THE SOUTHWORTH PLANETARIUM 70 Falmouth Street Portland, Maine 04103 (207) 780-4249 usm.maine.edu/planet 43.6667° N 70.2667° W Founded January 1970 2022-2023: XVIII Sunrise: 6:28 a.m. Sunset: 6:38 p.m. Civil twilight ends: 7:07 p.m. Sun's host constellation: Virgo the Maiden Moon phase: Waning crescent (11% illuminated) Moonrise: 3:44 a.m. (9/23/2022) Moonset: 6:05 p.m. (9/23/2022) Julian date: 2459845.16 "Are modern folk, perhaps, afraid of the night? Do they fear that vast serenity, the mystery of infinite space, the austerity of the stars? Having made themselves at home in a civilization obsessed with power, which explains its whole world in terms of energy, do they fear at night for their dull acquiescence and the pattern of their beliefs? Be the answer what it will, to-day’s civilization is full of people who have not the slightest notion of the character or the poetry of night, who have never even seen night. Yet to live thus, to know only artificial night, is as absurd and evil as to know only artificial day" -Henry Beston THE DAILY ASTRONOMER Thursday, September 22, 2022 Questions about Autumn Happy Autumnal Equinox! No, that is certainly not an oxymoronic statement. Autumn has much to recommend it. That quintessential New Englander Nathaniel Hawthorne once said "I cannot endure to waste anything so precious as autumnal sunshine by staying in the house." Vincent Van Gogh, with the hyper sensitivity particular to artists, lamented, "As long as autumn lasts, I shall not have hands, canvas and colors enough to paint the beautiful things I see." Although the sight of frost-tipped leaves resting atop browning grass might engender a profound sense of loss and decay to some, Emily Bronte perceived it differently. "Every leaf speaks bliss to me, fluttering from the autumn tree." Lucy Maud Montgomery was delighted to live in a world that contains Octobers, while Ralph Waldo Emerson yearned for nothing more than to sit alone on a pumpkin. Even the iconoclastic Nietzsche described autumn as "more of a season of the soul than of nature." Perhaps those expressed sentiments will serve to assuage the quiet grief one experiences when the fierce summer heat yields to the deepening autumnal chill. Astronomically, autumn's onset is marked simply by Earth's passage through a point in its orbit where neither pole is inclined toward the Sun more than the other. This equality of inclination occurs only twice a year: during the vernal equinox and autumnal equinox, the first day of spring and fall, respectively. The vibrant foliage, reduced temperatures, hardening soil and crop deteriorations are merely Earth's reactions to the Sun's decreasing altitude. Today, we commemorate autumn's arrival by answering some of the common questions the equinox raises. *Does the Sun actually only rise due east and set due west on the first day of spring and autumn?* Yes. Each day the Sun rises above the eastern horizon. However, only on the vernal and autumnal equinoxes will it rise due east. Each day after the autumnal equinox, the Sun rises progressively farther south until it reaches its extreme southeast position on the winter solstice. Conversely, after the vernal equinox, the Sun rises progressively farther north until it reaches the extreme northeast position on the summer solstice. [image: HorizonPos.jpg] The Sun rises due east only on the vernal and autumnal equinoxes. During the spring and summer, it rises north of east. During the autumn and winter, the Sun rises south of east. *Can I balance an egg on its end today?* Well, yes, you can. Of course, you can balance an egg on its end on any given day provided you possess vast reserves of patience and an immense amount of time. The notion that eggs can only balance on their ends during the equinox is totally false. It is also likely predicated on the belief that Earth is actually upright on these two dates. It isn't. Earth's inclination angle, or *obliquity*, remains constant throughout the year.* [image: 6-40.jpg] One can balance an egg on its end on any day of the year, provided one is patient and very careful*.* *Why doesn't the autumnal equinox occur on the same date/time each year?* Simply because Earth's year is not equal to an integer number of days. Earth requires approximately 365.2422 days to complete one revolution around the Sun. For this reason, we need to insert a leap day into the calendar every four years.** Generally, an autumnal equinox will occur about six hours later than the previous one. Let's look at the next few autumnal equinox dates (Eastern Time Zone): - September 22, 2022 9:04 p.m. - September 23, 2023 2:50 a.m. - September 22, 2024 8:43 a.m. - September 22, 2025 2:19 p.m. - September 22, 2026 8:05 p.m. - September 23, 2027 2:01 a.m. - September 22, 2028 7:45 a.m. One will notice the nearly six hour separation between the equinox date/times except on leap years, when it occurs about 18 hours earlier. The difference isn't exactly six hours because the year isn't exactly 365.25 days long. Just as an exercise, can you estimate the date/time of the 2029 autumnal equinox? See the actual date.*** *Tonight autumn will begin in the northern hemisphere while spring begins in the southern hemisphere. What season will it be at the poles and on the equator?* Autumn will begin at the North Pole and spring will begin at the South Pole tonight. As the equator is a line of no thickness, it means no sense to specify its season. Instead, one would say that it is autumn north of the equator and spring south of it. If you stood along the equator, one side of your body would be in autumn, the other in spring. *Will it now become dark at the north pole?* Not straight away. In fact, due to atmospheric refraction effects, the Sun will remain in the sky at the north pole for a few days after the autumnal equinox. Then, the north pole will experience 24 hour civil twilight until October 9; 24 hour nautical twilight until October 20th. At that time, it will become quite dark. However, the last twilight phase, astronomical, will not end until around November 6th. Astronomical twilight will then begin at the north pole at the end of January. [Note: due to those same atmospheric refraction effects, the Sun appeared above the South Pole horizon earlier this week.] Tonight, at precisely 9:04 p.m. summer 2022 will pass into the ages as autumn 2022 draws its first breaths. Again, do not despair, as was once said long ago by a writer now known only as anonymous, "Autumn shows us how beautiful it is to let things go." *It does change over longer periods of time, but we'll ignore that fact for the moment. **Except for century years, unless those century years are multiples of 400. The year 1600 was the first leap century year to occur after the Gregorian calendar reform in 1582. The year 2000 was the second; the year 2400 will be the third. ***September 22, 2029 1:37 p.m. To subscribe or unsubscribe from the Daily Astronomer: https://lists.maine.edu/cgi-bin/wa?SUBED1=DAILY-ASTRONOMER&A= <https://lists.maine.edu/cgi-bin/wa?SUBED1=DAILY-ASTRONOMER&A=1>