A thin crescent moon will put on quite a display this weekend. Start looking about 40 minutes after sunset in the west-northwest -- and bring binoculars for the best show.


 

A thin crescent moon will put on quite a display this weekend. Start looking about 40 minutes after sunset in the west-northwest -- and bring binoculars for the best show.

Saturday night, April 25, the moon will be very thin and difficult to see, low to the horizon in the glare of dusk. The next night, Sunday, the moon will have moved up and to the left, a bit thicker and much easier to see. Sunday night, the moon’s sliver will stand above Mercury. Right between them will be the wonderful Pleiades star cluster.

Keep watching night to night as the crescent moon thickens, heading for first-quarter phase on May 1. That’s when the moon looks half lit -- when it is a quarter way around Earth in its monthly orbit.

So when is it a quarter lit? That’s when the crescent is about halfway to first-quarter!

Sighting of the elusive, ultra-thin crescent when it is only 24 hours or less after “new” phase is somewhat of a sport among observers. New moon actually occurs on Friday, April 24, at 11:23 p.m. EDT. When you see it after sunset Saturday, if you are in the Eastern Time zone, the moon’s crescent phase will be only about 21 hours old, or if you live on the West Coast, 24 hours old. The record early sighting by unaided eyes is 15.5 hours from new moon.

The moon is completely “new” only during a solar eclipse, when the darkened side of the moon is fully facing us, between Earth and the sun. Most months, the moon slides just below or above the sun.  Although we cannot expect to see it, the moon actually sports a “hairline” crescent of light at these passages.

Be sure to see Mercury in the western twilight this week. This is the best opportunity this year to see the planet in the evening sky. Never far from the sun, you have the best chance to see Mercury when the ecliptic is standing high up in respect to the horizon.

As you may recall, the ecliptic is the imagined line encircling the heavens where the sun appears to travel and the moon and most of the planets obediently and closely follow. The moon and majority of planets never stray more than 8 degrees from the ecliptic line, one way or another, because they all follow almost the same flat plane. Picture the solar system as a music CD (I used to say phonograph record, but that is so ’70s). Place a marble, or your fingertip, in the center hole of the CD, representing the sun. This is also a way to imagine a spiral galaxy such as the Milky Way Galaxy in which we live.

Mercury, the first planet out from the sun, glows at magnitude -0.5 and may appear yellow or orange, due to being low in the sky. As the sky darkens, watch for the glittering Pleiades come into view; get an early view with binoculars before you can see them with unaided eyes. Each night, the Pleiades will shift a little closer to the planet.

Try and appreciate the practically unfathomable differences in the distance of these celestial places. The moon is on average 238,000 miles away. Mercury is as close as about 60 million miles and as far as around 130 million miles. The Pleiades are roughly 425 light years from Earth, or 2.4 quadrillion miles!

Those of us who get up before dawn (let me know what you see) and have the benefit of a low eastern horizon (unlike me, which is one reason I’m usually still in bed), will be able to enjoy the gloriously bright planet Venus, magnitude -4.7. We enjoyed Venus dominating the western sky for the last several months; now it is on the flip side. Much higher and far to the right stands brilliant Jupiter (magnitude -2.2). Mars is presently to the lower right of Venus and very hard to see in the bright light of dawn.

Saturn is easy to see in the evening, high in the south around 9 p.m.

Mercury, however, is often missed due to its nearness to the sun and hills or trees that frequently block our normal vantage point. Sightings of Mercury played an important role in proving Einstein’s General Theory of Relativity, published in 1915. In part, Relativity showed that a gravitational field will bend light. Observed positions of Mercury were slightly off of prediction due to the reflection of sunlight off of Mercury bending past the sun.

Your reports, comments and questions may be sent to me at pbecker@wayneindependent.com or Peter Becker c/o The Wayne Independent, P.O. Box 122, Honesdale, PA 18431.

Keep looking up!