A summer place

Looking toward the east this week after dark, we see a few bright stars making their way into the sky. These belong to the first string of summer constellations that in another month will assume their place overhead, where the spring stars are now.

We've already mentioned Arcturus in Bootes (see May 10 - 16 and 17 -23), which is practically at the zenith by nightfall. I like to think of Bootes and its adjacent constellation, the little half-circlet of stars to the north known as Corona Borealis, as bridging the spring and summer seasons, because they are prominent in both.

Coming into view around nightfall is Vega of the constellation Lyra the Lyre. Vega is the brilliant blue-white star rising well above the tree-


The rising summer stars ' Looking east-southeast about 10:30 p.m., June 10.









tops toward the northeast. Two and a half times the size of our Sun, Vega is also twice as hot, about 10,000 kelvins. Vega stands near one corner of a group of stars that form a faint parallelogram, which represents the lyre. On July 16, 1850, Vega became the first star ever to be photographed through a telescope. The photograph was made using the 15-inch refractor at the Harvard Observatory in Massachusetts.

More recently, images made at radio wavelengths of Vega show it to be enshrouded in faintly glowing dust, evidence, some astronomers assert, of a budding planetary system. However, given the short lifespan of hot stars like Vega (about 300 million years) planets will likely not have enough time to form. Compare this with our solar system, which took over 4 billion years to condense into planets.

Northeast of Vega is Deneb, brightest star in Cygnus the Swan (also called the Northern Cross). Deneb is one of the largest known super-giant stars. It is about 60,000 times more luminous than the Sun and 25 times as massive. No wonder Deneb is so bright, even at the remote distance of 1,500 light-years.

This Cygnus region is a fascinating one to explore in binoculars since it lies in the thick of the summer Milky Way. By this time next month, it will be higher in the sky, free of the dimming effects of the atmosphere near the horizon, and well placed for viewing. (See July 12 - 18.)

A little after 9:30 p.m., an angry red star rears up far to the southeast. This is Antares in Scorpius. Antares, Greek for 'rival of Mars,' lies at the heart of the mythical scorpion and was one of the royal stars of ancient Persia. In China it was known as the 'fire star.' This reddish star is classified a red giant by astronomers. If Antares were placed where the Sun is now, its huge size would easily swallow up Earth.

Another bright summer star finally breaches the horizon around 10:30 and comes fully into view by 11 p.m. Altair is the brightest star in the constellation Aquila the Eagle. With a distance of only 16 light-years, it's the nearest of this group of stars. Altair is one and a half times larger than the Sun and ten times as luminous. Intriguingly, Altair rotates on its axis once every six and a half hours (compare this with the Sun, which rotates once every 25 days). Because of this rapid rotation Altair, as seen from a hypothetical planet in orbit about the star, would look like a flattened sphere.

If your sky is free of city light pollution, you should also be able to make out the Milky Way, paralleling the horizon northeast to southeast forming a kind of dusty 'backdrop' to the incredible summer stars.

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