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Classical Astronomy Update, an email newsletter especially
for Christian homeschool families (though everyone is welcome!) Please feel free to share this with any interested
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Thus saith God the Lord, he that created the heavens, and stretched them out; he that spread forth the earth, and that which cometh out of it; he that giveth breath unto the people upon it, and spirit to them that walk therein: I the Lord have called thee in righteousness, and will hold thine hand, and will keep thee, and give thee for a covenant of the people, for a light of the Gentiles. -- Isaiah 42:5-6 IN THIS UPDATE A Year of Occultations Hello Friends, I used to always enjoy winter. I used to ski and loved the feeling of a bracing wind on my face. But I enjoy winter less
and less as I get older. This particular winter has been blah. Lots of gloomy clouds and mostly unlpeasant weather -- either too cold or too warm, wet and muddy. I'm glad that the days are getting longer and am eager for the warm season ahead. My goal for 2023 is to cycle the Ohio to Erie Trail from Cleveland to Cincinnati, and join The 326 Club, peddling the entire length in a single outing. So I can't wait for spring! Thanks for the remarks about Substack. The comments were mostly negative, which is fine, I have enough things to do without adding one more. Still, I would like to blog on more subjects than just astronomy and
reach out to a broader readership, so I am still considering starting an account. If I do decide to start a Substack, rest assured that I'll still double post to this newsletter and keep it going for the foreseeable future. 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. *****
A Year of Occultations As reported in this previous newsletter, there was a lunar occultation of Mars on December 8. We were clouded out here in Cleveland, as is normal for this time of year. But I did get a nice email from Jacob in Texas who
wrote: Thank you for sending this timely email update. I did not realize this event was happening, but armed with your alert I was able to get a few good pics before scattered cloud cover obscured my location in Cedar Park,
TX. Picture snapped with my Google Pixel smartphone through a pair of 135mm binoculars, amazing how little it takes to get lunar details to pop out even with a low-tech setup. Wow, that's close! If you were viewing it live and "in person," Mars would be appear conspicuous than in this image. The optics in
cameras are very crude compared to the miracle of the human eye, which is a far more sophisticated piece of optical engineering than a mere man-made camera. The human eye can detect light differences over a factor of a trillion, from full noon summer sunlight down to faint rural starlight. This is yet another way of how we are "fearfully and wonderfully made." So when you're looking at this next lunar occultation, you'll see that the Moon's bright light does not swamp out the lesser
light of Mars, which is itself very bright compared to the stars. Jacob was a student of our Signs & Seasons astronomy curriculum back in his school days and is currently working in the aerospace industry. Thanks for writing, Jacob! S&S has been out for over 15 years, so all the early students of this course are now grown up and currently pursuing careers. If you're
also an S&S alum, please drop a line and let us know what you're doing. There was another lunar occultation of Mars back on January 3, but that was only visible from Africa and not visible from the USA. But this
next one will again favor the USA, so 2 out of 3 ain't bad! This occultation will only be visible from the southern states, and will miss the northern states, vice versa from last time. This proves once again how, in astronomy, what goes around comes around. 2023 will be a banner year for lunar occultations visible from the USA. Here's the objects that American can see occulted by the Moon in '23, with dates:
May 17 -- Jupiter Aug 25 -- Antares Sep 16 -- Mars Nov 14 -- Antares I'll hopefully get a newsletter out for some of those
events with more details. For these and any other lunar occultations, check out this website of the International Occultation Timing Association (IOTA). There will be a season of monthly lunar occultations with the star Antares in Scorpius running from August, 2023 through June, 2024. Occultation seasons are interesting phenomena that I'd like to explain in a future newsletter. There are several bright first magnitude stars close
to the ecliptic that are regularly occulted by the Moon whenever a node of the Moon's orbit is sufficiently close. There is an 18.6 cycle of the Moon's nodes and there are two occultation seasons per cycle, or one about every 9 years. An occultation season results as the node passes close to the star, so that a lunar occultation occurs once every sidereal month, which is a lunar cycle of 27.3 days. This topic is too involved to quickly explain here, but will be explained
in detail in Measuring the Heavens, the upcoming sequel to our Signs & Seasons astronomy curriculum. Occultations are similar in principle to a total solar eclipse, in which the Sun is covered over by the Moon, blocking the Sun's rays for a time, so that the shadow of the Moon is cast upon an area of the Earth. A lunar occultation is a type of eclipse in which a star or planet is covered over by the Moon, blocking its
light over an area of the Earth for a period of time. The next lunar occultation of Mars will be visible from the USA on the evening of Monday, January 30 or after midnight on Tuesday, January 31, depending
on your location. This event will favor the southwestern USA, where it will be visible at an earlier time. Check out the previous newsletter for
basic details about lunar occultations. The Moon is always moving against the stars at a rate of 12 degrees per day, which is the same as 1 lunar diameter per hour. As the time of occultation approaches, the Moon
draws closer and closer to Mars and eventually covers over the Red Planet. The moment of occultation will be easier to observe for the January 30 event than the last one back on December 8. At that time the Moon
was full, but this time the Moon will be in a waxing gibbous phase so that the dark limb of the Moon will first contact Mars, being more readily visible. At any given moment during the event, the occultation is visible from an area on the Earth corresponding to the shadow of the Moon blocking the rays
of light emanating from Mars. This shadow area is the same size and shape as the Moon, a large circular footprint about 2000 miles in diameter. This circular footprint of the Moon's shadow area moves from west to east upon the Earth, corresponding to the Moon's eastward orbital motion.
Since the Moon is 2000 miles in diameter, and since it moves 1 diameter an hour in its orbit, the area of occultation moves at a speed of 2000 miles per hour across the Earth. So it takes 1 hour for the occultation area to pass , and this is the longest possible duration as seen from locations along the widest width of this area. The area of occultation of the January 30 event
follows a path that comes off the Pacific Ocean and first makes landfall on the west coast of the USA. Thus, the occultation is visible at the earliest hour of Universal Time as seen from out west. The area of occultation then moves east across the southern USA and over Central America heading toward the Atlantic Ocean. For this reason the occultation begins at a later hour of Universal Time as seen from back east, time zones notwithstanding. You can find the local times of disappearance and reappearance of Mars for your location from this website. Remember that the times are given in Universal Time (UT) which is the same at Greenwhich Mean Time (GMT), 5 hours ahead of Eastern Standard Time (EST) and additional hours ahead of Central, Mountain and Pacific Standard Time. The graze line of the occultation is the boundary of visibility. For this event, the occultation is visible for all USA locations to the south of the graze line. But the occultation will not be seen for American locations to the north. Points directly along the graze line will see the limb of the Moon momentarily graze Mars at its closest.
This sight in itself would be very interesting. As shown in the figure below, the graze line extends from just south of Montery Bay, California to just south of Savannah, Georgia. For locations of visibility south of the graze line,
this occultation will be very short since only the northernmost portion of the Moon will briefly cover over Mars. Everywhere north of the graze line will see a very close lunar conjunction with Mars, a separation of only a small fraction of a lunar diameter. So you'll see an interesting sight wherever you live in the USA so be sure to go outside and take a look! I haven't had a chance to continue debunking flat earth-ism, but lunar occultations are another thing that disproves some of the tenets of this belief. Flat earth-ism declares that the Moon is only a tiny sphere 32 miles in diameter and a mere 3000 miles above the flat disc of the Earth. But there is no way that such a miniscule lunar
globe could leave a 2000 mile diameter footprint upon the Earth. Moreover, such a close Moon would suffer from a considerable amount of parallax compared to Mars and the background stars, which is a fatal flaw that disproves flat earth-ism. The subject of parallax is too long to explain here, and maybe someday I will muster the enthusiasm to continue debunking flat earth-ism. But in any event, keep in mind that flat earthers are undeterred by facts and are well-armed with convenient talk-around explanations for any observations that support the standard model of the Earth, Moon and solar system. Anyway, if you observe this occultation or a close conjunction of Mars, please drop a line to describe your experience. Til 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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