Sky matters; September is the perfect time to spot the Milky Way

SEPTEMBER brings with it the first real inkling that the summer constellations are on the way to being replaced by the generally brighter autumn and winter constellations, writes Niall Smith. 

The nights are getting visibly longer, the temperature is slowly dropping, and the sky itself takes on a crisper appearance as the sun dips farther and farther below the horizon.

It is worthwhile taking some time to sit outside and just soak in the majesty of the cosmos, and if you have reasonably dark skies and allow your eyes to adapt to the dark, which takes about 20 minutes, you should be able to see the Milky Way reaching from horizon to horizon and passing overhead.

It will appear as a kind of ribbon of cloud that remains stationary compared to the stars in which it seems to be embedded. And that’s not a coincidence, because the individual bright stars you can see, and that Milky Way “cloud” are actually all part of our home galaxy.

The “cloud” is composed of billions of stars which are too far away to be seen individually,
but which, when viewed together, merge as if they were somehow continuous.

It would be easy to think of all those stars as being distant and irrelevant, but every atom in your body (with the exception of hydrogen) was built in stars that lived and died billions of years ago in our home galaxy, and without them we would not be here.

So while we think of Earth as home, we shouldn’t forget that Earth exists because our galaxy exists, and that’s probably worth pondering over with a cuppa as you look skywards.

September is also the month of the autumn equinox when the sun is almost directly overhead of the equator and night and day are of equal length for most of us.

This occurs on the 22nd of the month, and will be accompanied by a thin crescent moon which will set around dusk. It should make for a terrific sight.

On September 26, around 9pm, the moon will appear to the upper right of Saturn after sunset, acting as a useful pointer to this wonderful ringed planet.

The planet itself has a yellowish hue and shows little sign of twinkling, unlike the surrounding stars. At about 2pm on the afternoon of September 15, Saturn will be impacted by the Cassini spacecraft which has been in operation for the last 20 years.

The impact will destroy the probe, and the intention is that it will sanitize any bacterial or viral contaminants that may have been inadvertently added to the spacecraft before its launch. Although you won’t be able to see anything on the day — it’s daylight in Ireland and in any case the impact is too small to be picked up from Earth — the next time you do look at Saturn remember that the first alien spaceprobe to enter its atmosphere did so in September 2017 and it came from Earth!

Jupiter, which has been with us through pretty much all of this spring and early summer is now disappearing into the glare of the setting sun and will be difficult to observe for most of the rest of the year.

However, if you look due east around 6.30am during September you will see a bright object, which is Venus, and to the lower left is Mars (which will appear very red, but faint) and Mercury (which will be closest to the horizon).

They will be lined up in a straight line and make for a nice morning wakeup vista!

Did you know?

The sun is so large that 1.3 million Earth’s could fit into it!


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