Many lunar observers are thorough to the point of obsession, and include on their observational reports a "lunation number" along with numerous other calculations for solar colongitude, colatitude and assorted data. The numbering of the Moon's cycle of phases, known as lunations, officially began on 16 January 1923 at the instigation of Ernest Brown (1866-1938), a mathematician/astronomer born in Hull who emigrated to America as a young man. His work greatly improved upon lunar motion theory. In 1896 Brown wrote his "Introductory Treatise on the Lunar Theory". Recently reprinted, I have been reliably informed the book is a delight for the astro-mathematically-minded. Brown's life work led to the publication in 1919 of precise mathematical tables of the Moon's motions which took into account of all known variables in the Moon's path through space. This work firmly re-established our satellite in its ancient role as humanity's chief marker of time. Although crystal and molecular clocks in the laboratory are the best way of measuring very short time intervals, the Moon may still be regarded as an extremely accurate long-term cosmic clock.
Brown has been honoured with a crater on the Moon - a 34 km impact feature nestling in the lunar southern uplands, some 90 km southwest of the prominent ray crater Tycho and overlain by substantial amounts of light coloured ejecta in Tycho's rays. Remarkably, Brown's crater actually resembles a wristwatch, with its southeastern wall intruded upon by Brown E - complete with an irregularity on its rim that looks like a winding knob! There is even some detail on the floor of Brown E that looks like hands on a watch face - when the feature is viewed with south at the top, the time according to the crater reads a quarter past five! This is a fitting, if entirely unintentional example of lunar simulacra in tribute to a man whose work has helped humanity mark time to an exquisite degree of accuracy - just as the lunar crater Messier, named in honour of the famous 18th century comet discoverer, looks like a cometary nucleus with its tail formed by a narrow ray system.
To view Brown this month observe on the evening of the 9th and a couple of days afterwards when it has emerged from the terminator, or a fortnight later on the morning of the 22nd when it is illuminated a low lunar evening sun. Try spotting detail on the floor of Brown E - to discern the central elevation you will probably need to use a 60 mm refractor at high powers, with finer detail on the western floor visible in a 150 mm reflector. There is some dusky shading on the floor of Brown itself, adjoining the north wall of Brown E. This may be a dark lava flow and is visible when the feature is illuminated by a late morning or early evening lunar Sun.A Very Old, Very Slender MoonAt around 6.50 UT on the morning of 29 November, the Moon will rise above the southeast horizon, an extremely narrow crescent nearing the end of lunation number 926. To see the crescent Moon this morning will require a really good horizon and extremely clear weather conditions in a location far from urban smog and sodium skyglow. At 7.30 the Moon will be just 18.75 hours away from New, with a mere 0.7 percent of its disc illuminated, lying some 5 degrees above the horizon. If you have binoculars, sweep the southeast horizon is a slow and deliberate manner - try to keep your binoculars as steady as possible by using a tripod or by supporting your elbows. There is some opportunity to capture this remarkable sight photographically. If you are fortunate enough to succeed in seeing the Moon you'll notice that its limb will appear only partly illuminated, and not a semicircle. This is because the lunar surface isn't smooth, and on close scrutiny the illuminated fraction of the limb will seem to be irregular and broken into numerous beads of light - the tops of mountains and crater rims interspersed with lunar valleys. After 7.30 the skies will be brightening, with sunrise at around 8.00. If you do manage to spot the Moon at such a narrow phase, do let Astronomy Now hear about your accomplishment and send in any photographs you have taken. Not many amateur astronomers have been privileged to have seen such a sight, and the opportunity does not come around too frequently.
