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Author Fred Schaaf describes a very thin crescent moon in his book The 50 Best Sights in Astronomy and How to See Them

Recounting an early sighting of a very young moon, he writes that the moon was “thin as a single snippet of pale gold hair falling, falling gently through dusk to the repose of the low forest horizon,” and that it was “a slight but dreaming and luminous smile scarcely touching the face of that twilight sky, a face whose tender tones and shades were the only things which could possibly be delicate enough to hold the moon. … An indelible mark, a slenderest sliver of pure celestial beauty that eternity keeps forever from harm or slightest alteration.”

Here in the Coachella Valley and elsewhere in the U.S., there will be yet another rare chance to see not just one, but two unusually thin crescent moons, about 36 hours apart, on two consecutive days: at dawn on Friday, Feb. 28, and at dusk on Saturday, March 1. Binoculars will be a great help on both occasions. The astronomical new moon, invisible as it passes a few degrees north of the sun, occurs almost midway between the two sightings, at 12 a.m. (midnight) at the beginning of March 1.

Illustrations of the old crescent at dawn on Feb. 28, and of the young crescent at dusk on March 1, appear on the February 2014 Sky Calendar, available online at www.pa.msu.edu/abrams/skycalendar.

Valley residents can try for the old crescent on Friday, Feb. 28, between 5:46 a.m. and 5:56 a.m., when the very thin crescent will appear 11 to 12 degrees south of due east, rising slowly, from 2 degrees to 4 degrees above the horizon. That “viewing window” spans only from 30 minutes to 20 minutes before sunrise, so binoculars are recommended in the brightening twilight.

Planets might be helpful for locating the moon that morning. Venus will be very prominent, some 22 degrees up in the southeast, with fainter Mercury 22 to 23 degrees to the lower left of Venus. The moon can be found 12 degrees lower left of Mercury.

The young moon on Saturday, March 1, will best be seen in the Coachella Valley between 6:03 p.m. and 6:13 p.m., with the hairline thread of a crescent appearing from 4 degrees to 3 degrees south of due west, and sinking slowly, from 5 degrees to 3 degrees above the horizon. This viewing window spans from 20 to 30 minutes after sunset, so binoculars are again recommended for spotting the young crescent, which will be even thinner and closer to the sun than the old crescent of the morning before.

Seeing either one of these two crescent moons will require clear weather, and careful advance planning to make sure the line of sight from observer to moon will not be obstructed by local topography; after all, there are plenty of mountains around here which often block the view of events such as these!

From the Coachella Valley, different sites may well be required for the two sightings. You can increase your chances by checking out your viewing site in advance, by observing the moon at a date and time when it will have nearly the same position in the sky as the moon at the target date and time.

Here are directions for accurately predicting the positions of both the old and the young crescent moons at the middle time of each recommended 10-minute window.

The old moon (at dawn, 5:51 a.m., Friday, Feb. 28): Observe the waning gibbous moon on the evening of Monday, Feb. 17, at 8:38:15 p.m. (It will be 91 percent full and easy to observe if not hidden by clouds or local topography.) You will find it at azimuth 97.3 degrees (7.3 degrees south of due east) and altitude 3 degrees. When you look for the moon on Feb. 28 at 5:51 a.m., you’ll find it 4.3 degrees to the right of the spot where the moon appeared on Feb. 17 at 8:38:15 p.m.

For an even closer forecast of position, observe the 84 percent moon the next evening, Tuesday, Feb. 18, at 9:35:30 p.m., and you’ll find it at azimuth 102.3 degrees (12.3 degrees south of east), and altitude 3 degrees. Then when you look for the moon on Feb. 28 at 5:51 a.m., you’ll find it just 0.7 of a degree to the left of your Feb. 18 sighting.

The young moon (at dusk, 6:08 p.m., Saturday, March 1): Observe the 94 percent moon on the morning of Tuesday, Feb. 17, at 7:18:40 a.m. You’ll find it then at azimuth 264.7 degrees (5.3 degrees south of west), altitude 4 degrees. Then, to find the young moon on March 1, look just 1.7 degrees to the right of where you spotted the moon on Feb. 17.

What to look for when you observe a thin crescent moon: Can you see any illumination of the moon’s dark side? It’s called earthshine for a good reason: It is the moon being illuminated by sunlight reflected by the Earth. Usually, earthshine is not seen when the lunar crescent is very close to the sun, because the moon is immersed in the foreground bright twilight sky. For your best chance to detect earthshine on a very thin crescent, look soon after moonrise, before the sky gets too bright, or not long before moonset, when the sky has darkened sufficiently. But if the moon is very low, then Earth’s atmosphere will dim the light.

When you observe a very thin lunar crescent, note how much of the moon’s circumference you can see. It will help to visualize the moon’s disk as a clock face. When the crescent isn’t too close to the sun, an arc of 180 degrees is typical. But the arc of a crescent moon very close to the sun is noticeably shorter.

For example, on the morning of Feb. 28, if you perceive the moon’s circumference illuminated from 4 o’clock to 10 o’clock, then the sunlit arc would extend halfway around the clock face, and its length would be 180 degrees. But if you observe the sunlit arc only from 4 o’clock to 9 o’clock, then its length would be just 150 degrees.

Are there any breaks in the crescent, or any thin spots where only a thread of light makes the crescent continuous?

Note the times of your first and last observation of the crescent. Calculate the time interval between your sightings and new moon, which occurs at 12 a.m. at the beginning of March 1.

Alexander Seidler and I spotted opposing crescent moons on consecutive days, on Dec. 31, 2013, in morning twilight (an easy sighting for binoculars and unaided eye within 21 hours before new), and on Jan. 1, 2014 very early in evening twilight (a very difficult sighting, within 14 hours after new). Alex had not previously observed a crescent moon within 24 hours of new, and I had never before spotted opposing crescents on consecutive days. Read more about our sightings here.

From the Coachella Valley, the opposing pair of Feb. 28 and March 1 will be more balanced, with both crescents just more than 18 hours away from new. The morning crescent, though farther from the sun, will be less favorable for viewing, rising only 42 minutes before the sun, compared to the evening crescent setting 48 minutes after the sun.

Published in Astronomy

February 2014 at dusk: The two brightest “stars” at dusk in February are, by a wide margin, steady yellowish Jupiter, high in the east, and blue-white, madly twinkling Sirius, the dog star, in the southeast. The only other evening planet is Mercury, very low south of west, but it will fade and is on its way to conjunction with the sun.

The waxing gibbous moon, four days before full, appears near Jupiter on the evening of Feb. 10.

Surrounding Jupiter is the huge Winter Hexagon of Sirius-Procyon-Pollux-Capella-Aldebaran-Rigel. The noticeably red star Betelgeuse is also within the hexagon. Find the three-star belt of Orion, the hunter, midway between Betelgeuse and bluish Rigel. The belt, extended southeastward, locates Sirius. Extend the belt in the opposite direction, and turn north a bit, and you’ll find Aldebaran, eye of Taurus, the bull. Go farther to find the Pleiades, or seven sisters—a wonderful sight for binoculars! Rising in the eastern sky, Regulus, heart of Leo, is at opposition to the sun on Feb. 18, and chases the Winter Hexagon across the sky.

February 2014 at dawn: This month, Venus attains the peak brilliance of its current morning apparition, which began in mid-January and continues until September. Telescopes and even binoculars reveal Venus now as a crescent, back-lit by the sun. Find Venus before sunrise, and keep track of it—and you can have a daytime sighting! It’ll be especially easy on Feb. 25 and 26, when the crescent moon appears nearby.

For most of February, in morning twilight, you can observe three planets: Venus in the southeast; Saturn in the south; and Mars in the southwest. In the last days of February, a fourth planet appears, once Mercury emerges from its Feb. 15 solar conjunction on near side of sun into the east-southeast twilight glow. Back-lit Mercury is faint at first, but continues to brighten.

Look for these stars within the zodiacal belt: Antares, heart of Scorpius, to the upper right of Venus and lower left of Saturn; Spica near Mars; and Regulus, heart of Leo, in the west far to lower right of Mars and Spica.

In the latter half of February, the waning moon in the morning sky will pass all of these, in west-to-east order: Regulus, Spica, Mars, Saturn, Antares, Venus and Mercury.

Other bright stars at dawn are Arcturus, high above Mars; Spica, in the southwest sky; and the Summer Triangle of Vega-Altair-Deneb, climbing in the eastern sky. The brightest objects visible at morning mid-twilight at start of the month, in order of brilliance, are Venus, Arcturus, Vega and Mars. The red planet nearly doubles in brightness and clearly outshines stars Arcturus and Vega after mid-February.

On Feb. 11, the revolution of spaceship Earth around the sun will be carrying us toward Saturn. A week later, on Feb. 18, Earth passes between the sun and Regulus, and that star appears at opposition—180 degrees from the sun. On Feb. 28, Earth is heading toward a point less than 5 degrees above Antares.

Looking ahead, on April 8, Mars takes its turn at opposition as our planet passes between that planet and the sun. On May 30-31, three weeks after Saturn appears at opposition, Antares will appear at opposition and be above the horizon nearly all night.


A Note on the Sighting of Opposing Crescent Moons, Dec. 31, 2013 and Jan. 1, 2014: A New Record?

On the very clear morning of Tuesday, Dec. 31, Alexander Seidler and I drove to a high spot in a residential area in the northwest corner of Palm Springs. From that site, we had an excellent view of the Coachella Valley below—and spotted the old crescent moon soon after its rising in the east-southeast shortly before 6 a.m. Pacific Standard Time.

We saw it first with 8x42 binoculars, then immediately with unaided eye; we then enjoyed the view through an Orion SkyQuest XT4.5 Dobsonian Reflector at 45x. Alex was able to hold the moon in view with unaided eye until 6:34 a.m., when it was 20 hours and 40 minutes before new. We remained at the site until sunrise and observed a spectacular green flash.

That day, I examined some topographical maps to help me select a different site to provide us with an unobstructed view of the young moon on the evening of Jan. 1. I picked a site in a residential area on the upper-northern part of Desert Hot Springs with a clear view toward Banning Pass in the west-southwest. I visited the site on the evening of Dec. 31 to make timed observations of Venus. Doing so helped me predict, within narrow limits, where the very thin young moon would appear at earlier stages of twilight on Jan. 1.

We returned to the Desert Hot Springs site with two others on Jan. 1, equipped with two pairs of 8x42 binoculars, a pair of 15x70’s, and two Orion SkyQuest 4.5-inch Dobsonian reflectors: one at 36x and the other at 45x. As we looked through some thin streaks of cirrus cloud, Alex was the first to spot the extremely thin crescent, through the 4.5-inch at 36x, at 5:11 p.m. PST, when its age was 13 hours, 57 minutes.

Another observer in our party of four, Andrew Smith, spotted it through the same scope within a few minutes, and I finally caught a brief glimpse using the other telescope at 45x.

A fourth member of our evening party, Misti Rausch, never did see the moon that evening. It may have been because she lost her eyeglasses and had difficulty adjusting the telescope to the appropriate focus. When I tried to refocus my telescope with my eyeglasses on immediately after I saw the crescent to enable others to have a look, I was unable to see the moon and never did recover it. None of us observed the moon with the binoculars or with unaided eye that evening.

The time interval between Alex's last observation of the waning moon on Dec. 31 and his first observation of the waxing moon on Jan. 1 was 34 hours and 37 minutes. As far as I know, this may be a new record for the shortest time interval between sightings of opposing crescents. Stephen J. O’Meara spotted opposing crescents 35.7 hours apart exactly 19 years earlier, on Dec. 31 and Jan. 1, 1994-1995 (see his account in the May 1995 issue of Sky and Telescope, Page 105), but he was observing from the big island of Hawaii, where winter days are longer than in Southern California—so it would not have been possible for him to see the opposing Moons as close together in time as we did.

We are eagerly awaiting our next opportunity to see opposing moons on consecutive days, on Feb. 28 and March 1. At civil twilight here in the Coachella Valley, the crescent at dawn on Feb. 28 and at dusk on March 1 will both be just over 18 hours from the new moon, which happens to occur at 12 a.m. on March 1.

Robert C. Victor was a staff astronomer at the Abrams Planetarium at Michigan State University. He is now retired and enjoys providing skywatching opportunities for school children in and around Palm Springs. Robert D. Miller, who provided the twilight charts, did graduate work in Planetarium Science and later astronomy and computer science at Michigan State University and remains active in research and public outreach in astronomy.

Published in Astronomy