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  • Rapt in Awe

    My Journey through the Astronomical Year

    Think of this as a "companion text" to this, the main web site. Not required reading, butI hope you'll find it interesting and helpful.

July’s Guidepost Stars: Look east – look south!

July offers an eyeful, and if you are just starting to learn the sky this month, you have four new guidepost stars to meet. However, those who were out in June already met Vega and perhaps the rest of the Summer Triangle – if not, by all means get out about 45 minutes after sunset on a July evening and look to the east. In the twilight you should see something like the simulation below with Vega the highest and brightest of the trio. Altair is next in brightest and the most southerly. Deneb is the least bright of the three and most northerly. This triangle is huge – roughly 20 degrees (two fists) in height and 40 degrees (four fists) in width. And you’ll have plenty of time to get familiar with it, for it’s prominent in northern latitudes right into winter.

 

Summer triangle in twilight, as depicted in Starry Nights software. Be sure to click for larger image.

Summer triangle in twilight, as depicted in Starry Nights software. Be sure to click for larger image.

 

 

But once you feel confident you have this triangle identified, face South and look for our other July guidepost star, Antares. The name “Antares” can be translated as “rival of Mars” and is an indication of the star’s redness. If this isn’t immediately apparent to you, compare it to blue/white Vega. Or, if you have been studying the sky for several months, compare it to the icy blue of Spica, now in the southwest sky. (Remember – you reach Spica by following the arc of the Big Dipper’s handle first to Arcturus, then continuing on to Spica. 

 

Stellarium's depiction of the twilight sky looking due south in July from mid-northern latitudes. Antares is the bright star to the left (east) and Spica the other one. Click for a much larger image.

Stellarium's depiction of the twilight sky looking due south in July from mid-northern latitudes. Antares is the bright star to the left (east) and Spica the other one. Click for a much larger image.

 

 

The image above shows how the twilight sky to the south looks in early July. The lower star on the left is Antares, the one to the right is Spica. There’s about 45 degrees between these two, so as it gets fully dark you’ll notice Antares is almost due South. In northern latitudes Antares is quite low – here in Westport, MA. it is only 22 degrees above the southern horizon when it transits (about 10 pm in early July) – just half as high as Polaris which, of course, anchors the northern sky. (No – Antares is not the southern pole star. It is a long way from it. In fact, there is no bright star marking the southern celestial pole, but if there were you would have to be in the southern hemisphere to see it. Antares is less than one third of the way to the South Celestial Pole. )

As the sky gets fully dark on a July evening, Antares will be due South and be the core of one of the constellations that really does resemble it’s name – Scorpius, the scorpion.

Antares at the heart of Scorpius.

Antares at the heart of Scorpius.

The stick figure charted at right doesn’t really do justice to the graceful curves of its body and tail. Sadly, for me this constellation is largely hidden by trees. My best view of Scorpius comes when I look to the south over the bay or ocean, though I can see it early on a July evening if I step out into the road in front of my house, for the road heads south and at that time Scorpius dominates my southern sky from the horizon to about one third of the way up.

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