The Planets in September 2021

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

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

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.

Mars

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

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.

Saturn

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

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

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.

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.

This Post Has 2 Comments

  1. bkellysky

    Wow! I just downloaded http://www.skymaps.com/skymaps/tesms2109.pdf, a map for September’s skies for the southern hemisphere. What a sky! As I just posted on facebook: “The Milky Way arcs high across the evening sky. The center of the galaxy is overhead, Jupiter and Saturn are easily spotted sailing high in the sky. Venus and Mercury are high enough to be easily picked up in the west after sunset. They even can see M13, the wonderful globular cluster in our northern skies. But, who needs that, when they have Omega Centauri, an even better cluster high in their sky (see list on the back of the map).” Wishing you lots of clear skies!!!

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