This is the Classical Astronomy Update, an email newsletter especially
for Christian homeschool families (though everyone is welcome!) Please feel free to share this with any interested friends.
Praise ye him, all his angels: praise ye him, all his hosts. Praise ye him, sun and moon: praise him, all ye stars of light. Praise him, ye heavens of heavens, and ye waters that be above the heavens. -- Psalm 148:2-4 IN THIS UPDATE Autumnal Skies Annular and Total Eclipses Hello Friends, There are two topics in this newsletter so we'll get right to it. I used to always have multiple topics but then the kind and friendly readers explained that it was too much to read. But sky events don't spread themselves out to fit our human schedules. Sometimes there's
nothing to write about, other times there's too much to say. This is one of those time. But I didn't want to let either of these subject pass by, hope this is not too much. I'm especially pleased with the animated videos to help explain about the causes of eclipses and what you can expect to
see during a total solar eclipse. - Eclipses Explained -- An animated basic primer on the
differences between partial, annular and total solar eclipses.
- The Eclipse Experience -- An animated walkthrough of a total solar eclipse, including visual depictions of all the phenomena that one might expect to
see.
- Eclipse Misconceptions -- A lighthearted look at five of the common “urban legends” that circulate about eclipses. MUST SEE!!! MUST SHARE! FUNNY!
- Eclipse Over Ohio - An animated step-by-step depiction of the path of totality across the State of Ohio, including detailed explanations of why eclipse viewing differs with location in the Buckeye State (partial vs. total, different durations of totality
across the path). This video is important to help Ohioans understand why Akron, Cleveland, Dayton and Toledo will experience totality and why Canton, Cincinnati, Columbus and Youngstown will not, and why everyone should get onto the path, the further, the longer.
For more information about topics from Classical Astronomy discussed in this newsletter, please check out a homeschool astronomy curriculum (but popular with adult readers too!) Visit our archive of previous editions of the Classical Astronomy Update newsletters, going back to 2007. ***** Autumnal Skies I got a nice email from Sophie who writes: hi Jay!
greetings from Ireland 🇮🇪
really enjoying your newsletters!
hope you’re doing well.
I’ve noticed over the last few months that the moon seems to be much lower than usual in the sky, clinging to the southern
horizon even many hours after rising. would you have any ideas why this happening, or is this a seasonal thing that I haven’t noticed before?
thanks a lot and God bless!
I really like getting questions like this, especially about things the
readers are seeing in the sky. It's encouraging to know that the readers are outside, looking up, and noticing things that seem odd. Some of the best newsletters have been written in response to reader questions. So thanks, Sophie! Yes, it’s a seasonal thing, but you have a good eye, most people never give such things a second thought.
During evenings in late summer and fall, the Summer Triangle is high overhead, which is the part of the sky including the constellation Sagittarius, which hosts the cardinal point of the winter solstice. This point in the sky is low in the skies of the northern temperate latitudes. Sagittarius grazes the treetops here in Cleveland
(latitude 42 degrees north). It's even lower in the skies of Ireland, whose latitudes span 10-15 degrees further north (50-55 degrees north latitudes). Around the time of the autumnal equinox (just past a couple weeks ago), the First Quarter Moon (i.e., the waxing half-moon) passed through the point of the winter solstice in Sagittarius during the autumn evenings, and thus appears very low in the evening sky. Sagittarius is the constellation which will be aligned with the Sun in the next season (i.e. on the first day of winter). So the Moon in Sagittarius can give us a "sneak preview" of the Sun's position on the shortest day of the year, a couple months from now. As explained in our Signs & Seasons curriculum, the circle of the ecliptic in the sky corresponds to the plane of the Earth's orbit. Since the Earth's axis is tilted compared to the ecliptic plane, the annual path of the Sun through the sky appears slanted compared to the celestial equator. In fall evenings after sunset, this slant causes the Moon to remain close to the horizon during waxing phases, resulting in the "Harvest Moon" effect, as explained in previous newsletters.
The opposite situation prevails during autumn mornings before sunrise. The sky has rotated over the span of nightime so that the low-riding sky around Sagittarius has set. The sky featuring Orion the Hunter has risen overnight to be high in the sky before
sunrise. In this portion of the sky, the circle of the ecliptic is slanted at a steep angle to the horizon, which is the opposite situation in autumn mornings compared to autumn evenings. So in the mornings of autumn, before sunrise, you can see the waning phases of the Moon high in the sky, sailing above Orion. Look for the Last Quarter -- the waning half-moon -- on Friday, October 6. This will be a beautiful scene as the stars near Orion,
which are among the brightest visible stars, will share the pre-dawn sky with the brilliant planets Jupiter and Venus. The waning crescent Moon will align with Venus on the morning of Tuesday, October 10, which is always a breathtaking sight. So if you're up early walking the dog on these crisp, cool fall mornings, be sure to notice these glittering celestial bodies. Annular and Total
Eclipses As you've heard, we'll be having an annular eclipse on October 14, 2023 and a total solar eclipse on April 8, 2024. So what do these terms mean? And why are we having the one six months
before the other? The answers are due to the elegant celestial order caused by the gravitational interaction of the Sun, Moon and Earth. Let's begin by explaining that the orbits of the Earth, Moon and planets all have orbital
elements which describe the orientation and physical features of the motion of the body around the larger body which it orbits. For the purpose of this discussion, we'll only discuss the following: i is the
inclination of the Moon's orbit, the angle with which the lunar orbital plane is tilted to the ecliptic, the plane of the Earth's orbit. Ω (big omega) is the longitude of the ascending node,
which is the position in the sky of one of the Moon's "nodes" which are the points where the Moon's orbit crosses the ecliptic plane. ω (small omega) is argument of perigee, which is the position
in the sky where the Moon's orbit is closest to the Earth. Don't worry, we wont be spending too much time with all these symbols! All we need to know about the inclination i and the ascending
node Ω is that since the Moon's orbit is tilted, eclipses can only occur when the Moon is close to a node. This only happens twice a year, during eclipse seasons. There is always at least one solar and lunar eclipse in each eclipse season, and these eclipse seasons occur on opposite times of the year. So this is why we'll have one type of solar eclipse in October and then another type the next April. The Moon passes its point of perigee ω each lunar month and is then closest to the Earth. The Moon passes the point of apogee at the opposite point of the lunar month, when the Moon is farthest from the Earth.
When it is at perigee, the Moon appears largest in the sky. Conversely, at apogee, the Moon appears smallest. The Moon appears about 16% larger at perigee than
apogee. There is a similar difference with the size of the Sun at perihelion, when the Earth is closest in January, and aphelion, when it is furthest away in July. However, this difference in solar size is only about 3%. The media has latched onto this concept by constantly mentioning a "Supermoon" whenever a Full Moon is near perigee. As mentioned over the years in this newsletter, this idea is so airheaded because that 16% is impossible to judge by eye. You'd have remember
what the Moon looked like from a previous month and compare. I've been looking all these years and I can't discern any size difference, though sometimes a so-called "Supermoon" appears brighter, maybe due to the power of suggestion. On one hand, I find the term "Supermoon" annoying since the Latin root "super" means "over" or "above." By that actual definition, the term should properly apply to lunar apogee, when the Moon is furthest away. But the media then further gunks things up by calling an apogean Full Moon a "minimoon" or "micromoon." I try to hold out for consistency in Latin etymology by calling an apogean Full Moon an "Inframoon" where "infra" is the opposite of "super,"
meaning "under" or "below." The term "Supermoon" entered the media vocabulary in 2011 following the tsunami which provoked the disaster at the Fukishima nuclear plant in Japan. Some astrologer (not a scientist but a purveyor of
nonsense) invented the term by speculating that the purported larger gravity of a perigean "Supermoon" caused the earthquake which produced the tsunami. This was dismissed as rubbish by the scientific community, otherwise there would be similar earthquakes every month, which there are not. But the airheaded "Supermoon" label has stuck in the airheaded media, and now we all have to live with it. But on the other hand, looking on the bright side, I'm at least glad that the word might
get some people outside looking at the sky. So anyway, a solar eclipse happens whenever the New Moon lines up with one of the lunar nodes during an eclipse season (as shown in our video, Eclipses Explained.) But the type of solar eclipse depends on whether the Moon is closer to apogee or perigee. When the Moon is closer to apogee, an annular eclipse occurs since the Moon's umbra does not reach the Earth. As depicted in the image above,
the visual size of the Moon is smaller than the visual size of the Moon, resulting in a ring of bright sunlight since the Sun is not completely covered by the Moon. Conversely, when the Moon is closer to perigee, a total solar eclipse occurs since the lunar umbra reaches down to the surface of the Earth. As also depicted in
the image above, the visual size of the Moon is larger than that of the Sun, so the Sun is completely covered by the lunar disc, and hence totality. The media informed us all of a "Blue Supermoon" in the month of August. A "Blue Moon" has lately been defined as the second occurrence of a Full Moon in a
calendar month. And when both Full Moons are near perigee, they're both "Supermoons." In other words, a they are both non-events, nothing especially noteworthy to see. This happened in August, 2023, with perigean Full Moons occurring on August 1 and August 31. The next month the same media proudly proclaimed that another Supermoon occurred on September 29, and that this would be the last of 2023. Notice from the figure below that the points of perigee and apogee stay in the same general positions from month to month, but that the point of the Full Moon shifts compared to the point of perigee. For this reason, the next Full Moon after September 29 would not be close enough to
perigee, hence no "Supermoon." Also, when the New Moon aligns again with the node on October 14, it'll be on the opposite side of the Moon's orbit, closer to the point of apogee. Thus, it'll be an annular eclipse since the New Moon is closer to apogee and therefore too far away so that the umbra does not reach the Earth. As explained in the last
newsletter, celestial objects tend to remain aligned in the same orientation as they move through space. In the given example, the Earth's axis always remains pointed at the North Star throughout the year and does not change with the Earth's orbital motion. This is because of inertia, as explained by Isaac Newton. Objects in space tend to remain aligned in their same orientations unless something moves
them. The same is true with the orbit of the Moon. The lunar nodes and the points of perigee and apogee tend to stay aligned in the same general direction. However, just as the gravity of the Moon slightly tugs on
the Earth's axis, causing precession, the orbital elements also shift slowly over time because of the gravitational forces acting on the Moon. The masses of the Earth and Moon are in proportion of the Earth being like a bowling
ball and the Moon being like a wiffle ball. The Sun's gravitational force on the Moon is about 20% of the Earth's so the Sun is like 1/5 of a bowling ball to the Moon. So anyway, the lunar wiffle ball is in a constant "tug of war" between the larger forces of the Earth and Sun. And because of this, the nodes and perigee are constantly being deflected by gravity. As a result, the nodes are constantly being rotated 20 degrees toward the west each year, while the perigee is turning 40 degrees to the east annually. This is only a minor amount of shift from month to month, but it adds up over a span of years. Long story short, since the solar eclipse of October 14 is annular, the points of perigee and apogee will still be aligned in a similar general direction during the next eclipse season on April 8. So by then the New Moon will line up with perigee, so that the perigean New Moon casts
the umbra upon the Earth in the total solar eclipse over the United States. And yeah, you guessed it, a similar alignment of perigee will still prevail in the next eclipse season after that, when there will be
another annular eclipse over the Pacific Ocean on October 2, 2024. For this reason, there is a basic patten to solar eclipses where totals alternate with annulars in alternating eclipse seasons. This is not a strict rule since there are other factors involved in the eclipse cycles. And though annulars are not as famous, they are actually more numerous than totals. Anyway, the subject of "eclipse periodicities" is very fascinating, and is my greatest interest in eclipse astronomy. However, this subject is quite deep and will probably never be delved into in this newsletter. Hoping to treat this subject in Book 4 of the series beginning with Signs & Seasons, if I live long enough and if Jesus does not return first! Hope all of you are able to SAFELY view the upcoming annular eclipse, and I hope the above explanation was clear enough to help you understand the connection between Supermoons, annular eclipses and total solar eclipses. Till next time, God bless and clear skies, - jay The Ryan Family Cleveland, Ohio, USA When I consider thy heavens, the work of thy fingers, the moon and the stars, which thou hast ordained, what is man that thou art mindful of him? and the son of man, that thou visitest him? - Psalm 8:3-4, a Psalm of David
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