The Transylvania Times -

Mountain Skies: Vernal Equinox Occurs Wednesday Evening

 

March 18, 2019



The Sun

The first day of spring is marked by the vernal or spring equinox, the moment in time when the sun, in its apparent path around the sky, crosses the celestial equator on its way North for the spring and summer. This year the equinox occurs at 5:58 p.m. EDT, Wednesday, March 20.

The Planets

As expected, Mercury has once again disappeared from viewing by even the most dedicated observer. It passed by the sun in inferior conjunction last Thursday (Eastern Daylight Time). The passing of this elusive planet by the sun generally can’t be observed in the glare of the sun. However, some may recall that on May 9, 2016, we watched (in and out of clouds from Brevard) as Mercury passed directly in front of the sun and, with properly filtered telescopes, we were able to watch it cross the disk of the sun. Mercury moves quickly since it is the closest planet to the sun; it must, or the sun’s gravity will pull it in to a spectacular demise. Since it moves so fast, it will circle the sun roughly three times each year from our perspective. It has now left the evening skies and will soon show itself in the predawn twilight late this month. By June it will be back in the evening sky, pass by the sun on July 21 and, for a third time this year on Nov. 11. But that one will be different. On Nov. 11, the geometry of the planets will be such that Mercury won’t just simply pass by the sun; it will pass in front of the sun. In other words, we will have a transit of Mercury visible in total from the Carolinas. Mark your calendars! It won’t be as spectacular as the Great American Eclipse of August 2017 since Mercury is a mere speck compared to the moon, but it will be fun to observe.

This month we can still spot Mars, slowly sinking into the southwest evening twilight and setting before midnight. A couple of hours later the other major planets begin to appear with Jupiter rising shortly after midnight, Saturn following by about two hours, and the brilliant Venus still rising before sunrise. By the time morning twilight sets in, these three form a line in the southeast tracing out the plane of the solar system. This line continues to shift each morning as the planets have their own motions against the background constellations and the whole sky moves one degree per day due to the earth’s motion around the sun. But basically, Jupiter and Saturn rise about four minutes earlier each morning while Venus sinks into the dawn.

The Stars

While the bright stars of winter continue to dominate the southern sky in the early evening, turn around and look to the North, specifically the northeast. Here, low in the sky, we find the familiar pattern of the Big Dipper. It’s still not late enough in the year to see it high in the North, but we can see it rising, standing on its handle with the bowl opening to the left. Watch the Big Dipper over the next several weeks as it gets higher and higher in the northeast until, with the coming of spring, it will lie high in the North. Realize, of course, that the Big Dipper is not an official constellation as defined by the International Astronomical Union. Astronomers would call it an asterism, a pattern of stars that is recognizable but not one of the 88 official constellations. Where we see the familiar dipper, the ancient Greeks saw the long tail of the Great Bear, Ursa Major.

Now use the two stars in the end of the bowl of the Big Dipper to find the most famous star in the sky. Draw a line between the two stars in the bowl and trace it to the left about five times the distance between the two stars and you will come to a bright (but not the brightest) star. This is Polaris, the North Star. The North Star is the end of the tail of the Little or Lesser Bear, Ursa Minor. To our way of thinking, it is also the end of the handle of the asterism we call the Little Dipper. Once you have found the North Star, look down to the right to locate two moderately bright stars. These are the so-called “Guardians” which mark the end of the bowl of the Little Dipper. The other stars of the Little Dipper, stretching between the Guardians and the North Star, are much fainter; you must have a very clear, dark night to spot them and, thus, trace out the entire Little Dipper.

Celestial Calendar

•March 20, 5:58 p.m. EDT - Vernal equinox. Spring begins.

•March 20, 9:43 p.m. EDT - Full moon.

•March 28, 12:10 a.m. EDT - Last quarter moon.

•April 5, 4:50 a.m. EDT New moon.

(About the Learning Center at PARI: The Learning Center at PARI is a public not-for-profit 501 (c) (3) organization established in 1998. Located in the Pisgah National Forest, the Learning Center provides STEM educational programs at all levels, from K-12 through post-graduate research. For more information about the Learning Center at PARI and its programs, visit http://www.pari.edu.)

 
 

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