Life Science September’s skies are filled with cosmic triangles to mark the beginning of spring
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September’s skies are filled with cosmic triangles to mark the beginning of spring

Astronomically, spring starts at the equinoxes, when the line between day and night passes through the north and south poles. Photo: NOAA
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Spring is here and the flowers are starting to bloom.

And while in Australia the season officially started on  September 1astronomically speaking it won’t start until September 22 – thanks to a little astronomical event called an equinox.

This is when the Sun will be directly above the Earth’s equator at noon, and the dividing line between day and night will pass through the north and south poles.

Amazingly, this means that no matter where you are on the planet, daytime and night-time will be approximately of equal length.

At the equinox the Earth’s axis is tilted neither towards nor away from the Sun. This happens twice a year – in March and September.

In places like Australia the September equinox is called the vernal or spring equinox because from this time on the axis begins to tilt in a way that brings the southern hemisphere closer to the Sun.

Well, at least until the summer solstice when the axis movement reverses and nights start getting longer again.

Beyond the gorgeous scent of flowers buzzing with bees, spring is a great time to get out and see the stars at night.

September’s cosmic triangles

“From mid-September to early [October] will be the best time all year to see the planet Mercury in the evening sky,” amateur astronomer Dr Ian Musgrave said.

On September 19 Mercury will form a beautiful cosmic triangle with the crescent Moon and Spica, which is the brightest of nine stars in the constellation of Virgo.

To see it, look due west about an hour after sunset: Spot the crescent Moon, and to its left you’ll see blue-white Spica and a brighter yellow-white Mercury.

“During the month, Mercury rises and gets closer and closer to Spica and by the 22nd September it will be almost on top of Spica,” Dr Musgrave said.

Mercury will form a cosmic triangle with the crescent Moon and the bright star Spica this month. Photo: Ian Musgrave

On September 25 there is another cosmic triangle, this time between the waxing Moon, Jupiter and Saturn.

To see it, look to the north-east, from an hour after sunset. The trio will be very obvious and will be visible all though the night until they set in the early morning.

Mars and Mira put on double bill

Mars shines brightly in the night sky as it gets closer to the Earth on its approach to its closest point next month.

This weekend (September 5-6) Mars will be nice and close to the waning Moon around 10pm.

Later in the month, on September 20 Mars puts on a double bill with the pulsating red giant star called Mira.

The star, which is in the constellation Cetus, will be the brightest in its 330-day cycle on this day.

To see Mira, look for a slightly reddish star just above the eastern horizon about 10pm – it will be two handspans south (to the right) of Mars.

The giant red star Mira will appear to the right of Mars.Photo: Stellarium/Genelle Weule

Venus for the early birds

If you get up nice and early on or around September 14 you’ll see the pretty sight of Venus close to the crescent Moon.

And on September 30, Venus will be close to the star Regulus, which is the brightest star in the constellation of Leo and will be about as bright as Spica.

Both will be visible at 5am, although the Moon-Venus conjunction will be higher an hour before sunrise and easier to see.

Spring stars and galaxies

Sadly, the icon of Australian skies, the Southern Cross, will be harder to see this month.

“The Southern Cross is now quite low on the horizon and is not easily seen, especially late at night,” Dr Musgrave said.

But other stargazing treats await, including the stunning constellation of Scorpius with its massive curling tail, visible from early evening in the west.

From about mid-month and a bit later in the evening, you’ll also see Orion and its belt as it rises over the eastern horizon.

“As Scorpius sets, Orion rises.”

September will also be a good time to see the Small Magellanic Cloud – one of the dwarf galaxies that orbit our own – that will be high in the sky early evening.

To see it, look south in dark skies and measure about six handspans above the horizon to see it.

The Small Magellanic Cloud (right) and globular star cluster 47 Tucanae (left) as seen through a telescope. Photo: NASA: Bogdan Jarzyna

It’ll appear as a wispy cloud if you’re only looking with the naked eye, but at the same time you’ll see the globular cluster of stars called 47 Tucanae to its left.

This tightly packed orb of thousands of ancient stars will probably look like a fuzzy dot, but if you can find some binoculars you’ll see a truly spectacular glowing ball, Dr Musgrave said.

After the spring equinox, nights will only get shorter up until the summer solstice in December, so make the most of your night-time viewing while you can.

-ABC