HANK YOU, THANKSGIVING --------------------- John Pazmino NYSkies Astronomy Inc wwww.nyskies.org email@example.com 2015 November 26 Introduction ---------- New York in 2015 entered a new season of lunar occultations of Aldebaran. As the Moon sweeps thru the zodiac, she passes over or miss stars according as the lunar ecliptic latitude and the observer's location on Earth. For many years the Moon missed Aldebaran. Now she is in a run of almost monthly hits, altho some ae not seen from the City by timezone or geographic latitude. The occultation on Thanksgiving morning, 26 November 2015, occurred in clear chilly air. The Moon was almost full and was low in the west at the start of dawn. Preparation --------- For this event I needed a a window facing west with no obstructions like trees or roofs. Of a couple choices, one window was perfect with the Moon in open sky over low skyline. I observed from indoors, to avoid the hassles of setting up outside so early in the day. My plan was to watch the occultation, then turn back to bed for a few more hours of sleep. At the window on the preceding evening of the 25th I moved an end table under the sill to support a table-top telescope. I set the scope case next to the table, ready to unpack it quietly and quickly in the dawn hours. Because my cats roam around at night I dared not try to view thru a completely open window. The pets jump to the sill and could easily slide off with no positive barrier to contain them. In the stead, I then washed the inner glass pane and then latched open the screen and outer glass panes. I finally closed the inner pane, protecting the cars and giving me, hopefully, a clean view thru it of the occultation.. I placed a small folding chair next to the end table. My observing station was now ready to rumble. Eons ago I learned that observing must be done, in so far as practical, under comfort. On the whole, being seated at the telescope is a huge step toward that comfort. At my station ----------- I got up from sleep at 5 AM and dressed in running slacks and sweater. The air was thoroly chilly but probably not freezing. I threw over me a heavy wool bathrobe. I went to the window in dark to keep my night vision. The sky was clear. I didn't purposely hunt for stars. I did notice the Pleiades to the right of the Moon. The Moon, being shortly after full phase, was dazzling. I could not see Aldebaran at all by eye. I unpacked the scope and set it on its drum base onto the end table. I never thought of attaching its equatorial stand because I can follow the Moon by the axis control knobs. I rotated the eyepiece to face my chair and sat down. I got the Moon in the eyepiece right away. She was almost blinding! I scanned the disc for any limb shadow, didn't see any, and browsed around at the rays and spots here and there. The occultation ------------- here was Aldebaran a good way left of the Moon. It was a lucid twinkling point. No other Hyades stars were noticed. I was looking thru a single sheet of window glass that made some distortion in the image. I found that the most pleasing view was with low power, covering the whole lunar disc. Higher power merely showed more window distortion. On & off for the next half hour I checked on Aldebaran. The axis knobs helped me to chase the Moon as she drifted out of the field. Aldebaran creeped closer and closer to the Moon's eastern edge. I mean astronomical east, the leading, edge The sky was starting to brighten with dawn. At 5:46 AM EST, by a wall clock, Aldebaran snapped out of sight behind the Moon. I think it was gone a second earlier as twinkling sometimes blanked it out momentarily. After a few more seconds of inspecting the lunar edge, I knew the star was in fact behind the Moon. I didn't try for a proper timing of the ingress, preferring to enjoy the view at leisure. The wait ----- Aldebaran would return to clear sky in about 45 minutes. As I laid down to rest in bed, the sky continued to brighten. By a quarter after six, again by the wall clock, it was obvious that the sky was already too bright to see any stars. The Moon was still in open sky over roofs, a lot easier to examine with a bright sky around her. The surface markings were far easier to study with the lunar glare abated by dawn.As a matter of technique, many astronomers observe the Moon in twilight to suppress the dazzling of full night. I called it quits since thee was for me no hope of spotting Aldebaran at the egress. Closing the station ----------------- I made sure my cats were no where near me and quickly opened the inner pane, pulled down the screen and outer panes. Then I closed the inner pane. I packed the scope, whose case was near the radiator. Heat for the house wa starting to come up. I left the packed scope by the end table and went back to sleep. A couple hours later, in bright morning daylight, I woke up for the day. put away the scope case and straightened the table, removed the chair. The cats were already scampering around for breakfast. Selenehelion? ----------- The almost Full Moon for this occultation set shortly after sunrise. Was this a selenehelion? Stricta mente it wasn't because a classical selenehelion requires that the Moon be in eclipse when seen together with the Sun at sunrise or sunset. We had a true selenehelion in New York during the 8 October 2014 lunar eclipse at sunrise. The sky near the Moon was mostly cloudy, spoiling the view for most observers in the City. By a relaxed definition the Moon seen with the Sun at sunrise or sunset may be within a stated tolerance of the exact Full Moon. Under this definition we can have several selenehelia each year. I mysyself allow +/-6 hours centered on the Full Moon hour. The tolerance for relaxed selenehelia is a personal choice but it can not excede /-12 hours, else the Moon is really too far from Full phase. For the Aldebaran occultation the Full Moon occurred on 2015 November 25 17:45 EST.. Even adding the maximum reasonable leeway, +12 hours, this gives the latest hour for a possible selenehelion of 05:45 on the 26th. This happened to be, wholly by coincidence, when Aldebaran entered the occultation. By sunrise, 06:54, the window for selenehelion was closed and the Moon herself set at 07:20. We did not have a selenehelion for the Aldebaran occultation. We did enjoy a very large Moon setting some 35 minutes after sunrise. Aldebaran occultations --------------------- I noted that we are in a new season for occultations of Aldebaran. Stars along the zodiac are occulted only if the Moon's orbit swings her over the star as seen from Earth. The lunar orbit is inclined about 5-1/2 degree from the ecliptic, with the Moon completing a circuit of latitude +/-5-1/2 degree per month. The 'month' is NOT the sidereal or synodic month. It is the draconic month, the period between successive crossings of zero degree latitude, either on the northward leg of the orbit or the southward. These zero points, the nodes of the orbit, migrate westward thru the zodiac, against the order of the signs. The Moon crosses a node a little early relative to the sidereal month. A full migration of the nodes , a sliding of the whole orbit, takes about 18 years. The effect is that a star in the zodiac within the latitude corridor of the Moon is occulted in certain years and is missed in others. The interval between occultation seasons is about 18 years. The season lasts from only a couple years for stars far from the ecliptic, near the limit of excursion of the Moon,like for Aldebaran. The current season of Aldebaran occultations began with the event of 2015 January 29 and ends with that of 2018 September 3. This span covers all occultations over the whole Earth, not just for New York. New York misses most events for latitude and timezone displacement. Those geometricly visible from the City are listed here: ----------------------------------------------------- ALDEBARAN OCCULTATIONS FOR NEW YORK IN CURRENT SEASON ----------------------------------------------------- T date and hour | %SL | EST | Sun | star | Sep' -----------------+------+------+-----+------+----- 05 Sep 2015 05:22 | 52- | 23:19 | -42 | 7 | 9 low alt 02 Oct 2015 13:03 | 74- | 09:30 | +36 | 14 | 1 daytime 26 Nov 2015 09:42 | 99- | 06:10 | -+8 | 11 | 9 large Moon 20 Jan 2016 02:29 | 83+ | 22:06 | -57 | 59 | 8 10 Apr 2016 22:19 | 17+ | 18:22 | 0 | 43 | 3 twilight 04 Jun 2016 19:05 | 0- | 15:12 | +45 | 38 | 5 daytime 29 Jul 2016 11:09 | 23- | 05:37 | +7 | 50 | 13 daytime 19 Oct 2016 06:33 | 86- | 01:15 | -53 | 60 | 8 13 Dec 2016 04:27 | 99+ | 23:50 | -73 | 64 | 4 large Moon 05 Mar 2017 02:57 | 47+ | 23:22 | -54 | 14 | 15 brief event 28 Apr 2017 17:33 | 7+ | 12:05 | +64 | 55 | 1 daytime 22 Jun 2017 14:36 | 4- | 09:23 | +53 | 62 | 5 daytime 12 Sep 2017 12:25 | 58- | 08:32 |++32 | 40 | 4 daytime 15 Oct 2017 11:24 | 20- | 05:14 | -11 | 39 | 9 06 Nov 2017 02:29 | 95- | 20:27 | -42 | 21 | 4 large Moon 31 Dec 2017 00:28 | 93+ | 18:48 | +24 | 43 | 11 large Moon 23 Feb 2018 17:12 | 54+ | 11:20 | +38 | 0 | 5 low alt ------------------------------------------ The columns are: UT date and hour - The time when the occultation is greatest any where on Earth, which for sure is not in New York %SL - sunligghted fraction of lunar disc. + for waxing; -, waning EST - EST of mid event in New York City. Ignores EDST. Watch for an intervening midnight crossing between UT and EST. Sun - altitude of Sun at mid event. + for Sun above horizon in daylight; -, under horizon in twilight or nighttime star - altitude of Aldebaran at mid event, always above horizon Sep' - separation in arcmin of Moon and Aldebaran at mid event ----------------------------------------------------------- Altho we are favored with many Aldebaran occultations in this current series, some are challenged by impediments. These are noted after the Sep' column. A few occultations have multiple impediments but only one of them is noted. Which of these events you may observe depends on your observing skills and tools and the instant sky conditions. Rule-of-19 -------- This occultation obeys the Rule-of-19. Given the date of any one instance, others occur at 19-year intervals on the same date. The series continues for several rounds before, like just about all other 'cycles' in lunar motions, falls apart. The expired series is replaced by a new one. The previous Rule-of-19 Aldebaran occultation took place on 25 November 1996. The one day discrepancy is a calendar jiggle. New York missed it for happening after moonset. The Moon was full, 100% lighted. The next Rule-of-19 event is on 2034 November 26 at 05:03, for mid event. We see this one almost a duplicate of the 2015 show with the 99% lighted Moon low in west. Mind well that the rule, like the similar Saros cycle, does not give the date of the very next or previous event! Between the three Aldebaran occultations of 1996, 2015, 2034 there are many others. Each follows its own Rule-of-19 cycle. Conclusion -------- I missed the September 2015 event for low altitude. The Moon was behind skyline and trees. I lost the daytime occultation in October 2015. I just could not ever catch sight of Aldebaran in daylight against the Moon. The sky was too hazy. Now om Thanksgiving Day of 2015 I saw half of this occultation. I missed the reappearance of the star due to overly bright sky. In spite of these duds, I'll be watching for the future occultations. Aldebaran occultations are of special meaning for me because the very first occultation I watched was of Aldebaran on July 19th, 1960 in predawn hours. The Moon ws a waning crescent with Aldebaran ingress at the bright limb.. Yes, thank you, Thanksgiving!