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.
Then Paul stood in the midst of Mars' hill, and said, Ye men of Athens, I
perceive that in all things ye are too superstitious. For as I passed by, and beheld your devotions, I found an altar with this inscription,
To The Unknown God. Whom therefore ye ignorantly
worship, him declare I unto you. - Acts
17:22-23
IN THIS UPDATE
Three Planets in a Row
Closest Opposition of Mars
Eclipse Duo
Hello Friends,
There's lots of sky news to report. All five of the classical planets are currently in the evening sky. While Mercury is always elusive under even the best circumstances, you can easily spot the other planets this summer... Venus, Jupiter,
Saturn and Mars.
The summer of 2018 is be a good time for observing most of the visible planets. You can begin your observing program with our Signs & Seasons astronomy curriculum.
We are still continuing our offer -- if you order Signs & Seasons and/or the workbook, we'll throw in a FREE copy
of Moonfinder, a children's storybook for learning the monthly cycle of the Moon's phases. This offer is not posted on our website, but it will be honored just the same. And if you order Moonfinder directly, we'll throw in a second copy to share with a friend.
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.
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Three Planets in a Row
If you follow our Facebook Page, you might have seen the info-graphic meme posted last week about the Moon aligning with Mercury and Venus. The image below shows the sight from last weekend. Such lunar-planetary conjunctions are very common, and happen every month as the Moon follows its course through the zodiac constellations. These lunar-planetary conjunctions are interesting sights in the night sky, worthy of a couple minutes of our time to stop and notice. Yet for whatever reason,
these commonplace celestial alignments are not usually discussed or mentioned in the media. Many people are unaware that the planets are even visible and that they frequently line up with the Moon.
Since last week, the Moon has continued in its orbit, and is now considerably further to the east. But on the evening of Friday, July 20, the waxing gibbous Moon will align with the bright planet
Jupiter, which has been blazing all summer in the southern sky in the early evening after sunset.
In 2018, Jupiter has been passing through the stars of Libra, the Scales. Libra is not much of a constellation, mainly formed of a few faint stars, only two of which are readily visible.
Both have "official" names that are polysyllabic and practically unpronounceable. But you can conveniently think of them as "The Northern Claw" and "The Southern Claw." This is because, in ancient times, the stars of Libra were considered to be the "Claws" of the nearby Scorpius, the Scorpion. The constellation Libra was recognized by the decree of Caesar Augustus, the same Roman emperor who ordered the census in the Nativity story of Jesus.
Anyway. Jupiter has been lined up with "The Southern Claw" of Libra during 2018. Look for the Moon to pass this pair on Friday evening.
The Moon will continue to move east after that, passing over the stars of Scorpius and toward Sagittarius. This summer, Saturn is near the "dome" of the "teapot" asterism in Sagittarius. Try to learn to identify
this teapot shape on clear nights this summer, and also the distinctive shape of the Scorpion nearby. The Moon aligns with Saturn on the evening of Tuesday, July 24.
Keep following the Moon's cycle of phases for the rest
of the week. The Full Moon is in conjunction with Mars on the evening of Friday, July 27, and this alignment occurs in the constellation Capricornus.
This is a very special conjunction of the Moon and Mars.
For one thing, the night of the conjunction is the same night as the opposition of Mars. At this time, Mars is in a line with the Earth and the Sun, and Mars is at about its closest distance from the Earth. At opposition, Mars is "opposite" the position of the Sun in the sky. Thus, Mars rises in the southeast at the same time when the Sun sets in the northwest. For more about oppositions and the motions of the Sun and planets, check out our
Signs & Seasons astronomy curriculum.
At the same time as the opposition-conjunction, the
Moon will also be undergoing a total lunar eclipse! But this happens to be the longest lunar eclipse of the 21st century, 1 hour and 43 minutes! And 2018 is the closest opposition of Mars in nearly a 50 year span. These two factors combine to make this opposition-conjunction-eclipse just about the rarest of rare sights that can ever be seen in the sky... a "bloody" Moon sharing the sky for a long time with a "bloody" planet of nearly maximum
brightness.
This will be a spectacular sight for those fortunate enough to see it. However, the bad news for Americans is that we will not see it from home. While some portion of this eclipse will be visible from most areas of the planet, no phase of the eclipse will be seen from anywhere in North
America. See the eclipse news segment later in the newsletter for a map and additional details. The eclipse will most closely favor the Middle East and India, but all of Eurasia, Africa and Australia will see most of the eclipse.
If you know any missionaries in any of these parts of
the world, please share this newsletter with them so that they can see this rare celestial alignment. This can also be a ministry and educational opportunity for them to share with the local people in their mission field.
Click the graphic above to see the Facebook info-graphic meme!
Share with all your friends on social media!
Closest Opposition of Mars
In the summer of 2018, the three visible superior planets are clustering up together in the evening sky -- Jupiter, Saturn and Mars. This is happening because all three planets just so happen to be at places in their orbits on the same side of the Sun, so that they all appear to line up with adjoining constellations. Jupiter and Saturn are slow-moving outer
planets, and these two will draw closer and closer until 2020, sharing the sky for several years to come. Mars orbits more quickly, and just so happens to be "passing through" this part of the sky during 2018.
Because of this clustering, all three planets line up with the Earth and Sun in succession. This lining up is "opposition," when the Earth passes directly between the Sun and the planet, and the three bodies essentially fall along the same line. At opposition, the planet is at the closest point in its orbit to the Earth and thus appears brightest in the sky and largest as seen through a
telescope.
Jupiter was at opposition on May 9, 2018, and was lined up in the sky with the constellation Libra.
After the opposition with Jupiter, the Earth soon swung around its orbit to the place where it aligned with Saturn, at
opposition on June 27, 2018, in the same line of sight as the stars of Sagittarius.
The final opposition of the season will occur on Friday,
July 27, when the Earth moves into alignment with Mars, which shines brightly in the constellation Capricornus. At this time, Mars shines most brightly in the sky and appears largest through a telescope.
The 2018 opposition of Mars is its closest in 15 years. In 2003, Mars had its closest opposition to the Earth in
all human history, calculated to be the nearest pass in over 50,000 years. This closest opposition was widely promoted in the media, and spawned the famous "Mars Hoax" that became an internet nuisance for many years afterwards. That historic opposition was extensively covered here in the
Classical Astronomy Update newsletter. Check out this Update article from 2003, A Brief History of Mars for historical background information and folklore about the "red planet" Mars.
The reason for this closest alignment was that, in 2003, an opposition occurred while Mars was very near the point of perihelion. All the planets, moons and other
orbiting bodies have an elliptical orbit such that they are closer to the Sun at certain times. Perihelion represents the point in a planet's orbit where it makes its closest approach to the Sun. Conversely, aphelion is the point where the planet is furthest from the Sun.
The orbit of Mars is much more elliptical than the Earth. So when an opposition occurs at perihelion, Mars is at its closest possible position to the Earth, and thus at its brightest and largest possible size as can be seen through a telescope.
Mars takes about two years to orbit the Sun. So because of the differences in the orbits of
the Earth and Mars, there is an opposition of Mars about every two years and a couple extra months. Thus, these oppositions occur in a rough cycle that complete a "loop" of the Earth and Mars orbits about every 15 years, about every seven or eight oppositions. Along this loop, some oppositions are nearer to aphelion, where Mars is farther from the Earth. So these oppositions are not as bright, and do not appear so large through a telescope. The last aphelion opposition
was on March 3, 2012.
As can be seen from the figure above, the opposition of 2003 was historic because Mars was very nearly at the precise point
of perihelion, just about the theoretical closest possible proximity to the Earth, and thus the brightest that ever could be seen. The opposition of 2018 occurs a month earlier on the calendar, and therefore is not quite as close or as bright. But this difference is actually quite small in celestial terms.
In both 2003 and 2018, Mars has a stellar magnitude of about -2.8, actually brighter than Jupiter, and at these times is the brightest object in the sky, after Venus. But meanwhile, in 2012, when Mars was near aphelion, its brightness topped out at -1.4, slightly
less than Sirius, the brightest star. This is still quite bright compared to Mars's normal brightness, but at a perihelion opposition Mars is about four times brighter than at an aphelion opposition.
So anyway, the big takeaway is, Mars oppositions are best about every 15 years, and in 2018 Mars is the biggest and brightest it will be until 2035. So this is a great summer to take the kids and visit your local planetarium, astronomy club or observatory to get a telescopic view of Mars. You can find a searchable listing of local groups in
your area at the Clubs & Organizations link at the Sky & Telescope website.
Because of the geometry of the orbits of Earth and Mars, there will be similarly close oppositions of Mars in the decades beyond. While this might not be useful information to the parents, today's kids (and their kids!) can hope to see bright oppositions of Mars in
2050, 2065 and 2082.
If you do visit your local astronomy group, be sure to adjust
your expectations beforehand! Don't expect telescope views to look like Hubble photos! At opposition, the eyepiece can reveal some surface detail on Mars and possibly the ice caps. You have to appreciate how cool it is to even see a planet at all with your own eyes, and not be disappointed that it does not compare to whiz-bang computer processed images. But when Mars is not near opposition, all you can see is a little orange dot, so this summer is your big chance to see
anything of Mars.
The image below gives you an idea of the size differences between perihelion and aphelion oppositions at the same magnification. In 2018, Mars appears about 97% as large as it did in 2003. At the next closest opposition of the 21st century, in 2082, Mars will be at 99.8% of its 2003 size. But in 2010, when Mars was near aphelion, Mars was only 56% of
its 2003 size, quite small and faint in comparison. If you want to see Mars slightly better than 2003, you'll have to hang around until August 29, 2287!
So don't miss this rare chance to observe Mars with your family and friends in the summer of 2018!
Eclipse Duo
This newsletter is running long, so we'll briefly note the unique eclipse season that is also happening this summer. One thing to understand about eclipses is that they always occur in "seasons" that include a solar/lunar pair. Whenever there is a solar eclipse at the New Moon, there is always a lunar eclipse at the Full Moon either before or
after.
The summer of 2018 features a rare eclipse duo. In this situation, there is a partial solar eclipse at one New Moon followed by another
partial solar eclipse at the next New Moon. In a duo, one of the solar eclipses is visible in the Arctic while the other is visible in the Antarctic. A duo does not offer much to see for most of the people in the world since the eclipses are very "shallow." But it's a rare circumstance since it only happens about every nine years.
A duo is a cool idea since one eclipse belongs to a saros series that is old and nearly ready to expire, while the other eclipse belongs to a saros series that is just beginning. It would require a lengthy explanation, but suffice to say briefly that a saros
series is a "family" of 70-some related eclipses, each separated by 18 years, 11.3 days. A complete series extends for around 1300 years, a considerable segment of human history. So the beginnings and endings of such cycles can be considered momentous.
The first eclipse in the duo was on July 13. It was the third last member of Saros 117, which began in the year AD 792. The last eclipse in this series will occur in 2054, after which Saros 117 will expire.
The second eclipse in the duo will be on August 11. This is the sixth member of Saros 155, which began in 1928. This series is calculated to continue until the distant, futuristic year
3190.
Here's the interesting part: eclipse
seasons that include duos include three eclipses total! There is always a lunar eclipse in between the two solar eclipses in the duo. The lunar eclipse of July 27 is total, and is in fact the longest total lunar eclipse of the 21st century, 1 hour and 43 minutes in length. As mentioned above, this total lunar eclipse occurs at the same time as the opposition of Mars, so there will be two red celestial bodies sharing the sky for 1-3/4 hours! But as you can see
from the map above, this eclipse is centered on a longitude extending from Iran to Russia, and will not be at visible from anywhere in North America.
For more information about the 2018 eclipses, and for eclipses in general, visit the 2018 page at Eclipsewise, the official website of Fred Espenak, "Mr. Eclipse." While you're there, check out all of Fred's wonderful eclipse canons, which include beautiful graphs and images along with detailed information of all the eclipses you
would ever care to know about... past, present and future. Fred's books are excellent preparation for the current Golden Age of American Eclipses.
The reason for the three-eclipse duo season is simple. There are "eclipse zones" in the Moon's orbit, one for solar eclipses and one for lunar eclipses. Whenever the Moon is in either of these zones, an eclipse occurs. In the case of a solar eclipse duo, the first eclipse occurs on the extreme western end of the solar zone. The next solar eclipse occurs at the extreme eastern end of the zone. Since these
eclipses are at opposite ends of the zone, they are very "skimpy" and shallow. But because of the motion of the Moon, the associated lunar eclipse always lands near the center of the lunar zone, which results in a very deep, long phase of totality.
There are also lunar eclipse duos, which are the reverse of solar duos. In these instances, there are two very shallow, nearly invisible penumbral lunar eclipses, separated by a month. But in between these occurs a very deep, central solar eclipse, either total or annular, which is visible over the tropics. In this way, there
is a remarkable symmetry to eclipses.
The above image is from Book 3 of ECLIPSES ILLUSTRATED, which is very nearly complete. This latest installment of this series will explain about the eclipse zones, and also duos and many other interesting aspects of solar and lunar eclipses. If you
have not yet checked out this eclipse ebook series, you might want to do so. It's very inexpensive and intended to help rookie eclipse enthusiasts learn all about eclipses, to better prepare for the current eclipse Golden Age.
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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