SKY REPORTER: Shine on Harvest Moon

A lunar eclipse from September 11, 2003.

Focus of this month’s Sky Reporter shifts from Perseid meteors to meteorological prospects for Sunday evening, September 27, when, weather permitting, we anticipate a wonderful evening of Moon watching. That night we’re due for a triple header—the Harvest Moon will also be a “Super Moon,” about as big as any Full Moon can ever appear. And, the super-sized lunar disk will be totally eclipsed during convenient evening hours for viewers in eastern states and Canada, and at times during the night across the Americas, Europe, Africa, and western Asia.  

 The partial umbral phase, when we clearly see a “bite” gradually disappearing from the lunar disk, begins at 9:07 p.m. Eastern Time. Then the Moon will be a comfortable 26 degrees above our east-southeast horizon in New York City—that’s an altitude equal to about two and a half fist lengths seen at arm’s length. Totality starts at 10:11 p.m., mid eclipse is at 10:48, totality ends at 11:23, and the partial umbral phase concludes soon after midnight at 12:27 a.m. ET. 

 Only once did I experience a total lunar eclipse that was REALLY total—the lunar disk was invisible at mid-eclipse December 9, 1992, when air high above much of the planet was laden with volcanic dust blasted from Mt. Pinatubo in the Philippines during devastating eruptions the previous year. Dust that night completely masked the usual ruddy hues of a lunar eclipse. Generally we see degrees of orange-red shading on the Moon’s disk caused by sunlight refracted into Earth’s shadow after passing through the ring of sunrises and sunsets that perpetually encircles our planet. During these atmospheric transits shorter wavelengths of violet, blue, and green are scattered around the sky and left behind, while longer wavelengths of orange and red color travel to the Moon, then reflect back to eclipse viewers across half our planet. 

 Three circumstances will make this month’s eclipse special (if we luck out with weather). It’s the night of the annual Harvest Moon, an occasion steeped in traditions heralding the advent of autumn. Due to the rather low angle of the zodiac relative to the eastern horizon at this time of the year we have relatively short periods of fading twilight before brilliant gibbous moons rise on several successive evenings just after the night of the Harvest Moon. Brief periods of twilight, before moonrise illuminated fields, provided extra time for agricultural workers to hastily bring in harvests before unavoidable turns of nature might have compromised crops.  

 This year’s Harvest Moon reaches maximum “fullness” at 10:52 p.m. Sunday evening, September 27, when Moon and Sun are on diametrically opposite sides of Earth. That’s only four minutes after midpoint of the night’s total eclipse. 

 Next facet of the Harvest Moon extravaganza is the Moon’s apparent size. Every month of every year the Moon’s orbit brings it to an apogee point when it’s furthest from Earth and also to another orbital place called perigee when the Moon is closest to our world. Once every year a full lunar phase occurs near the perigee date and many folks report the Moon’s disk looks somewhat larger than normal. This month Lunar perigee takes place 9:49 p.m. ET, just an hour and three minutes before the moment when the Harvest Moon is technically “Full” and just 59 minutes before mid-point of the lunar eclipse. That’s a very special coincidence. 

 A Super Moon is said to occur when its center to center distance from Earth is less than 224,851 miles. When September’s Harvest Moon reaches perigee on the 27th, its distance from Earth will be just 221,753 miles, so it fits the “super” definition. That evening it will appear 30% larger in area than the Full Moon of March 5, when it was near apogee, 252,516 miles from Earth. 

 This month, evening temperatures should be ideal and, if the weather is clear, the stage is set for eclipse viewing parties to blossom the evening of the 27th. Binoculars and low magnification wide field telescopes are fine accessories for lunar eclipse experiences. It will also be an opportunity to snap some images. Zooming can show more lunar features but will also magnify camera vibrations. A tripod or other mounting rig avoids that issue. Chairs facing southeast, a table decked with refreshments, plus family and friends can also enhance a memorable evening of eclipse savoring. 

The Moon

Planets

Of the planets visible with unaided eyes, only Saturn will be above the horizon during evenings of September.

 Observers in the northeastern US and eastern Canada can enjoy a view of the Moon sliding eastward between us and first magnitude star Aldebaran, brightest in Taurus, shortly around midnight on Friday night September 4/5. Binoculars or a telescope will be needed spot the star just next to the illuminated half of the lunar disk. Aldebaran will abruptly disappear as it is occulted by the Last Quarter Moon (yes it does look like a half moon). When watching from New York City Aldebaran will be winked out by the Moon’s edge adjacent to Mare Imbrium at about 11:55 p.m. Friday night. Aldebaran will suddenly reappear at about 12:40 a.m. adjacent to the lunar limb near Mare Crisium.  For local viewers, the Moon will only be four degrees above the eastern horizon when the occultation event starts, so the sky must be quite clear near the horizon for the observation to be accomplished. For other sites around the northeast, you can visit Lunar Occultations for times specific to other locations.   

 Mercury is at its greatest eastern elongation (angular separation eastward from the Sun) on September 4. However at this time of the year this night elongation of 27 degrees of arc doesn’t help us much for seeing that elusive little world. Elongation is measured along the ecliptic, which at this time of the year makes a low angle with the horizon around sunset. As a result, on September 4 Mercury is a scant three degrees above the horizon at the end of civil twilight. 

 The waning crescent Moon may be seen above the eastern horizon about one-third of the way between Venus and Mars, after 4:30 on the early morning of September 10. 

 The waxing crescent Moon is about three degrees northwest of Saturn during early evening on the 18. 

 Autumn begins in the northern hemisphere 4:21 a.m. Eastern Time on the morning of September 23. The Sun is above a point in the Indian Ocean on the equator at East longitude 52 degrees and 53 minutes. 

 Mars is near Venus and the first magnitude star Regulus, brightest in Leo during the pre-dawn hours of Thursday September 24.

 Sunday evening, September 27, the great 2015 Harvest-Super-Total Eclipse Moon will rise!