune in binoculars or a telescope if you have something to start looking from, and the Moon is a good starting point

NEPTUNE is at opposition on the 14th and is visible in the constellation of Aquarius but will be challenging to see as it is the early morning twilight.

To add a little bit of interesting trivia. Neptune was in the same constellation (Aquarius) in 1846 when Galle discovered the planet. So Neptune has completed one orbit of the Sun since it was found. That orbit was completed in 2011. It can little bit of a challenge to find. You most likely will need at least a 4inch telescope and about 200 power of resolution to a see it as a small blue disc but it is still pretty fun to try and find it.

Figure 4: Morning sky 25 September 2:25am

Meteor Showers

The month starts with a minor meteor shower called Alpha Aurigids. It is not a brilliant one for us down under, but it is worth looking at if you are up and about at 3 or 4 am. You may get to see 6-8 extra meteors. Some of them can be pretty bright. The easiest way to see it is, of course, to get up and go outside, keep warm and do all the usual sorts of things to do with watching a meteor shower.

The best idea is to look towards the North East to see a crazy, very bright star called Capella. It looks like this because it is low on the horizon. I tend to call it the disco star because it looks like a disco star. Work your way from that and look towards the North East, where the radiant of the meteor shower will be.

Usually, a small number of “sporadic” meteors can be seen each hour of a moonless night. Sporadics are likely to be seen in any part of the sky. During a shower, the number of meteors visible may increase considerably. The meteors will appear to originate from a small area of the sky, called the radiant. The spreading out from the radiant is a perspective effect due to the meteors travelling in parallel lines. Still, as they approach the observer, they appear to fan out. The shower is named after the constellation, which contains the radiant. In general, the meteor trails do not start from the radiant, but a few degrees from it.

Clear skies until next month! Stay up to date on my Facebook page.

PS: Why not grab the 2022 Astronomy calendar which also includes the amazing photos and information on the planets, moon phases and skymaps for each month –$19.95

Donna the Astronomer

I am a keen astronomer lucky enough to live and work in Coonabarabran the Astronomy Capital of Australia! I am a ‘Drover’s Brat’ and discoverer of a couple of comets and asteroids. I operate Milroy Observatory and can show you how to best integrate dark sky experiences into your tourism, farm stay or AirBnB business.

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