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The Sky This Week, 2020 March 17 - 24

Spring has sprung!
Orion, imaged 2011 December 31 from Morattico, Virginia.
Orion Orion, imaged 2011 December 31 from Morattico, Virginia
with a Canon EOS Rebel T2i DSLR

The Moon graces the pre-dawn sky this week, scudding along the southern reaches of the ecliptic as she wanes through her crescent phases.  New Moon occurs on the 24t at 5:28 pm Eastern Daylight Time.  If you get up early in the morning of the 18th, find a spot with a good view to the southeast and you will be rewarded with a beautiful grouping of the Moon, Mars, and Jupiter forming aa tight triangle just over two degrees across.  On the following morning Luna may be found several degrees to the southeast of Saturn.

The Globe at Night citizen-science program campaign for March is underway and running through the coming week.  The featured constellation is Orion, which should be visible to almost anyone under any sky.  Think of this as an opportunity to introduce your home-bound kids to astronomy and the concept of scientific observation.  The procedure is simple.  Locate Orion in the sky; he is prominently placed just west of the meridian at the end of evening twilight.  Open the Globe at Night web app and compare your view with the various star charts on the page, then fill out the observation form.  Your observations will be compared to those compiled in 2011 and 2012 to determine the effects of new LED street lighting programs that are replacing older technologies.  You are encouraged to make multiple observations since local weather conditions may impact your nightly views.  I also encourage all to support the program throughout the year.  “Sky awareness” is the first step to the rewarding experience of amateur astronomy. 

The vernal equinox occurs on the 19th at 11:50 pm EDT.  This moment marks the instant when the ecliptic longitude of the Sun reaches zero degrees and begins another circuit around the sky.  This is the earliest occurrence of the equinox since the year 1896, and we will continue to see equinoxes on the 19th (in EDT) every four years through the year 2096.  We then have a 40 year period before the equinox once again starts a four-year cycle of falling on the 19th.  So why does this happen at all?  We can blame the calendar and the leap-year cycle.  The explanation is rather lengthy, but suffice it to say that or Gregorian Calendar system will keep the equinox occurring close to the astronomical equinox for quite a while to come.  We probably won’t accumulate a full day’s error until somewhere around the year 5000!

Many people think that the date of the equinox is when we also have equal lengths of day and night, but this is not the case.  On the 19th the length of daylight is four minutes longer than that of night.  This is due to the effects of atmospheric refraction and the apparent diameter of the Sun’s disc.  Sunrise occurs when the first visible portion of Old Sol’s limb crests the horizon in the morning and sunset occurs when the last sliver disappears at sunset.  By these criteria the actual day of “equilux” occurred on March 16th.  From now until the next “equilux” day on September 25th we will have more daylight than darkness.

Bright Venus continues to dazzle in the early evening hours.  She is rapidly moving northeastward along the ecliptic and now stands prominently above the western horizon.  As bright as she is, she won’t reach her peak brilliance until late April, but if you find yourself in a dark-sky location try to look for shadows cast by our sister planet.  Use a white shirt or a piece of paper for this interesting experiment.

Mars, Jupiter, and Saturn may be found low in the southeastern sky before dawn.  Mars is the faintest of the three, but you should easily be able to identify him by his reddish tint and rapid motion.  On the 18th the waning crescent Moon passes just to the south of Mars and Jupiter, and on the morning of the 20th Mars passes just under a degree south of Old Jove.  Mars then draws a bead on Saturn, and the red planet will pass Saturn on the morning of the 31st.