This is the Classical Astronomy Update, an email newsletter especially
for Christian homeschool
families (though everyone is welcome!)
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As snow in summer, and as rain in harvest, so honour is not
seemly for a fool. - Proverbs 26:1
IN THIS UPDATE
The Second Day of Summer
This newsletter was supposed to go out last week, but I didn't get to it in time. We just returned from a short but pleasant trip to Southern California to visit our son Sam, who is serving in the Navy. This was our first to SoCal, though I spent a month in the Bay Area as a teenager in 1980. It was a refreshing break from the "hamster wheel" of day job employment. So I hope you don't mind the summer solstice
lesson being sent a day late, on the Second Day of Summer! Here's the view from 37,000 feet as the Sun set over eastern Iowa not far from the Mississippi:
Here's another view that was snapped afterwards, beautiful sunset colors as seen from high above the ground. (These images were snapped by our daughter Flo who had the window seat.)
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The Summer Solstice
Then, as our fourth study, let us set down astronomy... this study certainly compels the soul to look upward and leads it away from the things here to those higher things. - Plato (circa 350 B.C.)
On about June 21 each year, the Sun reaches the northernmost extent its annual cycle. This day is the summer solstice and is traditionally regarded as the official "First Day of Summer" for observers in the northern hemisphere. The Sun reaches its most northerly declination of the year, near the"feet" of the Twins in the constellation Gemini.
On the solstice, the Sun is at its highest point of the year in the noon sky for observers in the northern hemisphere, and the shadows at noon are the shortest they can be. In coming months following June, be sure to watch the noon shadows, and notice how the they get longer as the months go by. Since the Sun is close to the constellation Orion, this constellation is invisible during the early summer, and will
reappear in the morning sky above the sunrise sometime in August, depending on your location.
The Longest Day
On the summer solstice, you can see the Sun rising very far to the north and later setting very far to the north. For this reason, the summer solstice is also "The Longest Day of the Year." The Sun is above the horizon for the maximum portion of its 24 hour cycle and the length of daylight is greatest for people living north of the Equator.
Here in Cleveland, the daylight on the longest day lasts about 15 hours. Cleveland is near latitude 40 degrees North, along with many other large American cities, such as New York, Washington DC, Chicago, and San Francisco. So the length of daylight is about the same for these cities as well.
However, the length of summer daylight is even greater for places further north. At the Arctic Circle, the Sun doesn't even set on the Summer Solstice! If one were way up in Alaska or Iceland, one would see the solstice Sun rising in the north at midnight, wheeling a full circle all the way around the sky, and again touching the horizon in the north the next midnight!
(The solstices and other seasonal varations are discussed in detail inour
The Long Days of Summer
You may have noticed that during the long days of summer, the length of daylight doesn't change very much from week to week. For most latitudes, the length of daylight on the longest day of the year is only a few seconds different from the several days before and after. Also, the Sun's northern position only changes about 6% from about mid-May til the longest day, June 21.
During the spring, the Sun appears to climb north through the zodiac, as though climbing a hill. As the Sun reaches the top of its northern climb, it begins to "level out," and doesn't move much further to the north between May and July. (Something similar occurs when the Sun is in the "valley" of its southern extreme, during the short days between November and January.)
And as the Sun again heads south across the sky, after the longest day, it takes until late July for it to again reach the position of mid-May. For this reason, the days are still quite long for about a month on either side of the longest days.
Of course, under the Kopernikan model of the solar system, we understand that the Sun isn't really moving north and south through the zodiac. This illusion is the result of the Earth's motion around the Sun. The Earth's axis leans furthest toward the Sun on the longest day, but it is still closely inclined toward the Sun from May to July.
Try this project with your kids -- look in the newspaper or on the internet to find the times of sunrise and sunset throughout July. Notice that these times don't change much in the early part of the month but will change more quickly toward month's end.
During the long days, the length of daylight is different depending on where you are on the Earth. In the mid-northern latitudes where I live, near 40 degrees North, the summer Sun doesn't set til almost 9:00 PM and the twilight is still quite bright until about 10 o'clock. This can really mess up the bedtime routine with the kids! It must be even worse for kids living further north because the long days are even longer
into Canada and northern Europe. Sunsets can be as late as 11:00 PM in Scotland and Russia! And most people have heard that daylight lasts 24 hours in the Arctic!
But as you move south, the long days are not as long. In the southern USA, the summer Sun goes down by 8:00 PM, depending on location. In some latitudes of the Tropics, the Sun sets at 7:00 PM. Northern dwellers having a summer vacation in the Tropics are often surprised by this, since night falls so quickly in the warm climates. And of course, the Sun rises on the Equator at about 6:00 AM every day, and sets at 6:00 PM,
since every day on the Equator is 12 hours long.
Til next time, God bless and clear skies,
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