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Autumnal Equinox 23 September, 2015, 1:22 AM, PDT

September 22, 2015

This year we report on that other large object in the sky, known as the sun.

Our Sun (Alan Friedman ~ 4/22/14, on NASA site)

Not a rotting peach, but our Sun – 860,000 miles in diameter, 8 light-minutes away (Alan Friedman ~ 4/22/14, on NASA site)

The next event is the Autumnal Equinox, scheduled in Los Angeles for September 23, 2015 at 1:22 AM PDT (or 0822 UTC – Universal Time Coordinated, if you prefer).  Sunrise will be at 6:42 AM, daylight will last 12 hours, 6 minutes, 50 seconds (12:06:50); sunset is at 6:49 PM and nighttime is 11 hours, 53 minutes (rounded).  You will note that these periods of day and night are not equal. Day and night will be nearly equal on Sep. 26, with 12:00:32; sunrise is at 6:42 AM, sunset is at 6:42 PM.

Definition of the term 
Autumnal: Of or pertaining to Autumn [Latin autumn(us)]
Equinox: When the sun crosses the plane of the earth’s equator [from Latin aequinoctium, the time of equal days and nights].

Equinoctial daytime exceeds nighttime for two reasons
First: Sunrise occurs when the leading (upper) edge of the rising sun first becomes visible above the horizon.  Sunset is when the trailing (not the lower) edge drops below the horizon.  The width of the sun adds about six minutes of daylight.
Second: Refraction of the sun’s rays by the earth’s atmosphere permits us to see the sun both before it has actually risen and after it has actually set, adding several minutes each to sunrise and sunset.

Seasonal Fluctuation
Because the two equinoxes (vernal and autumnal) mark when the sun crosses the celestial equator (the plane of the earth’s equator projected into space), these are also the only days of the year when the sun rises exactly in the east and sets exactly in the west.  The earth’s axis (and equatorial plane) is tilted 23.4° with respect to the plane of the earth’s orbit around the sun. In the northern summer the earth’s

Northern Summer (famous artist - name withheld by request)

Northern Summer (famous artist – name withheld by request)

north axial pole tilts towards the sun, the sun’s rays have less insulating atmosphere to filter them, and the northern hemisphere warms up. In the northern winter, the north pole tilts

Northern Winter (same famous artist)

Northern Winter (same famous artist)

away from the sun whose warming rays now must penetrate more atmosphere, and the northern hemisphere cools down.  Seasons are opposite south of the equator.  The closer you are to the equator, the more equal are day and night, summer and winter, warmth and cold.  The temperature extremes of winter and summer are replaced by rainy and dry seasons.

At equinox: right diagram shows earth in distance over top of sun

At equinox: right diagram shows view past top of sun towards earth.

Eastern Sunrise, Western Sunset
Throughout the northern winter and spring, the points of sunrise and sunset move farther and farther north.  The extremes are the Winter Solstice (around December 21), when the sun rises and sets farthest to the south, and the Summer Solstice (around June 21) when they are farthest to the north.  The equinoxes mark the halfway point, when sunrise and sunset are exactly east and west.  Well, not exactly.

Using this site, calculating for Santa Monica City Hall (34:00:43° North, -118:29:30° West) on 9/23/15 the sun is exactly at 0° elevation (on the eastern horizon) at 6:43:55 AM, and at 89.71°, slightly north of exactly east. Sunset, when again the sun’s elevation is 0°, is at 6:48:15 PM, and the sun is at 270.04°, again slightly north of exactly west.

If you’ve read this far, you may have noticed that these sunrise and sunset times are a bit slippery, shifting around by 1-2 minutes for what appears to be the same location. The problem is the location isn’t exactly the same. Some locations used are downtown L.A., some are Santa Monica. While both locations have the same clock time, sunrise time changes. Because the earth’s diameter is 24,901 miles, a point on the equator moves 1038 miles per hour, and 17.3 miles per minute. Now invert that. Move 17.3 miles westward from one place, and the sun will rise 1 minute later. Of course, the speed of rotation declines as you move towards the poles; exactly at the poles you don’t move eastward at all. Rotational speed calculations get complicated, but the bottom line is that the sun does rise and set later in Santa Monica than it does in downtown L.A.

So make sure you run outside at 1:22 AM – or thereabouts – on September 23 to witness the autumnal equinox, despite the fact that at that very moment the sun will be undergoing a total eclipse by the earth (aka nighttime), so there really won’t be much to look at for anyone in California. It will be quiet. Probably. By the way – the sun doesn’t rise and set. The earth revolves on its axis. But you knew that.

Autumnal Festivals
The farther one lives from the equator, the more noticeable are seasonal variations in daylight and warmth, and the more important seasonal events such as autumnal festivals become. Most autumn festivals are closely linked to the harvest of crops.

The Snake of Sunlight Main pyramid, Chichen Itza, Yucatan, Mexico

The Snake of Sunlight, main pyramid, Chichen Itza, Yucatan, Mexico
(CostinT from Timeanddate.com)

China and Vietnam celebrate the Mid-Autumn Festival, also known as the Moon or Mooncake Festival, held within 15 days of the Autumnal equinox, during the full moon of early September to early October (Chinese 8th month). Mooncakes are round pastries filled with red bean or lotus seed paste, sometimes containing yolks from salted duck eggs. This is basically a harvest and thanksgiving festival. India has dozens of harvest festivals, not all in autumn. Iran celebrates Mehrgan on October 2 (Gregorian Calendar), a modern form of an ancient Persian Zoroastrian harvest feast. Bavaria’s Oktoberfest, held mid-September to early October, dates back only to 1810 and was originally a celebration for the upcoming marriage of Crown Prince Ludvig (later Ludvig I, the Mad King of Bavaria)  to Princess Therese of Saxe-Hildburghausen. Canadian Thanksgiving always falls on the 2nd Monday of October.

The Celts of Ireland-Britain-France celebrated (and Wiccans still do on Sept. 21st) Mabon, or the Second Harvest when acorns, fallen from the oaks, are planted in fertile soil. It was traditional for a young maiden to cut the last sheaf of harvest wheat. Mabon links – through the usual Christian co-opting of earlier pagan festivals – to Michaelmas, celebrating the slaying of the dragon (aka Lucifer) by Archangel Michael, held on September 29, which signals the official end of the harvest season, and the collecting of the accounts by the Lord of the Manor.

This year we get a special treat – an apocalyptic event on the autumnal equinox. Yes! The world ends yet again. This time around it’s the Apostasy – the Great Falling Away. This event must take place before the Rapture – yes, that rapture – and some Very Wise People, by means of calculations beyond the ken of the likes of us, have determined that this is the date. The apostasy, as best as we here at SMBAS Blog Central can determine, is when sinners reject what little faith they have. The end comes, as you may have expected, by means of a comet plowing into the earth and causing tsunamis and earthquakes. So…eat early and stay out late to watch the comet arrive.  [Chuck Almdale]

Interesting Links
TimeandDate.com – September Equinox
TimeandDate.com – Los Angeles sunrise, sunset & day length for Sep. 2015
TimeandDate.com – Day and Night map for September Equinox 2015
Heliophysics – A Universal Science
Los Angeles Equinoxes and solstices from 2010–2020

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