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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.
IN THIS UPDATE:
- Anouncements
- Look for Signs & Seasons at Your Homeschool Convention
- Dance of the Planets
- Astronomy Topics
- Using the Signs & Seasons Volvelle
- Question About Polaris
Thus saith the LORD, which giveth the sun for a light by day, and the
ordinances of the moon and of the stars for a light by night, which
divideth the sea when the waves thereof roar; The LORD of hosts is
his name: If those ordinances depart from before me, saith the
LORD, then the seed of Israel also shall cease from being
a nation before me for ever. - Jeremiah 31:35-36
Welcome to the Classical Astronomy Update!
Hello Friends,
It's been very busy around here since the last newsletter in early March. Classical Astronomy attended two homeschool conventions, APACHE in Peoria, Illinois and the Midwest Homeschool Convention in Cincinnati, Ohio. Many subscribers of the Classical Astronomy Update came to our table to mention that they enjoy and benefit from reading this newsletter. Many thanks to everyone who dropped by. And welcome to all the new subscribers that have joined since those conventions. Hope you learn many new things about the sky.
One question I was asked by several convention attendees is "why should we be interested in bothering with astronomy?" This is a very common question, as our modern culture regards astronomy as a very dispensible elective subject. However, in pre-industrial culture, astronomy was essential for many aspects of daily life, such as understanding the cycle of the growing season. The growing cycle for food and other plants remains one very basic way that astronomy impacts the life of every person.
We saw the growing cycle illustrated as we were driving to Cincinnati. When we left Cleveland, way up on the northern border of the USA, the trees were only just beginning to put out buds. As we drove the 250 miles to Cincinnati, it was easy to notice that the plants were becoming more green as we moved south. It was like a time-lapse movie where the trees seemed to grow as we headed down the road. By the time we arrived in Cincinnati, after only about four hours, the trees were in full bloom. Our family saw the same thing in 2003 in early April while beginning our big Florida Vacation. Check out this Update article, Spring Blooms From North to South
.
This is an illustration of moving through climate zones at the beginning of the growing season. We can see the same cycle again in the fall at the time of peak colors. Trees in the northern zones will reach peak colors while trees in the southern zones are still green. The division of climate zones is only one aspect of how Classical Astronomy is highly relevant to our daily lives.
* * * * *
Please keep in mind that, in June, my whole family will be joining me for the SEARCH homeschool conference in Souderton, Pennsylvania, the weekend of June 18-19, 2010. The next weekend, we'll also be down the road in Akron, Ohio for the CHEO homeschool convention, June 24-26, 2010.
For a summary of the talks that I'm giving these days, please check out my speaker profile at the TOS Homeschool Speakers Bureau:
Announcements
Look for Signs & Seasons at Your Homeschool Convention
When we were at the conventions in the past month, a number of people came to the booth to look over our Signs & Seasons homeschool astronomy curriculum. Many of these browsers remarked that they had seen the book reviewed and advertized but they wanted a chance to actually look it over before they considered buying it.
So far, we've been unable to attend very many conventions. Though many convention vendors carry Signs & Seasons in their catalogs and online stores, not many have brought the curriculum to conventions. However, we're happy to report that two convention vendors are bringing Signs & Seasons for 2010! Please visit these vendors at the following conventions this year. And if you do decide to purchase Signs & Seasons
, please be sure to mention you heard about their booth in the Classical Astronomy Update!
Dance of the Planets
The Spring Planets
As we've been mentioning in the Classical Astronomy Update, the bright planet Mars has been a regular feature in the evening sky since January. Mars completed its retrogradation in March, and since then has been moving east through the constellations of the evening sky. Mars has been moving away from the stars Castor and Pollux in the constellation Gemini, and is currently heading toward the constellation Leo. Keep your eye on Mars high overhead on spring evenings this year as it will pass near Regulus, the brightest star in Leo, on June 6, a conjunction of these two celestial bodies.
Also in the evening sky this spring is the planet Saturn, currently passing out of the constellation Leo. The star Regulus just so happens to lie near the ecliptic, which is a circle in the sky representing the plane of the Earth's orbit, and generally coresponds to the the plane of the solar system. So when you're gazing up at Leo in the evenings this spring, and when you see the planets Mars and Saturn lined up with Regulus, you're actually looking up from the Earth and out along the plane of the solar system.
The waxing Moon will pass Mars, Regulus and Saturn over a span of evenings over the next several days. Look for the Moon to make its closest pass of Mars on the evening of Wednesday, April 21. The Moon will be east of Mars the next night, and will pass on either side of the star Regulus on the evenings of April 22 and 23, as seen from North and South America. The Moon will pass on either side of Saturn on the evenings of April 24 and 25. The closest passage between the Moon and Regulus and Saturn will favor the Middle East and central Asia, if you happen to live in those areas.
As mentioned in the previous Update, keep your eyes on Mars and Saturn, along with the bright Evening Star Venus throughout the coming months, as these planets will draw closely together during August, 2010. Mars will pass nearest to Saturn on the evening of August 1. Venus will be nearby on this evening, and will draw nearer over the following nights. Venus will make its closest approach to Saturn on the evening of August 9, and will be closest to Mars on the evening of August 13. If all that celestial excitement is not enough, the crescent Moon will join these planets on the same evening, August 13, 2010!
(The motions of the Moon and planets are explained in detail in our Signs & Seasons astronomy curriculum. Please check it out if you'd like to learn more! )
Astronomy Topics
Using the Signs & Seasons Volvelle
We recently received a question from a reader named Sherri concerning the operation the Orion-Constellation volvelle in Chapter 5 of the Signs & Seasons workbook. As described in the Signs & Seasons
course, volvelles are traditional dial tools that have been used for centuries to simulate the motions of the Sun, Moon and stars. The workbook includes copyable templates for cutting and assembling three different volvelles, to help the student get a "hands on" understanding of the motion of the celestial bodies.
Sherri asked how to use the volvelle to find the sunrise, sunset, and meridian times of the Sun for a particular date. Sherri was not sure where to point the Sun onto a given zodiac constellation for a particular date, for example, January 21.
I scanned my own volvelle to show the Sun wheel aligned with the date for January 21, which automatically aligned the Sun with the position along the constellations. The Sun was aligned at Noon for convenience, which is generally the meridian time, not corrected for standard time.
To find the sunrise, the Sun wheel and constellation wheel are both moved to the eastern horizon, as shown in the next scan. As we can see, at this position, the Sun is very far to the south of due east, as it actually is during the winter. Once the Sun is aligned with the horizon, you can use the Sun as an "hour hand" to read the time of sunrise indicated along the circumference of the vovelle. The volvelle indicates 7:00 AM.
To find the time of sunset, you simply turn the Sun wheel and constellation wheel to the western horizon, and read off the indicated time, again using the Sun as an "hour hand" to point at the time with which it is aligned, which is about 5:00 PM. As the volvelle depicts, the Sun sets south of due west during the winter months.
The whole idea of the volvelle is to simulate the motions of the Sun, Moon and stars. It's not a perfect simulation for many reasons, but is intended to give a ballpark idea of how these motions transpire. The volvelle must be corrected for the user's position in the standard time zone, and for daylight savings. There is also considerable variation for latitude, as a very different reading will be obtained in Alaska than in Florida. Additionally, a volvelle is a flat disc with regular rotations, and cannot perfectly simulate the irregular motions of the celestial bodies, as they appear in a spherical sky. If you compare the volvelle sunrise times to the times you'll find on the US Naval Observatory website, the numbers will probably be off by as much as 15 or 20 minutes.
Volvelles are just a crude (but traditional) simulation, intended to illustrate the general idea of these celestial motions. But if we can learn how to use them, they can help us get a better understanding of how the Sun, Moon and constellations move across the sky over the span of days, months and years.
Question About Polaris
We recently received an email asking a question about a depiction of the North Star, Polaris, from our Signs & Seasons homeschool astronomy curriculum....
Hi Mr. Ryan,
I am 11 years old. I am on chapter 4 of your Signs and Seasons curriculum. Is it ok to ask you questions if I am confused about something I am reading in the book (if my parents can't answer the question)?
If so, my question is on page 80. The text says that the earth's axis is continually pointed at Polaris. If so, how can the earth's axis remain pointed at Polaris even when it is at different positions in its orbit around the sun? See the pictures on page 80. In both pictures of the celestial sphere, it shows the earth's axis pointing TOWARD Polaris but not directly at it.
Thank you for your time.
Janson
Hi Janson, thanks for writing, I'm happy to answer your question, and it is a very good question. I've done my best to show things with the illustrations, but what I could not show on p. 80 is that the celestial sphere is REALLY BIG, almost infinite in size compared to the orbit of the Earth around the Sun. Remember how this was explained on p. 39.
Anyway, in reality, the nearest stars are about 6000 times the distance of the Earth to the Sun, and most stars are many times farther than that. There's really no way to actually show that in a book, since the scales of the sizes are so big, they couldn't be properly shown on a page. So on p. 80, you'd have to imagine the celestial sphere as much bigger and the orbit of Earth as much smaller. It would be as though the two arrows pointing at Polaris from either side of the Earth's orbit were so close together that you couldn't tell them apart. You might want to try redrawing the pictures on p. 80 on your own with a very large celestial sphere and a very tiny Earth orbit, just to make the idea more clear. Use a whole piece of paper, or even a really big sheet. Maybe you could use sidewalk chalk to make the biggest sphere possible with the tiniest Earth orbit in the middle.
 (This picture gets across the idea a little better, but you'd still need a much bigger sphere!)
The idea you've figured out on your own is stellar parallax. The general idea is, when looking at something off in the distance, you can see a shift from two closer positions. For example, look at a tree or other object off in the distance. Now hold your thumb at arm's length. Close one eye and look at your thumb, noticing the position of the distant object. Now close your other eye and notice the position of the distant object. The shift in position is the parallax difference between your two eyes. Astronomers use a similar technique to measure tiny parallax differences in stars as seen from one side of Earth's orbit and the other. In this way, astronomers can use geometry to measure the positions of the closest stars, and this technique is considered accurate for measuring stars up to about 100 light years from the Earth.
There is a tiny wobble in the position of Polaris due to the Earth's orbit, but it's much too small to see with the eye. In fact, the amount of parallax wobble measured by astronomers for Polaris is about 8 milliarcseconds, or about two-millionths of a degree! You might want to google "stellar parallax" to learn more about the concept.
Coming in future Classical Astronomy Updates:
- We'll continue to follow the monthly motions and lunar conjunctions of Venus, Mars and Saturn throughout 2010.
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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