Saber's Beads
Contents
Saber's Beads
(unofficial name)
Image by Jerry Lodriguss (contrast enhanced and "Saber's Beads" caption added by Stephen Saber) The original photo was taken from Batsto, NJ at 00:03 UT on April 10, 2005. It shows the Moon with 1.39% illumination, that is, at an elongation of 13.5° from the Sun.
Description
Lunar phase phenomenon seen on extremely young and old crescents. This necklace of staggered brightness peaks along very thin crescents is reminiscent of the beautiful 'string-of-pearls' effect seen near 2nd and 3rd contacts during a total solar eclipse. - saberscorpx
Additional Information
- While spotting stray beads at the tips of older waxing and waning crescents is quite common, the entire limb segmentation reveals itself much closer to New Moon. As the eclipse counterpart is initiated by direct sunlight seen through our moon's valleys, Saber's Beads are detected by the early and last angular illumination of the mountainous regions. Luna's rugged topography, distance, and constant libration will also vary the Beads' appearance, which is often enhanced by associated low-altitude scintillation. - saberscorpx
- Depending on how they are defined, there seems to be some question regarding the attribution of Saber's Beads to mountainous regions at the Moon's limb. As demonstrated in the When Maria are Bright LPOD, the mountainous regions seem more to cause dark breaks in the central parts of the typically observed thin crescents. There is also some question as to whether the "entire limb segmentation" predicted at the last moments of illumination prior to New Moon has actually ever been observed, how "segmentation" is defined, the elongation at which it is said to occur, and (if observed) whether it is intrinsic to the Moon or an artifact of imperfect visibility. - JimMosher
- Very thin lunar crescents are difficult to see because they have to be observed close to the Sun, and their brightness is only marginally greater than the sky background. To place the Sun out of view, they are also typically observed through the imperfect "seeing" close to the horizon. As a result of both of these factors, the observer's impression of such fundamental things as the length and continuity of the crescent is generally uncertain and can change drastically depending on the sky conditions. Links to web pages with additional examples illustrating the photographic appearance of thin crescents at a variety of elongation angles can be found on the Danjon Limit page. Images of the thinnest crescents usually have to be enhanced to bring out detail. This can (as in the above photo) introduce a graininess which may or may not be intrinsic to the Moon. The Extreme Crescents LPOD shows what are probably the thinnest crescents photographed by amateurs (at an elongation from the Sun of about 5°). These are well beyond the limit of what can be seen visually, and very heavy processing was required to make the crescent visible at all. As a result, it is difficult to be sure how much of what they show is real and how much an artifact of the processing. Nonetheless, they appear to show a faint continuous crescent punctuated by bright patches whose locations are generally, but not completely, consistent from photo to photo. Unfortunately the orientation of the camera was not documented accurately enough to correlate the bright patches with specific surface features at the Moon's limb. How still thinner crescents look appears to be unknown. - JimMosher
Nomenclature
- Named for Stephen Saber, American musician and astronomer (1972- present). - saberscorpx
- This informal name was coined on May 28, 2006 in the "New Moon Spotting Contest" on the Cloudy Nights Lunar Observing forum. In response to amateur astronomer Stephen Saber's posting "Slivers this size show staggered brightness peaks along the crescent, reminiscent of mini-Bailey's beads. We need a name for these... ", contest host (and fellow amateur) Curt Renz commented "Thanks for your fine reports, including your description of "Saber's" beads"; and Carol Lakomiak independently added "sprinkles moondust and waves magic wand… I hereby christen them Saber's beads!". The crescent with staggered peaks that Stephen was describing was observed from Rock Island, IL at 01:36 UT (with 15x63 binoculars) and at 01:51 UT (by naked eye). The illumination would have been 0.89%, and the elongation of 10.8°. Neither Curt nor Carol observed the crescent, so the name was proposed based solely on Stephen’s description of it. The aptness of the name was subsequently confirmed by fellow amateur "Tommy", who stated that as viewed through 10x50 binoculars from southside Chicago at 01:42 UT, " the moon's shimmering paper cresent [impossible to see with the naked eye] did sparkle like the photos of a solar ecilpse, a beautiful sight". Although not mentioned in the original postings, Saber's observation of the maximum similarity of the crescent to solar eclipse contacts was observed, with nautical twilight approaching, using a 90 mm (aperture) Maksutov telescope in addition to the 15x63s binoculars, at 02:10 UT, when the Moon was 2° above the horizon (elongation 11.1°; 0.93% illuminated) (Saber, private communication, 2008). Photos of this particular crescent were subsequently posted in a different thread on the Cloudy Nights forum. One photo, obtained by amateur Tony Cook in Leeds, England, shows the slender crescent Moon at 20:59 UT (elongation 8.8°) extracted from photographic noise. The other, obtained by Andrew Cooper in SE New Mexico, appears to have been taken at around 2:30 UT (the exact time was not given), at an elongation ~11.2°, very similar to the width of the crescent that reportedly exhibited Stephen's eclipse-like mini-beads. - JimMosher
- The term first appeared in print in a Letter from Richard Cone, of British Columbia, on p. 14 of the September, 2006 issue of Astronomy magazine. In his letter, Cone noted that "within 24 hours of New Moon, staggered brightness peaks along the limb exhibit the lunar phenomena known as Saber's Beads." He does not say if he had personally observed the phenomenon.- JimMosher
- Like most informal names, the term Saber's Beads appears to have been used in a variety of ways, and to describe a variety of phenomena. For example, taking its cue from the Cloudy Nights discussion, but using the term in a different way, the January 23, 2007 Yesterday's News LPOD used it to refer to a string of detached bright points seen beyond the southern cusp of a rather thick crescent Moon. Although correctly described as an edge-on view of the detached sunlit peaks often seen in advance of the terminator, these particular "beads" were said to be an "unusual phenomenon". As noted in the comments to that LPOD, and Saber's comments under Additional Information (above), such points of light are actually very commonly observed and had, in fact, been described by Galileo Galilei in his first telescopic observations of the Moon. They have undoubtedly been described many times since. - JimMosher
- The increasing use of the term Saber's beads in the amateur community to describe detached points of light in the crescent's cusps (including in the LPOD) was also noted in Peter Grego's lead article in the March 2007 issue of his BAA Lunar Section Circular, although it was again remarked that that particular phenomenon had been frequently observed in the past. The idea that the slender crescent of the 1 day old Moon would also break into "beads" was regarded as something new, requiring further observation. - JimMosher
- The segmented, but not necessarily "bead"-like, appearance of very slender crescent Moons has been frequently commented upon; although some very thin crescents have appeared unbroken to some observers. Whether a similarity to the Baily's Beads seen in solar eclipses had ever been noted before, and whether a comparable bead-like stage in lunar crescents even exists, is more difficult to establish. It is also unclear from the name's history if Saber's beads was originally meant to imply that a 0.9% illuminated crescent is intrinsically bead-like, or if the name was only meant to imply that something "resembling mini-Baily's beads" can appear when a slender crescent is seen under imperfect viewing conditions (i.e., when it is broken by bad seeing). See More Beads and Slivers for additional discussion of Saber's beads on the Cloudy Nights Lunar Observing forum. - JimMosher
- According to Stephen Saber, the term Saber's Beads can be correctly applied to "the culminating necklace of … any illumination which visually imitates the moments before or after a solar eclipse" (Saber, private communication, 2008). - JimMosher
LPOD Articles
Yesterdays News When Maria are Bright Extreme Crescents
