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The Sky This Week, 2018 March 27 - April 3

Moons and calendars
The Moon rising over a formation in the Garden of the Gods, Colorado Springs, Colorado
The Moon rising over a sandstone formation, Garden of the Gods, Colorado Springs, CO on 2013 March 23,
imaged with a Canon EOS Rebel T2i DSLR, 250mm @ f/1, 1/320s, ISO 200.

The Moon brightens the overnight hours as she descends the ecliptic and courses through the sparse star fields of spring.  The second Full Moon of March occurs on the 31st at 8:37 am Eastern Daylight Time.  This being the second Full Moon of the month it is often referred to as a “Blue Moon”.  Generally Blue Moons occur at intervals of about 2 years 8 months, but 2018 is unusual in having Blue Moons in both January and March.  The next one will fall on Halloween, 2020.  The next time we have two Blue Moons in the same year won’t be until the year 2037.

In addition to the name “Blue Moon”, this particular Full Moon is also known as the “Paschal Moon”.  Since it is the first Full Moon to fall after the vernal equinox, it sets the date of Easter in the Christian faith.  In Judaism, which observes a lunar calendar, the observation of Passover begins on the 15th day of the month of Nisan, which also corresponds to the appearance of the first Full Moon following the equinox.  For the most part Easter and Passover occur at the same time, but there are exceptions in the way lunar months are counted in the Hebrew Calendar.  Since a “lunar month” is about 29.5 days, 12 such months yield a year of 354 days.  The eleven extra days in the solar calendar are made up by the periodic insertion of an extra month in the calendar.  Extra months are added at intervals of from 2 to three years, depending on where the year falls in the 19-year Metonic Cycle.  Over the course of this cycle there are 12 years of 12 months and 7 years of 13 months.

The bright Moon wipes out the view of many of the springtime stars.  You can still enjoy the departing winter stars that surround Orion, but you’ll need to do this early in the evening since the westernmost stars of the Great Winter Circle now set by midnight.  There are a few bright stars to enjoy in the spring sky, though.  Regulus, the heart of Leo, the Lion, is flanked by the Moon on the evenings of the 27th and 28th.  Luna perches about just over seven degrees above Spica, the brightest star of the sprawling but faint constellation of Virgo.  The brightest star in the northern sky, Arcturus, shines brightly in the east as the night passes, climbing to a place of prominence in the early morning hours.  By midnight, look just to the north of the zenith to see the seven second-magnitude stars that make up the “Big Dipper” asterism.

Venus and Mercury gave us a really good show over the past couple of weeks, but this week Venus has lost her planetary companion to the encroaching Sun.  In just two short weeks Mercury has gone from greatest eastern elongation, when he was easily visible to the naked eye, to conjunction with the Sun, when the fleet planet passes between Earth and Old Sol and is invisible.  Venus, however, continues to climb higher into the evening sky and becomes more obvious in the west with each passing evening.  By the end of the week she sets just after the end of evening twilight.  Her journey through the sky is a lonely one.  She’s moving through the constellations of the late autumn sky and won’t encounter any bright objects until she drifts between the Pleiades and the bright star Aldebaran in late April and early May.

You should be able to spot bright Jupiter low in the southeastern sky during the late evening hours.  He now rises just before 11:00 pm and should be high enough to train the telescope toward by 1:00 am.  You’d probably want to wait until the pre-dawn hours to view him, though, since he’ll be joined by ruddy Mars and ringed Saturn.  The latter two steal the show this week, as Mars passes the more distant Saturn on the morning of April 2nd.  At this time the two planets will be just over one degree apart.  If you have a pair of binoculars and are up well before the Sun look just below and to the right of Mars.  If you see a fuzzy glow of light you’ve found Messier 22, one of the brightest globular star clusters the galaxy. 

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