September

Instructions to read before looking up – September night sky
  • Learn what is September and what we do with it,
  • Find out what’s the Sun up to,
  • Find out what’s in the Milky Way,
  • Find out what Orion and Scorpius are up to
  • Find out what are the brightest stars visible at night after sunset and finally find out about our favourite binocular and telescope objects.

A bit about September

September comes from Latin word “septem”, which means “seven.” In the old Roman calendar it was the 7th month, rather than 9th as it is today, counting from March, which was considered the beginning of the year. Traditionally, September is linked to harvest in the Northern hemisphere as it was the month of harvest. From apples to grapes, most autumn fruits were getting ripe then. Especially the harvest of the grapes was always a good reason to celebrate.

The overarching deities this month were in charge of agriculture and abundance. Since the 10th century BC, that’s 12,000 years ago, Babylonian Goddess Shala and her ear of grain (now the star Spica) associated with fertility was ruling the sky in September. The Early Greek observed Demeter, their goddess of wheat and agriculture and the Romans Ceres. So it was the same theme repeating, which was related to harvest. Of course, here in the Southern Hemisphere none of these happen and in September all the flowers are in bloom.

Interesting to note is that the corresponding stars for these constellations are at this time of the year very close to the Sun, thus we cannot actually see them and they are best visible six months later when they reach the highest position in the sky. If we look at the zodiacal constellations where the Sun lays, in September, the Sun transits through Leo until the 17th when it moves into Virgo where it stays until October 31st.

The zodiacal constellations are those stars visible behind the plane of our Solar System, about 8 degrees each side of the ecliptic. They form a band in the sky, called the Zodiacal Band.

The Sun in Virgo means only one thing: opposite the Sun (that 180 degrees on the other side of the zodiacal band) is Pisces. Pisces will rise just after sunset and be visible all night long.

You are not who you think you are ...
The Zodiacal band, an awesome drawing by Eugene Georgiades. Zodiac signs from most newspapers are not in sync with the real position of the Sun transiting through the zodiacal constellations.

September is also when we celebrate the equinox, when the day is equal to the night.

Equinox is the moment in time when the plane (extended indefinitely in all directions) of Earth‘s equator passes through the geometric centre of the Sun’s disk. From Earth, the centre of the visible Sun will be directly above the equator. The projection of Earth’s equator in the sky is known as the celestial equator.

The September equinox along with the March equinox are the two days when the Sun rises exactly from the east and sets in the west.

Before Stonehenge Aotearoa was built the team had to measure the position of the Sun and stars to align the observatory precisely to its location in New Zealand. Here the Sun is rising exactly from the East at equinox. As seen from the centre of the henge today, a pou marks the position of the Sun at sunrise.

After September Equinox, as seen from Earth, the Sun now will lean towards the southern part of the sky. For us, it will appear higher and higher in the sky. Seen from space, South Pole will lean towards the Sun, receiving more sunlight, which will warm the atmosphere up.

At equinoxes, the Sun will set directly on top of the background pillar

The First point of Libra

These fancy words are naming the point on the celestial map where from Earth it looks like the Sun shifts celestial hemispheres. As we look at the Sun from Earth, every day it seems to change its position in relation to the background stars. There are two main lines on a celestial map, the celestial equator (see above) and the ecliptic. They cross at equinoxes. 2000 years ago this point was in Libra. Due to Earth’s wobble, which has a spinning top movement, this point shifted now and is in Virgo. In 400 years from now it will be in Leo.

The equinox is only a moment in time as Earth continuously moves as it orbits around the Sun. In our case, from this point forward the Sun will be in the South Celestial Hemisphere for half a year.

While it takes thousands of years for us to see the proper motion of stars, which makes stars such reliable time keepers, Earth’s wobble, known as precession makes the equinox points to change. Which is why, traditionally the September equinox point is even now called the First Point of Libra but the crossover occurs within the boundaries of Virgo very close to the star β Virginis. From the 18th century to the 4th century BC, the Sun was in Libra on the autumnal equinox, shifting into Virgo after that. This point will pass into the neighbouring constellation of Leo around the year 2440.

Seasons. The green line is the extension of Earth’s axis in the sky. The lean of the axis does not change thus as it goes around the Sun.

September has 30 days.

What’s the Sun up to?

The Sun rises at 6:42 am on the first day of September and earlier and earlier every day so that on the 26th of September it will rise at 6:00 AM. However, the clock will shift by one hour on the night of the 26 of September so on the 27th of September it will rise at 6:58 am. The sun sets at 5:53 PM on the 1st of September and later and at 7:22 PM on the 30th of September.
According to TimeandDate.com, September Equinox in Wellington, New Zealand is on Wednesday, 23 September 2020 at 1:30 a.m. NZST. As the month goes, the days will be longer than the nights until we reach Summer Solstice. Since the equinoxes only occur twice per year they are very special astronomical events.

Disclaimer:

It’s dangerous to look into the Sun!!

Of course, if you have solar telescope, that is well maintained and is designed for looking at the Sun, then you can look at the Sun.

Spring begins on the 1st of September

Since 1870s New Zealand used the meteorological dates to mark the beginning of spring, thus spring here begins on the 1st of September!

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In New Zealand we are entitled to have an opinion about when spring starts. (21st of September however is NOT the day of the equinox). Source: Stuff.co.nz.

People who come here from the Northern Hemisphere usually think that spring begins at the autumnal equinox. But just for the sake of the argument, according to WeatherWatch Managing Director Philip Duncan, there are actually four ways to start a season (1) looking at astronomical dates, which would place the date on September 22 or 23, based on the equinox, (2) by meteorological dates – which is a three-month division of the year into seasons, thus Spring starts on September 1, (3) observing the solar winter, which is the three “darkest” months with the June 21-22 winter solstice in the middle, which shifts the beginning of spring to August 8 and (4) looking at what nature does, which in New Zealand is hard to pin down.

The Milky Way and Zodiacal Light

Here in Aotearoa, in September, the asterism of Scorpius is at this time of the year the Fishhook of Maui that drags the Milky Way down from the sky. We still get to admire the amazing galactic centre and the Milky-Way.kiwi inside it.

Many cultures and languages have various names for the Milky Way. In Kazakh, the Milky Way is called “құс жолы,” meaning the “bird’s road” (Alina Sabyr). In addition to the Milky Way, if you are stargazing from somewhere with very dark skies, you can spot what is called the “Zodiacal Light” It’s a cone-shaped light that stretches from low on horizon along the ecliptic. The ecliptic marks the plane of our solar system bearing the zodiacal constellations. The ecliptic is “a great circle on the celestial sphere representing the Sun’s apparent path during the year, so called because lunar and solar eclipses can only occur when the moon crosses it. The zodiacal light is the light we see reflected from dust and ice particles in the plane of our own solar system! How cool is that? So in the sky we can see both the galaxy that we inhabit and the solar system. Two completely different scales! And it again very confusing as they are in different parts of the sky. But the part of the sky where we observe the Zodiacal Light, is where the ecliptic would be.


By the way, did you know that the famous Brian May from Queen did his PhD in astrophysics studying spectroscopic studies of the motion of the dust responsible for the zodiacal light? Here is a very cool video of scientist Dr. Rebecca Smethurst in which she explains it.


The centre of the Milky Way: Scorpius, Centaurus and Southern Cross

At this time of the year, in Aotearoa, the Māori names for Scorpius is Te Matau A Maui – the fishhook of Maui that drags the Milky Way from the sky all night long. This is alluding to the fact that after sunset you can see the fish hook at Zenith and then falling down towards the western part of the sky.

The constellation Scorpius has a magnificent red supergiant star Antares. It is impossible to miss on a clear night. It looks quite reddish, just like planet Mars! In fact, its name is derived from Greek, meaning “rival to Ares,” Ares being the Greek name of Mars.

This is a direct image we took in August 2020 of the red giant star Antares with https://star-safari.nz/slooh/

Scorpius has some fabulous deep sky objects. The ones below were taken with Slooh telescopes in August 2020.

South of Scorpius you can find the constellation of Centaurus, a creature that is half-human and half-horse in Greek mythology. Although the constellation itself is more difficult to discern, it contains two very well known star systems in the southern hemisphere: Alpha and Beta Centauri. Alpha Centauri is the closest star system to Earth! It’s about 4.37 light years away so it takes light about 4.37 years to reach it. As a reference, it takes about 8 minutes for light to reach us from the Sun! It is a triple star system and there was an exoplanet discovered orbiting Proxima Centauri, one of the three stars in this system.

Alpha and Beta Centauri can be used as pointers to what is arguably the most well-known constellation in the southern hemisphere, the Southern Cross or Crux. It is on the New Zealand flag! It is seen year-round in New Zealand, and is a circumpolar object in New Zealand.

Circumpolar objects to New Zealand

What does circumpolar mean?

Circumpolar are objects that rotate around the celestial pole.  These objects are above the horizon at all times in a given latitude. For instance Casiopeea is circumpolar from Europe but here in Wellington we cannot even see it, it’s hidden by the Earth. We could if Earth would have been transparent. Here on the other hand we have the Southern Cross with the pointers that are circumpolar.

The Diamond Cross and the False Cross are circumpolar too. Canopus and Achernar are also circumpolar. The same for the Magellanic Clouds, Omega Centauri, 47 Tucanae, the Jewel Box, the Southern Pleiades, the Gem Cluster and Omicron Velorum. Being circumpolar it means they turn around once every 23 hours and 56 minutes. That’s why they are always somewhere else in the sky.

In September, in the evenings, you will find the Southern Cross in the south western part of the sky. So just after sunset is at the 3 o’clock position heading down followed by the pointers. Canopus would be at the same time grazing the southern horizon so hard to see from hilly Wellington. Achernar and the two Magellanic Clouds would be in the south eastern part of the sky.

The edge of the Milky Way: Orion and Taurus

As it is opposite Scorpius on the Celestial Sphere, Orion will appear in the Eastern horizon as Scorpius sets in the western horizon, and at this time of the year we see it in the early morning sky. Earlier than Orion we can observe the Pleiades and the Hyades. Below is the star Betelgeuse, image taken with Slooh.

Some other bright stars

As seen from New Zealand, the ecliptic runs through the northern part of the sky. That’s why everyone here looks for houses facing north as it’s the sunniest part of the sky. Virgo is very close to the Sun and will be visible only in the first part of the month, with the beautiful star Spica sinking beyond the horizon by the middle of the month. We can also see the stars Zubenelgenubi and Zubeneschamali in Libra, and Nunki in Sagittarius.

Nunki. Sigma Sagitarii. Photo Slooh

Starting from the centre of the Galaxy, to the north Shaula, the stinger of Scorpius is a bright star and going south Atria in Triangulum Australe is prominent.

Oldies but Goldies – famous in the North

In the north, we can see the bright star Altair in Aquila, the constellation of the eagle, a triangle-shaped constellation in north-eastern skies. Lower on the northern horizon, mirroring somewhat Canopus, the second brightest star in the sky which is lower on the southern horizon, is Vega, nicknamed Antopus by the awesome Ian Cooper. This is a play of words with Antares, which means the rival of Mars, Ian says that Vega rises low in the north when Canopus is low in the south and they are like two rival eyeing up each other. Another beautiful star is Albireo, in Cygnus (see below). It is a spectacular blue and red giant double.

Vega has a fabulous Messier object which is really easy to see, that is M57 the Ring Nebula, the remnants of a star. In astronomical terms it is a planetary nebula. Another one of its kind, remnants of a star that died is in Vulpecula, M 27 – Dumbell Nebula. All photos below are taken with Slooh.

Dark patches

Other than the Milky Way Kiwi that can be photographed at length this time of the year, the other famous dark patch is the Coalsack, near the Southern Cross. The coalsack is also known as the flounder, which is the Māori name for it. In deed, if you find a truly dark sky, you will see the resemblance.

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The Flounder or the Coalsack, photo: H. Mogosanu. Picture taken at Staveley under a dark sky with a Canon 60D on a tripod.

The Coalsack is an appropriate name, as diamonds are sometimes found in the coal, inside the dark patch, made of interstellar dust matter is the Jewel Box, or the Kappa Crucis Cluster, NGC 4755.

Planets in September 2020

Jupiter and Saturn are in the sky.

Mars is catching up and will soon be at opposition and Venus is in the morning sky, at the beginning of the month is rising around 4:30 AM.