Skywatch for the week of June 15, 2020

Tue June 16, 2020 THE BRIGHTEST STARS ARE RAREST When you look at the sky this evening, the first thing you notice are the bright stars, called first magnitude stars since they’re the brightest. These 1st magnitude stars, like the blue giant star Spica in the constellation Virgo, and the red giant star Arcturus in the constellation Boötes, 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.

Wed June 17, 2020 WILLIAM PARSONS, LEVIATHAN BUILDER 220 years ago today, Sir William Parsons was born - June 17th, 1800. Forty years later, he built the Irish Leviathan. At sixteen tons, and with a primary mirror six feet across, the Leviathan would remain the world’s largest telescope for the next seventy years. It was so big that it couldn’t be rotated, so by leaning the instrument east to west, Parsons could observe objects for over a half hour. The Irish Leviathan was so powerful that he could actually see individual stars in distant galaxies like M51, the Whirlpool, roughly 40 million light years away! A lot of the colorful descriptive names of nebulas and galaxies were made up by Parsons – the whirlpool galaxy, the crab nebula, the Saturn nebula. After Parsons died, his son continued his work, but his grandson had no interest in astronomy, and Leviathan was dismantled, its metal supports melted down for ammunition during the First World War. But it was rebuilt in 1999.

Thu June 18, 2020 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 19, 2020 FIRST DAY OF SUMMER Summer officially begins tomorrow, Saturday, June 20th, at 5:43 pm, 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, out in the middle of the Pacific Ocean. When it’s 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. But for those of us in the US, for the next six months the sun’s altitude at noon will drop and then we’ll be at the winter solstice.