Daylight saving has started and the nights are getting shorter. October sees the beginning of the season where Southern Hemisphere astronomers are seriously thinking about taking up solar astronomy as the the opportunities to observe the night sky start competing with the need for sleep. Notwithstanding the unfavourable night sky viewing conditions brought about from the decreasing length of the night, there are still many amazing things to see.
Here are the highlights of the night sky in October, as viewed from mid latitudes in the Southern Hemisphere. That means if you are are located in the lower latitudes of the Northern Hemisphere you’ll still get to see much of the stuff I’ll cover here, just not the patch of sky around the South Celestial Pole.
Have a plan
It’s always good to have a plan for describing the night sky so this one will be starting from biggest and brightest objects and then focusing on some smaller and dimmer objects.
The biggest and brightest
After spending much of the Winter dominating the Southern Sky with the galactic centre being almost straight up, once the Sun goes down at about 7:30pm on the 1st October, the Milky Way will be well on its way to descending to the Western horizon, so look for it in the west. The centre of the Milky Way makes a huge X shape with the path of the Ecliptic, the cross over point being Scorpius and Sagittarius.
Arranged along the ecliptic are the constellations of the zodiac, with Virgo on the horizon hosting the Sun and at the other end Pisces, just starting to rise. In the middle, above our heads, are Scorpius and Sagittarius marking out the area which is the galactic centre and home to the Super Massive Black Hole (SMBH) at the centre of our galaxy, called Sagittarius A* (pronounced Sagittarius A star).
The satellite galaxies
To the South lies the South Celestial Pole, the centre point that the whole Southern Sky rotates around. This is as high in the sky as your local latitude, but unlike in the Northern Hemisphere, where Polaris gives an indication for the North Celestial Pole, here there’s no naked eye star to mark it.
The two satellite galaxies of the Milky Way, the Large and Small Magellanic Clouds spin around the South Celestial Pole. During winter, after sunset, they have been closer to the horizon, but as we get into summer they will increasingly get higher in the sky as they cycle through a more favourable viewing position on the Northern side of the South Celestial Pole.
After sunset, at the start of the month, the Small Magellanic Cloud is in a reasonable position to observe with the naked eye, except in places with significant light pollution. The Large Magellanic Cloud is not in an ideal position until much later in the night towards the morning but this will steadily improve throughout the month.
The Northern Summer Triangle
Towards the North, the bright star Vega reaches its highest point from this latitude at only about 10 degrees above the horizon. Between Vega and the North Eastern direction are many objects familiar to observers in the Northern Hemisphere such as, the Coat Hanger asterism, Dumbbell Nebula, M15 and M2 globular clusters.
As the evening advances, the North American Nebula will graze the horizon but you’ll need an almost perfect horizon to capture an image of that stunning nebula. At about 10pm on the 1st October you’ll see two bright stars right on the Northern horizon, Deneb and Vega, these two stars make up one side of what is known, in the Northern Hemisphere, as the summer triangle. The third star of this asterism is Altair which is about 40 degrees up towards the zenith. This triangle gives some idea of the overlap between the Northern and Southern skies. From Deneb to the North Celestial Pole is about 45 degrees.
Approaching the Zenith in the evening is the very interesting constellation of Grus, the crane, which has a very distinctive line of pairs of stars. As the evening advances the constellation gets higher and higher. To the right of the line of bright pairs of stars is the magnitude 1.8 star Alnair. This constellation can be helpful in finding the Small Magellanic Cloud If you follow the curved line away from the ecliptic for about 25 degrees you’ll come across our small satellite galaxy.
The really cool thing about this constellation is that the colours of its stars are subtly visible, from hot white stars to slight redder giants and a few yellow stars thrown in for some variation.
The Milky Way
The Southern Cross is doing its big descent as it dives towards the horizon, getting lower and lower each evening throughout the month, as seen after sunset. It is circumpolar so it never disappears from the Southern Sky but it means the lovely clusters and nebulae that you would have enjoyed in Spring and Winter have long gone from being in a favourable viewing position — they now compete with the horizon.
The other patch of the Milky Way that remains in a very good position for viewing is the area around Sagittarius and Scorpius with many globular clusters and nebulae (distant, celestial clouds) to look at. The highlights, for me, are the bright nebulae such M16 (the Eagle Nebula), Lagoon Nebula and the very photogenic Triffid Nebula. Ptolemy’s Cluster is a great naked eye object that is visible between the two constellations.
The Helix Nebula
One of my favourite objects of the night sky is the Helix Nebula, which is in a great position to view at this time of the year. It sits between Aquarius and Capricornus and is a challenging object to view. Counter intuitively it is best viewed with binoculars or with a large eyepiece in a telescope. Because it has a relatively low surface brightness, it is quite hard to pick out against the background sky and looks like a faint disk.
This object really comes alive when photographed as the ring structure and filaments can be captured quite easily. It is one of the closest planetary nebula to us at about 700 light years, which is why it appears so big to observers.
Meanwhile in Pavo…
In the constellation of Pavo, in the South towards the Milky Way, are two very nice objects to view with a telescope. One is NGC6744 galaxy and the other is the lovely globular cluster NGC6752. Like all galaxies it is a challenge to easily see without the aid of reasonable telescope but this one has a bright core which will look like a fuzzy disk. Depending on the conditions, you might get a hint of the extent of this galaxy. In photographs, it is a complex spiral with many arms and astronomers think it is probably very similar to how our very own Milky Way looks.
The other object in Pavo is quite different and a really nice globular cluster to view. It has a bright blue star in the foreground with the tightly packed globular appearing just next to it. You’ll still need a small telescope to see this one though.
Make the most of it
As the month progresses all of this objects will slightly change in their positions as the Milky Way starts to line up with the horizon and Orion begins its appearance in the night sky. Make the most of viewing the area around the galactic centre now, as this will be too low on the horizon as we move into November.