AstroCal for March 2021
We start this month with the planets visible in the morning sky. Mercury, Jupiter, and Saturn can be seen low in the ESE forty minutes before sunrise. Mercury will drop lower each day and be lost in the Sun’s glare by mid-month. The two Gas Giants will climb higher each day. Since their historic close encounter on December 21, 2020, they have continued to drift apart. The gap between them will increase from 8.2 degrees on Mar 1 to 11.8 degrees on Mar 31. They will continue distancing themselves from each other until 2030 when they will appear on opposite sides of the sky.
Mars can be found high in the west all month long. It will pass 3 degrees south of The Pleiades star cluster on Mar 4 and 7 degrees of the star Aldebaran in Taurus the Bull on Mar 20.
Mars continues to put more distance between itself and the Earth, starting the month 1.48 astronomical units (AU) away, increasing to 1.72 AU by the end of the month. An AU is a short-hand way of expressing the vast distances between objects in the Solar System. One AU equals the average distance between the centers of the Earth and Sun (93 million miles). This translates to the Earth-Mars distances on Mar 1 as 137 million miles and Mar 31 as 160 million miles. This month’s viewing challenge involves Uranus: using binoculars or a small telescope, it can be seen 20 degrees to the lower right of Mars in early March. The gap will grow to 35 degrees by the end of the month. Venus will not be visible this month as it passes 1.3 degrees south of the Sun on March 26 during a period called superior conjunction.
A handy guide to measuring astronomical degrees can be found at arm’s length: One finger held up at arm’s length covers about one degree. Three fingers resembling the Boy Scout salute equals 5 degrees. A closed fist covers about 10 degrees from thumb to little finger. The Texas ‘hook ‘em horns’ salute is typically 15 degrees and the ‘surfer’ greeting with only the thumb and pinky finger extended outward from a closed fist measures about 25 degrees.
Clear March nights will offer stunning views of Orion the Hunter including the bright blue star Rigel marking his knee and giant red Betelgeuse in his shoulder. Following the three stars of Orion’s Belt to the left, one will easily spot the brightest star we can see in the northern hemisphere: Sirius the Dog Star located in Canis Major, the Big Dog. Rigel and Betelgeuse are also two of the top five brightest stars seen in this hemisphere. Following the Belt in the opposite direction will point your eyes to The Pleiades star cluster in Taurus the Bull.
During the first two weeks of March, it may be possible to see Zodiacal Light in the west just after the end of evening twilight. The Zodiacal Light is a faint glow of interplanetary dust along the ecliptic plane of the solar system. Picture the planets sitting on a large plate with the Sun at the center – the plate itself would represent the ecliptic plane.
With the Full Moon occuring at 2:48 p.m. EST on Sunday Mar 28, the final week of the month will be bright enough for snowshoeing and cross country skiing as long as the snow cover lasts. Other notable Lunar events include the New Moon on Mar 13, the First Crescent on Mar 14 (always a viewing challenge low in the western sky right after sunset), the First Quarter Mar 21.
The Vernal Equinox marking the first official day of spring takes place on March 20 at 5:37 a.m. EDT. (Note the transition from EST to EDT – Daylight Saving Time begins at 2:00 a.m. on March 14 this year and ends on November 7). The Equinox occurs when the vertical ray of the sun (the point where the sun would appear straight over head) crosses the Earth’s Equator. The Earth’s axis tilts 23.5 degrees from the aforementioned elliptical plane of the Solar System. In the higher latitudes, this results in the changes that occur in the length of night and daylight hours over the course of the year. At the Equator, there is always 12 hours of daylight and 12 hours of darkness. The Equinox (both spring and fall) are the only times of the year when there is ‘equal night’ (and daylight) everywhere on the planet. By the Summer Solstice on June 20, 2021, the northern parts of the United States will be experiencing 17 hours of daylight and only 7 hours of darkness. The North and South Poles, by contrast, swing from 0 hours of daylight to 24 hours between June 20 and December 21 each year.
Compiled by Ken Raisanen of WOAS-FM – information provided by Abrams Planetarium Sky Calendar, Michigan State University. More information can be found on the their website at http://abramsplanetarium.org/ or on Twitter at http://twitter.com/AbramsSkyNotes