The Summer Triangle

I have been meaning to write on this subject for some time.  I have made reference to the Summer Triangle many times through my blog postings and never took the time to adequately define it.  It stands above our heads during the Summer months and is an indicator of the season.

There is quite a curious history behind this asterism.  It is believed that the first reference to the 'Summer Triangle' in literature is by H.A. Rey in his 1954 book "Find the Constellations".  Although more famous for his Curious George series, he spent a lot of time working on astronomy books for children.  They are still a good reference today.

The Summer Triangle simply consists of three very bright northern stars forming a triangle in the sky.

Vega (Alpha Lyrae) - This is the brightest star in the constellation of Lyra the Lyre.  It is the fifth brightest star in the sky.  At a distance of 25 light years from Earth it is considered a close neighbour.  Vega is also circumpolar for observers in Calgary; it always stays above the horizon but just barely.  It is a class A star which means it generally has a white hue to it for observers.  Vega is the star that plays a significant role in the 1997 movie 'Contact'.

Deneb (Alpha Cygni) - This is the brightest star in the constellation of Cygnus the Swan.  It is a very luminous star and appears around magnitude 1.25.  However, unlike Vega, Deneb is 2600 light years away.  To be in the top 20 brightest stars in the sky at this distance is remarkable.  Also, like Vega, it is circumpolar from Calgary and will not tuck in below the horizon.  As a class A star it will seem white to the observer.

Altair (Alpha Aquilae) - The twelfth brightest star in the sky lights up the constellation of Aquila the Eagle.  Altair is, in fact, closer than Vega sitting around 17 light years away.  It is the southernmost star in the Summer Triangle and will drop below the horizon at certain times of the year.  Like its compatriots of the triad it is class A and will appear white.

The map below shows this triangle in the sky in the middle of August at 11pm.  Look directly up and a little bit to the South to see this pattern.

The Summer Triangle

I appreciate the Summer Triangle as it is usually the first thing I see during Summer twilight.  Typically the earlier in the evening I can see it the clearer the sky will be for observing.

Cygnus and Lyra are two of my favourite constellations.  Deep-sky objects throughout this region are generally quite easy to locate.  During 2017, I saw several Iridium Flares transit the triangle and once the ISS flew right through.

It is the middle of November and the triangle is still visible in the western sky in the early evening.  However, Summer is on its way out and we will soon be gazing upon the Winter Hexagon.  This will be discussed in the next post.