Skywatch for the week of June 17, 2019

Tue June 18, 2019 STAR CHARTS Computers, laptops, tablets, ipods, ipads and smartphones can all provide electronic star charts to anyone who wants to look up and learn about the stars. Being old-fashioned, I still find myself most comfortable looking at star charts that are drawn on paper, with black dots on a white background, which provides the best contrast. Both electronic charts and paper charts show the bright stars as big dots and the fainter stars as smaller dots. Star charts are filled with all kinds of cryptic writing: the brightest stars have Arabic, Greek or Latin names written beside them. We can also use the Greek alphabet as well as the Roman alphabet to designate stars from bright to dim: Spica is the brightest star in Virgo and so is designated as Alpha Virginis. The next brightest star, Zavijava, is Beta Virginis, and so on down until you run out of letters. And for the past few hundred years, Flamsteed numbers have been used, as we catalog the stars numerically in each constellation from west to east.

Wed June 19, 2019 THE BRIGHTEST STARS ARE RAREST When you look at the sky this evening, you first thing you notice are the bright stars. These 1st magnitude stars, like the blue giant star Spica in the constellation Virgo, and the red giant star Arcturus in the constellation Bootes, or other giant stars such as Sirius and Procyon, in the Big and Little Dogs, or Castor and Pollux in Gemini, are scattered about the sky, and it would seem that these giant stars are fairly common. But the giant stars are actually quite rare. The most common of stars in our galaxy are red dwarfs, and because they’re so small and cool, they’re not visible to the unaided human eye. Barnard’s Star, which rises out of the east in mid-evening, is a typical red dwarf. But unless you have a pretty good telescope and know just exactly where to look for it, you’ll never see Barnard’s Star, which is just under six light years, or 35 trillion miles away, almost a next-door neighbor, cosmically speaking.

Thu June 20, 2019 ANCIENT SUN TEMPLES Stonehenge was built over forty centuries ago; it’s one of over a thousand circles of standing stones that can be found throughout the British Isles and Europe. On the first day of summer, the sun rises over an outlying heelstone, as viewed through a central arch of stones. Other old observatories around the world mark the sun’s seasonal positions. In ancient Egypt, temples were built so that at the summer solstice, the sun’s rays shone through tall columns to sanctuaries within. At the Bighorn medicine wheel in Wyoming, piles of carefully placed stones pointed toward the summer sunrise. For hundreds of years in New Mexico, a slender ray of sunlight – the sun dagger of the Anasazi – sliced through a petroglyph spiral on the first day of summer. And there is the Sun Temple, built by the Incas at Machu Pichu – but of course Peru is south of the equator, and now it is the winter solstice sun that is framed in this ancient observatory’s window.

Fri June 21, 2019 FIRST DAY OF SUMMER Summer officially begins today at 1:54 p.m., Eastern Daylight Savings time. It’s at this precise time that the sun can be found shining directly overhead at local noon, not here in Florida, but as seen from a point on the Tropic of Cancer at twenty-three and a half degrees North latitude, about in the middle of the Carribean. When it is local noon here, the sun will be as high in the sky as possible for our latitude. We’re at 27½ degrees North here, so at midday the sun will be about 4 degrees south of our zenith. Today is called the summer solstice, as the sun stops its northerly progression; sol stice – sun stop. It also marks the longest period of daylight and the shortest period of night in the year, at least in Earth’s northern hemisphere. In the southern hemisphere, winter has begun. For the next six months the sun’s altitude at noon will drop and then we’ll be at the winter solstice.