lew@ihuxr.UUCP (Lew Mammel, Jr.) (09/26/84)
The Stardate posting of Sept. 10 on "The Harvest Moon" contained this statement: ... this full moon rises on a path that makes a very narrow angle with the horizon -- so the Harvest Moon stays near the horizon longer than most full moons. This is incorrect. The moon rises by its diurnal motion, not its orbital motion. The referred to narrow angle makes the harvest moon rise at nearly the same time for several nights in a row. The midsummer full moon will skim the horizon as suggested since its diurnal path makes the narrowest angle with the horizon. Lew Mammel, Jr. ihnp4!ihuxr!lew
ken@ihuxq.UUCP (ken perlow) (09/28/84)
-- >> The Stardate posting of Sept. 10 on "The Harvest Moon" contained this >> statement: >> ... this full moon rises on a path that makes a very narrow >> angle with the horizon -- so the Harvest Moon stays near the >> horizon longer than most full moons. >> This is incorrect. The moon rises by its diurnal motion, not its orbital >> motion. The referred to narrow angle makes the harvest moon rise at >> nearly the same time for several nights in a row. >> The midsummer full moon will skim the horizon as suggested since its >> diurnal path makes the narrowest angle with the horizon. >> Lew Mammel, Jr. ihnp4!ihuxr!lew Stop, you're both right! The harvest moon phenomenon is the rising of the full moon at approximately the same time on successive nights instead of the about average 50 min. per day lag. The moon's azimuth at harvest moonrise changes quite dramatically, however--noticeably northward each night. This phenomenon is repeated, much less dramatically, a month later with the so-called "hunter's moon". The moon's orbital motion is very close to the plane of the ecliptic (that's the plane of the solar system that contains the constellations of the Zodiac). The angle of the ecliptic with the eastern horizon is about as narrow as it gets at about sunset on the first few days of fall. The ecliptic traces out a precessing path in the sky once per siderial day (that's any particular star-rise to next star-rise, which is a little less than a solar day--sunrise to sunrise--because of the extra rotation needed to compensate for a day's worth of revolution about the sun). So, the maximum and minimum ecliptic-to-horizon angles occur once each day, about 4 minutes earlier every day. Thus, the "skimming" phenomenon is due to the once-per-year coincidence (or close to it) of the minimum angle with a full moonrise. The phenomenon is obviously generalizable to any object in the Zodiac at the First Point of Aries, for instance, sunrises on the first days of spring. (Astronomers really use that term "First Point of Aries", a paean to the astrological history they try so hard to disassociate themselves from). -- *** *** JE MAINTIENDRAI ***** ***** ****** ****** 27 Sep 84 [6 Vendemiaire An CXCIII] ken perlow ***** ***** (312)979-7188 ** ** ** ** ..ihnp4!ihuxq!ken *** ***
kaufman@uiucdcs.UUCP (10/01/84)
/* Written 12:41 am Sep 28, 1984 by ken@ihuxq in uiucdcs:net.astro */ -- >> The Stardate posting of Sept. 10 on "The Harvest Moon" contained this >> statement: >> ... this full moon rises on a path that makes a very narrow >> angle with the horizon -- so the Harvest Moon stays near the >> horizon longer than most full moons. >> This is incorrect. The moon rises by its diurnal motion, not its orbital >> motion. The referred to narrow angle makes the harvest moon rise at >> nearly the same time for several nights in a row. >> The midsummer full moon will skim the horizon as suggested since its >> diurnal path makes the narrowest angle with the horizon. >> Lew Mammel, Jr. ihnp4!ihuxr!lew Stop, you're both right! The harvest moon phenomenon is the rising of the full moon at approximately the same time on successive nights instead of the about average 50 min. per day lag. The moon's azimuth at harvest moonrise changes quite dramatically, however--noticeably northward each night. This phenomenon is repeated, much less dramatically, a month later with the so-called "hunter's moon". The moon's orbital motion is very close to the plane of the ecliptic (that's the plane of the solar system that contains the constellations of the Zodiac). The angle of the ecliptic with the eastern horizon is about as narrow as it gets at about sunset on the first few days of fall. The ecliptic traces out a precessing path in the sky once per siderial day (that's any particular star-rise to next star-rise, which is a little less than a solar day--sunrise to sunrise--because of the extra rotation needed to compensate for a day's worth of revolution about the sun). So, the maximum and minimum ecliptic-to-horizon angles occur once each day, about 4 minutes earlier every day. Thus, the "skimming" phenomenon is due to the once-per-year coincidence (or close to it) of the minimum angle with a full moonrise. The phenomenon is obviously generalizable to any object in the Zodiac at the First Point of Aries, for instance, sunrises on the first days of spring. (Astronomers really use that term "First Point of Aries", a paean to the astrological history they try so hard to disassociate themselves from). -- *** *** JE MAINTIENDRAI ***** ***** ****** ****** 27 Sep 84 [6 Vendemiaire An CXCIII] ken perlow ***** ***** (312)979-7188 ** ** ** ** ..ihnp4!ihuxq!ken *** *** /* End of text from uiucdcs:net.astro */