Skywatch for the week of May 17, 2021
Mon May 17, 2021 NOVAE AND SUPERNOVAE
Supernovas are exploding stars. The last nearby supernova seen with the naked eye occurred in the Large Magellanic Cloud, 160,000 LY away, in 1987. But a simple nova, while it represents a dying star, is not an exploding star. Novae are found in binary systems, where one star is still on the main sequence and the other has become a white dwarf. The white dwarf’s gravity is sufficient to pull gas off its companion, but the stolen gas doesn’t go straight onto the dwarf; instead, it spirals around, forming an accretion disc that surrounds the dying star. At regular intervals of time, this disc gas touches down on the surface of the white dwarf and ignites, creating a flare-up in the star. The white dwarf brightens considerably for a while, then dims down again – until more gas has piled up in the disc and the cycle repeats itself. This can go on for years and years. However, if the white dwarf pulls too much material down and its end mass becomes great enough, it can also explode and become a supernova!
Tue May 18, 2021 WAUPEE AND SHENANDOAH
The bright star Arcturus which we see in the eastern evening sky was known to the Algonquin Indians as Waupee, or the White Hawk. One day, in a clearing in a great forest, Waupee heard the faint sound of music from the sky. He looked up and saw, much to his surprise, a magical basket descending from above. In the basket were 12 sisters. When the basket reached earth the heavenly sisters leaped out, and linking hands, began to dance in a circle. White Hawk fell in love with the youngest sister and they became husband and wife. But she was Shenandoah, which means "daughter of the stars." And she longed to return to her father in the sky. The day came when Waupee and Shenandoah took their young son up into the sky country, where they became white hawks. And nearby Arcturus you may still see the sisters’ magic basket, a faint circlet of stars which forms the constellation of the Northern Crown - Corona Borealis.
Wed May 19, 2021 HOWLING COYOTE
An old Navajo story tells how the stars came to be. Long ago, it’s said, there were no stars, and in the dark of night the people lost their way. So the Great Spirit sent all of the animals down to the river, and had them gather up the bright shining stones in the stream bed. They carried those stones up into the sky where they became stars. Great Spirit told the animals to put them in patterns which would show the people which animals had set those stars in place. Now the small animals could not carry many stars and Great Spirit asked Coyote to take a bag of stones to help them complete their pictures. But Coyote soon grew tired of his task, and he flung his bag of stones across the sky, scattering them, and making a jumble of the pictures. Then Coyote was sorry, not because he had made it hard to see the constellations, but because he had forgotten to put his own picture up in the heavens. And that, say the Navajo, is why the Coyote howls at night.
Thu May 20, 2021 THE SUN AND THE SOLAR YEAR
The sun is on the move. Now this movement is much more subtle than the obvious sunrise-sunset stuff we get every day, due to earth’s rotation. If you could make the sun dimmer so that you could see it and stars at the same time, (something that only happens in a planetarium or during a total solar eclipse!) you’d notice the sun drifts eastward against the background of stars. It’s a very slow motion caused not by earth’s rotation, but by its revolution about the sun, which displaces the sun’s position by about 1 degree of angle a day – that’s less than the width of your little finger at arm’s length! After roughly 365 days, the sun returns to where it had been exactly a year ago. Right now the sun appears very close to the Pleiades, or Seven Sisters star cluster in the constellation Taurus. Next May 20th, the sun will be alongside the Pleiades again. This defines the solar year as the amount of time needed for the sun to go full circle, once around the zodiac in the heavens.
Fri May 21, 2021 ARTHUR CONAN DOYLE
Sir Arthur Conan Doyle was born on May 22nd, 1859. He was, of course, the creator of the fictional detective Sherlock Holmes, one of my favorites. It bothers, me, though, that Holmes didn’t know anything about astronomy, nor did he care. When Dr. Watson informed him, for instance, that the earth orbited the sun, he replied, “What… is it to me? You say we go round the sun. If we went round the moon it would not make a pennyworth of difference to me or my work.” But I think that if Holmes gave astronomy a chance, it would appeal to his powers of observation, and of his deductive and inductive reasoning. Through induction, Holmes could infer that if we live on a planet, one of many, that goes round the sun, then it would be logical to assume that there were other planets out there, going round other suns. And he did say, “When you have excluded the impossible, whatever remains, however improbable, must be the truth.” Sounds a lot like black holes to me!