Skywatch for the week of January 4, 2021
Mon Jan 4, 2021 PERIHELION
The earth's orbit is slightly elliptical, so its distance from the sun changes through the year. The earth reached perihelion at 3 a.m. on January 5th. Perihelion is the point in its orbit when earth is closest to the sun. On average, we're about 93 million miles from the sun, but right now, we are just a little under 91 and a half million miles from it. So if we're a million and a half miles closer to the sun, how come we're having winter? Well, not everyone on earth is having winter; summer has just begun for folks who live below the equator. Our seasons are not caused by our slight variation in distance, but by the 23 and a half degree tilt of our planet as it orbits. The rotating, revolving earth is like a gyro2-scope, with the north axis aimed nearly at Polaris, the North Star. Now our north hemisphere is tipped away from the sun; this puts the sun lower in our sky, and with less direct sunlight we get cooler temperatures.
Tue Jan 5,2021 RIDDLES IN THE DARK
J.R.R. Tolkien was born on January 3rd, 1892. In his fantasy story, “The Hobbit,” the hero Bilbo meets a strange creature named Smeagol down in a deep cave, and the two play a game called, “riddles in the dark.” One of the riddles is this: “It cannot be seen, cannot be felt Cannot be heard, cannot be smelt. It lies behind stars and under hills And empty holes it fills.” And the answer is, “darkness.” Now, here’s an astronomy riddle I made up: “At weddings they appear; and at front doors it’s them we hear. They’re found on Elven hands and soda cans; ‘Round Saturn they appear.” And the answer is, “rings.” Let’s try another astronomy riddle. “It’s always on, and never off. It’s more when nearby, and less when far off; It keeps the sun from spilling out. And in the end, it stops us going up and about.” The answer is “gravity.” If you want to hear these riddles again, go to WQCS dot org, and you’ll find this podcast and a transcript.
Wed Jan 6, 2021 ROBERT FROST AND CANIS MAJOR
The American poet Robert Frost was a keen observer of the world and nature. In his writing, Frost often captures the simple majesty of the Universe. You notice it in his poem, the Star Splitter, in which he begins by telling us, “You know Orion always comes up sideways,” as indeed he does, first the forward shoulder and leg, then the hunter’s belt, and lastly the trailing shoulder and knee. Orion now holds a prominent place in the southeast sky after sunset. If you trace the stars of his belt downward, you will find the star Sirius in the constellation of the Big Dog, Canis Major, and Frost wrote a poem about this heavenly hound as well. Frost places Sirius in the dog’s eye when he says: “The great Overdog That heavenly beast With a star in one eye Gives a leap in the east. He dances upright All the way to the west And never once drops On his forefeet to rest.” Because of the earth’s rotation, Canis Major does move across the sky just the way Frost describes it.
Thu Jan 7, 2021 CALENDAR ORIGINS
Our calendar is based on patterns in the heavens – the earth’s rotation, the phases of the moon, the orbit of the earth about the sun. Our calendar has its origins thousands of years ago, from Egypt. By keeping close watch on the sun’s progress through the sky, ancient Egyptians were able to accurately measure the length of the year, and knew it was about 365 and a quarter days long. Their calendar had 12 months of 30 days each, which worked out to 360 days total. Then they had five extra days or “empty” days, known as heiru renpet, which they used as a holiday at the end of the year. The new year began with the predawn rising of a star they named Sothis, which appeared in the east just before sunrise. This happened in July, around the time each year when the Nile River flooded. Sothis is still shining up there; we call it Sirius, the dog star, the brightest star in the night, which appears below and to the left of the constellation Orion, in the southern sky these early winter evenings.
Fri Jan 8,2021 JOHANNE BODE AND BODE’S LAW
Johanne Bode was born on January 19, 1747. In 1772 he advanced a mathematical theory which suggested the presence of additional planets, beyond the seven that were known of at that time. Start at zero, then skip to 3, then 6, and now keep on doubling the number. Then add 4 to each of those numbers and finally, divide by ten, giving you .4, .7, 1, 1.6, 2.4, 4.8, and 9.6. Those are roughly the spacings between the planets, expressed as astronomical units, the average earth-sun distance. This theory, called Bode’s Law, is quasi-scientific. It doesn’t work every time, and it’s not particularly exact, but it did point to a gap between the orbits of Mars and Jupiter. Astronomers began the search for the proposed missing planet, and on January 1st, 1801, the Sicilian astronomer Father Giuseppe Piazzi used a telescope to discover 500 mile-wide Ceres, the largest rock in the asteroid belt.