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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.

Vega brings us the Summer Triangle – and continues to do so right into winter!

Vega is the guidepost star for June, heralding the rising of the Summer Triangle which stays with us right until winter! Look for it in the eastern sky about 45 minutes after sunset. (Click for much larger image.)

Vega is the guidepost star for June, heralding the rising of the Summer Triangle which stays with us right until winter! Look for it in the eastern sky about 45 minutes after sunset. (Click for much larger image.)

In these June nights when it isn’t really dark untila fter 10 pm  – at least for those of us on Daylight Savings Time – the Big Dipper pointing  to Arcturus and Spica are still high inthe sky, but brilliant Vega – magnitude zero – is well up in the east and bringing with it the other two stars of the Summer Triangle.  Deneb and Altair.  We’ll focus on those two next month. This month it’s enough to remind yourself of where to find Arcturus and Spica, then move on to Vega. And while you’re at it, see if you can notice the color difference between Arcturus and Vega – but wait until Vega is high enough so it now longer twinkles and changes color in the thick atmosphere near the horizon.

We call these three the “summer” triangle, but the truth is, they dominate our sky for a full six motnhs. You can see them in the east  on the night of the Summer Solstice – June 21 – and in the West around the Winter Solstice near Christmas. In fact, they’re stillt here a month later, but by then Altair is starting to get lost in the twilight, though Vega is still high enough in the northwest to see easily.

Add a couple of asterisms!

While I feel the guidepost stars are the most important to learn, if you really want to find your way about the night sky it’s also helpful to learn some key asterisms.  For June there are two to add to your memoru banks – the Keystone of Hercules and  the half circle of stars thata re the core of Coronoa Borealis – the Northern Crown.

Once the sky has really darkened on a June evening, look for the Keystone and the Crown on a line drawn between the two, bright guideposts stars of Arcturus and Vega.  (Click image for much larger chart.)

Once the sky has really darkened on a June evening, look for the Keystone and the Crown on a line drawn between the two, bright guideposts stars of Arcturus and Vega. (Click image for much larger chart.)

Once the sky has really darkened – between 10 and 10:30 on June evenings in Westport, MA  – draw an imaginary line between Vega and Arcturus.

Now look for our two helpful asterisms along this line.

The Keystone of Hercules is made up of four stars of magnitude 3-4 that form a perfect keystone, its narrow end to the south. (The star in the southeast corner is faintest – magnitude 4. The star in the southwest corner is the brightest.)

The second asterism to seek out, the Northern Crown, has one really bright star of second magnitude. Its other stars are magnitude four and five, so your eyes must be dark adapted to see this. If you live in suburban, light-polluted skies, try this. Find its brightest star, then with binoculars look first for the arc of three stars trailing off to the east, then the arc of two stars to the west of this dominant star.

Note: The typical binocular field will capture just half of this asterism at a time.

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