EXTREME YOUNG CRESCENT MOONS OF 2012A favorite pastime of many sky watchers, including myself, is seeing how soon after new moon you can spot the emerging lunar crescent. These barely visible slivers appear low in the bright western sky just after sunset. Below is one I photographed from the top of South Mountain a mere 23 hours after the moon turned new on February 14, 2010. Under the right circumstances, moons can be detected that are several hours younger than this.
On January 23, 2012, Arizona observers have a chance to see a delicate infant moon about 17.5 hours after new. Then for an even greater challenge, on December 13, a moon that is only 16.2 hours old might hang around long enough to be spotted.
Both of these young moons will appear roughly in the same part of the skyjust a little above the horizon to the WSW. It is imperative to have a clear view of a low horizon in that direction. A good time to start the search is about 20-30 minutes after sunset.
Binoculars can help you spot these diminutive moons. Their light gathering power and slightly magnified view allows you to see interesting detail. The most fascinating to me is the broken nature of the crescent. This is from mountains and high crater walls on the lunar surface that cast shadows and block small areas of sunlight from fully forming the crescent.
Each year I work out the details of upcoming young moon apparitions for my own location in Phoenix. I include it below for those sky watchers who want to delve a little deeper into this subject and get a more comprehensive picture about the situation. The first two columns show the date and time of all new moons for 2012. The remaining columns give information about when and where that month's moon could/should be first sighted in the Phoenix area. Highlighted rows show months when the first sighting should be less than a day after new moon. All times are MST. For other locations, follow directions given below in the notes for twilight and age.
twilight: refers to the end of "civil twilight" when the sun is exactly 6° below the horizon. The sky is still relatively bright at this time, but it signals a period when you can start looking for brighter objects like the moon and planets. It varies due to time of year and observer latitude, but for Phoenix it is usually about 24-27 minutes after sunset.
These times are for Phoenix. You can find the time of civil twilight for your own location by going to the U.S. Naval Observatory Rise/Set calculation web page. A pull-down box labeled "Type of Table" allows you to choose rise/set information on the sun or moon, or times of the three different types of twilight. At times that site can be painfully slow. If so, try Heavens Above. You will find a wealth of astronomical data there, one being rise/set and twilight information on the sun for any given day. You will need to set your location when you first use the site, but then bookmark the page and your location info will be saved in the bookmark.
age: the age of the young moon at the time of observation in the form hh:mm. In this table it is correct for the end of civil twilight in Phoenix. If you spot the moon at a different time, you can figure the age by determining how much time has passed between new moon and when you first saw it. It should be noted however that many people just use whole hours especially for ages over 24 hours. If you are trying to best a personal record however, minutes do matter.
alt: the altitude in degrees (°) above a perfectly flat horizon. Most typical horizons are actually a degree or two higher than the mathematically calculated flat horizon.
azm: gives the azimuth in degrees (°). This is basically a compass heading with north at 0°, east at 90°, south at 180° and west at 270°. Some people like using this more-precise directional information to narrow the search area when looking for hard to find sky objects.
dir: this is a standard direction translated from the azimuths in the previous column. Much of the time this is all you need when searching for brighter objects.
See Navigating The Sky for more information about measuring degrees of arc, altitudes and azimuths.
All images are copyrighted by Frank Zullo. Please do not use without written permission.