The Young Moon with Binoculars or Telescope
Posted 20 May 2004 - 10:11 AM
As a general rule of thumb, the Sun - Moon elongation has to be at least 7 degrees for some portion of the lunar limb to have some sunlight cast on it viewable from our perspective. It also helps when the Moon is directly above or close to directly above the Sun at either sunset or sunrise (little or no azimuth off-set). The elongation can be sufficient but if the off-set is more azimuth than altitude, that minimizes the chances of finding the Moon. As it is, I have found that attempts at finding the Moon are virtually impossible until at least 15 to 20 minutes after sunset or within 15 to 20 minutes of sunrise.
Attempts for young or old crescents within 20 hours of new moon will often have the Moon within 2 to 3 degrees of the horizon when favorable search times begin so you also need extremely clear, haze free skies and an unobstructed horizon.
Young moon searches are probably more difficult because if your search apparatus is portable, you really cannot polar align to aid your search and unless you prefocus your telescope or binocular on infinity the evening before, you may be missing an otherwise viewable crescent because of focus. Even if focused on infinity, your eyes have little to focus on looking thru the equipment so they are searching for focus much like an autofocus camera does when you point it at the sky without an obvious target. Still and all, young Moon searches are more popular than old Moon searches because they happen at a more convenient time.
An old Moon search can be aided by polar alignment, allowing one to intercept the Moon using setting circles, and as you can begin your search when the stars are still visible, focus is not as much of an issue. Once the Moon is found, as long as you can continue to see it, your time will get closer and closer to new, unlike a young Moon search when your best time is the first instant it is found. For either search you need a horizon unobstructed down to the true horizon. Additionally a landmark can help. By noting the position of the Sun at sunset a few days before a young Moon attempt you can adjust your position to put a distant landmark near your search area to aid the hunt.
While hunts with binoculars will typically take away the advantage of a driven mount and possibly exact positioning via digital or analog setting circles; they do bring to the table the advantages of two eyed viewing and correctly oriented images.
This year we have several good opportunities for hunting down young and old crescent Moons. Note that all ages are based upon discovery at exactly 20 minutes after sunset or 20 minutes before sunrise. I used the Observer's Handbook 2004 to gather times of new Moon and I used Sky Map Pro for the rest of the calculation (set for my location in New Orleans). They include:
Wednesday, 5/19 - Young Moon (20 hours, 17 minutes) at 8 09 21 PM CDT with the altitude being 4 degrees, 8 minutes and the elongation 9.5 degrees (New Moon is at 11:52 PM CDT on 5/18)
Saturday, 7/17 - Young Moon (13 hours, 58 minutes) at 8 22 22 PM CDT with the altitude being 2 degrees, 43 minutes and the elongation 8.2 degrees (New Moon is at 6:24 AM CDT on 7/17)
Sunday, 8/15 - Old Moon (14 hours, 16 minutes) at 6 08 AM CDT with the altitude being 2 degrees, 6 minutes and the elongation 8.4 degrees (New Moon is at 8:24 PM CDT on 8/15)
Wednesday, 10/13 - Old Moon (15 hours, 6 minutes) at 6 41 36 AM CDT with the altitude being 2 degrees, 21 minutes and the elongation 8.2 degrees (New Moon is at 9:48 PM CDT on 10/13)
Note too that the 10/13 Old Moon is the first day of the DSRSG for this year.
The known record for a young Moon sighting is by Robert C. Victor of Abrahms Planetarium on 5/5/89 with an age of 13 hours, 28 minutes and a Sun - Moon elongation of 8.24 degrees. The best that I have done to date is 19h 15 min, on 11-11-96. The Sun - Moon separation or elongation was 9.91 degrees.
While there are no hard set rules in documenting young or old Moon sightings, it is best to have your equipment mounted so that a sighting can be confirmed by another in your observing group. A running tape recorder is not a bad idea either. This is helpful in pinning down an exact time. A wwv time signal broadcast near the tape recorder is also a good idea. Photographic evidence is also desireable. Handheld binoculars are not recommended as the movement generated will virtually assure that a very faint crescent with a very low contrast gradient will not be seen. If you use binoculars, mount them. This will also allow your observation to be confirmed by someone else.
While none of the 2004 possibilities will beat any national records, several of them will come quite close. A photo of some of the more challenging ones may set a new photographic record on a national level. Such a photo will show an extremely thin and discontinuous arc.
Late breaking news - I was successful in observing the young crescent on 5-19. Clouds to the west had me questioning whether an attempt was worthwhile so I delayed in getting to my observing location. Equipment used was a University Optics 80 mm f/6.25 refractor on a Bogen 3036 tripod with 3063 pan head. I documented my efforts with an Olympus 3000 digital camera. I forgot my dedicated afocal (TV 32 plossl) eyepiece with adapter at home, so I had to hold the camera up to a 25 plossl eyepiece. This made focus more difficult.
I did however first see the Moon at 8:09 54 CDT for an age of 20 h, 17 m, 54 s, and my first photo, as pictured was at lunar age 20 h, 19 m, 28 s at 8:11 28 CDT. The image is shown as an insert with an additional comparison insert of a 25 h, 56 m crescent from 3-21-04. Also shown is the location of the crescent via a black X, fortunately missing the clouds. Venus is seen to the upper left. The separation of the Sun and Moon at the time of the observation and photograph was just 9.6 degrees, so while the Moon age was about an hour older, technically this one had an arc less illuminated than the one I documented on 11-11-96 as the separation there was 9.91 degrees.
This stuff is a lot of fun!
Posted 20 May 2004 - 10:38 AM
Nice work, Barry! and thanks for sharing the photos. Quite an impressive hunt!
Posted 21 May 2004 - 05:01 AM
last night 5-20 at 5:20 P.M. EDT, the thin cresent made a beautiful picture just below Venus. Any ideas how old that was? I can't find an astronomical source with the exact time of new moon. Closest I could figure is about 23.5 hours old based on local newspaper.
Ahh, I see above Barry's info, which would put me at a day plus 17+ hours. Oh well.
Posted 21 May 2004 - 07:07 AM
Posted 21 May 2004 - 08:13 AM
I think you already figured it out but the 5-20-04 crescent Moon from your New England location was approximately 43 hours old. Most of the really young ones under about 21 hours are virtually impossible to see naked eye and difficult with optical aid. Between about 21 and 24 hours and perfect conditions may permit naked eye viewing if you know just where to look. As I mentioned in my previous post and as we know from faint star observation, unmounted binoculars put the faintest objects out of our reach so I doubt that the thinnest crescent moons can be seen thru binoculars unless mounted. From my own experience, only when the age gets up near about 30 hours will a crescent Moon become obvious naked eye.
Probably the best source for data in the form of an "old fashioned" book would be the data published yearly in the "Observer's Handbook". This 300 page or so publication virtually has it all. It is published by the Royal Astronomical Society of Canada. I started getting these when I joined my local astronomy club back in 1979 (Pontchartrain Astronomy Society - New Orleans). I still have every annual edition on my book shelf. I believe you can order a copy and see an overview at: www.store.rasc.ca
Posted 21 May 2004 - 12:17 PM
Moon was new at 05.52 UT on 2004 May 19.
Posted 21 May 2004 - 11:04 PM
"Crescent Moon Visibility and the Islamic Calendar", by the US Naval Observatory:
Oh, here's a story about the recent world's record, and it was reported in Sky & Tel over a year ago (Feb. 2003):
Ed Cannon - Austin, Texas, USA