Sep 2018

Miulky Way/Summer Triangle last hurrah

Summer Triangle: Best in Autumn
by John Hlynialuk
Bluewater Astronomical Society

In October, we are officially into fall but the night sky is still in summer mode. The two summer astronomical objects on prominent display are the summer Milky Way and the Summer Triangle, and it will be well into winter before both disappear below the western horizon. So let’s say a proper goodbye to the summertime night sky.


For the next few months, when clouds part long enough at night for you to see anything, the Milky Way stands vertically over the SW horizon and stretches overhead and behind you. At a dark sky location, you can follow the glow of our home galaxy right to the northeastern horizon. Star charts are available on the BAS website under the CHARTS/FORMS tab and also at and an all-sky chart is included here. Start by looking southwards and locate the most obvious patch of Milky Way just above the southwestern horizon. The constellation there is Sagittarius, looking like a teapot tipped somewhat to the right. Say a hello in passing to Saturn just off the lid of the teapot. Now follow the Milky Way glow up to Aquila and overhead to Cygnus. Then turn around, face north and continue down past Cassiopeia to Perseus low above the northeastern horizon. At a dark site you should be able to trace the glow of the millions of stars that make up the Milky Way from horizon to horizon. The glow is more obvious in Sagittarius because you are looking itoward the centre of the galaxy where more stars are concentrated. In the opposite direction, looking past Perseus, you are gazing out into the less starry regions beyond the edge of our home in the Universe.

To locate the Summer Triangle, find the bright “alpha” stars of Cygnus, Lyra and Aquila. This is not hard as these constellations are straight up at the zenith right now. Look for the three brightest stars that together form a large right-angled triangle. Those stars are Deneb, Vega and Altair, -hints are on the chart.

It will be several months before this asterism disappears completely and even at years-end, Deneb will still be visible before midnight above the NW horizon. In December, of course, no one will be thinking about summer and the only “Milky Way” will probably be steam rising from mugs of hot chocolate as hardy stargazers check out our winter constellations.

As for other sky objects, there are only two bright planets left in the night sky, Mars and Saturn. Venus is lost in solar glare low in the west and Jupiter is close behind. Both drop quickly into the western sunset glow and by 9 pm, the time of the included chart, both have disappeared. The remaining planets, Saturn and Mars, are not labelled on the chart but they are not hard to find, -both are bright enough to be the first “stars” you see at night.

Let’s hope for a few nice, not too frosty, autumn nights to catch the last of the offerings of the summer sky. And if it is too cloudy, do some armchair astronomy by reading my weblog on the BAS website.

Clear skies!