As the evenings draw in, the Full Moon is a beautiful and accessible stargazing object. As is the case in the Spring, many cultures have festivals during the Fall that are set by the Lunar Calendar, and so they are explicitly or implicitly tied to the Autumnal Moons. For example, the date of Rosh Hashanah/Yom Kippur is set by the “lunisolar” Hebrew calendar, which means it (usually) starts on the date of the closest New Moon to the Autumnal Equinox (the date when night and day have equal lengths). Another example is the Mid-Autumn Moon festival — a very important date in many East and Southeast Asian cultures, which coincides with one of the Full Moons in the Fall. This year, it is the September 20th Full Moon.
Observant stargazers will notice the Moon is not up at night all the time. The Full Moon is specially accessible, as it is directly across the sky from the Sun, and therefore rises as the sun sets, making it a bright early evening object. Often the Full Moon appears to be incredibly large as it rises above the horizon. This phenomenon is known as “the Moon Illusion” and is a trick your brain plays as it processes visual information. The Moon is not actually any larger near the horizon, but it will often appear redder, as more of its blue light is scattered by the atmosphere.
Over the course of the month, the Moon moves closer to the Sun, until a New Moon happens when the Moon is in the same part of the sky as the Sun, and therefore both invisible and only in the sky during the hours of daylight. Sometimes the Moon passes precisely in front of the Sun, causing a solar eclipse — one of these solar eclipses will be visible from parts of Antarctica in early December.
Another type of eclipse is a “Lunar Eclipse” when the Earth passes between the (Full) Moon and the Sun. There will be a partial lunar eclipse visible from right here at Haverford very early in the morning of November 19th. During this event, the Moon may not completely disappear, but will take on a distinct red tinge, as most of the light from the Sun is blocked by the Earth. No special equipment is needed to view this event, which will look nice with the unaided eye.
If you have trouble keeping the types of eclipses straight, Astronomer Katie Mack created this helpful diagram, which went viral a few years ago on Twitter.
Finally, Venus, as the “evening star” deserves a mention for stargazing this Fall. In late October it will reach its farthest apparent westerly distance (known technically as Western Elongation) from the Sun, making it a bright and beautiful point of light in the South Western evening skies. It should not be confused with the bright planet Jupiter (and the slightly dimmer Saturn) which are currently high in the South Eastern skies in the evening, and will appear to move closer and closer to Venus in the sky as the semester progresses (mostly because of the Earth moving in its orbit). All of these objects look great through our campus telescopes, and we hope you will be able to visit soon to look at them, but meanwhile enjoy the sites with your unaided eye.
Fall 2021 Stargazing Diary
September
20th: Full Harvest Moon
22nd: Autumnal Equinox (3.21pm ET). This is the time at which the Earth reaches the point in its orbit where night and day have equal lengths.
23rd: See a nearly Full Moon near Uranus
October
20th: Hunters Moon (A traditional name for the Full Moon in October)
25th: Mercury at greatest elongation (further from the Sun) in the morning sky
29th: Venus at greatest elongation (furthest from the Sun) in the evening sky
November
7th: Clocks “Fall” back, ending Daylight savings time.
17/18th: Leonids Meteor Shower
19th: Partial Lunar Eclipse (2.18-5.47am) and “Micro” Full Moon (the opposite of a “Super” Full Moon)
December
4th: Total Solar Eclipse visible from Antarctica (and online!).
13-14th: Geminids Meteor Shower
19th: Full Moon
21st: Winter Solstice (10.59am ET). The longest night of the year in the Northern hemisphere.
This article was edited by Emi Krishnamurthy and Anagha Aneesh.