- Wednesday, June 11, 2003
Arcturus is actually the third brightest star in the sky, after the Dogstar Sirius, and bright Canopus, best visible south of the Equator. Since June is one of the best months to learn this star, check it out this month.
Arcturus can help us find another bright star. If you follow the arc of the Big Dipper's handle to Arcturus, you can also extend a line toward the southwest from this bright star to the bright blue-ish star "Spica" (pronounced "Spike-ah") in the constellation "Virgo" the virgin.
Spica is seen to the southeast of Leo in the sky. This is the lower left of the Lion as seen north of the Equator, but the upper right as seen from the Southern Hemisphere. Spica in only the 15th brightest star seen from Earth, but it is the next brightest star high in the evening sky of June.
There is a rule for finding these bright stars of early summer: Follow the 'arc' to Arcturus, and follow the 'spike' to Spica. It's not really hard to learn these stars since they are the brightest stars high in the sky in this season. They are also some of the few stars that can be easily seen in urban areas with a lot of streetlights. Learning these conspicuous stars will help you find your way around the other constellations.
Signs and Seasons (Gen. 1:14)
The June Solstice - The Sun at 23 1/2 Degrees North
Back in my public school days, I was taught that the Earth's axis is inclined "23 1/2 degrees" to the plane of its orbit around the sun. Like many of the things I learned in public school, this was an interesting factoid, but didn't help me very much in understanding what was going on in the sky. But this number "23 1/2 degrees" turns up in many interesting ways, especially around the solstices.
On June 21, the Earth reaches a point in its orbit where the North Pole is leaning in the general direction of the sun. As seen from the Earth's surface, the sun appears to reach the northern extreme of its annual circle through the sky. So on this day, the sun appears to "stand still" and not move further north. For this reason, the Romans called it the "solstice," which means in Latin, "The sun stands."
On the June solstice, the sun reaches its furthest extent to the north in the sky. For folks in the Northern Hemisphere, the sun is highest overhead at noon, and the noon shadows are the shortest of the year. Also, the morning sun is seen to rise furthest to north than any day of the year, and also sets furthest to the north. For this reason, the June solstice is "the longest day of the year," and "the first day of summer" for everyone in the Northern Hemisphere.
Mirror of the World
Just as the Earth has North and South Poles and an equator, the sky is also regarded as having celestial North and South Poles, and a celestial equator. And as the Earth has "latitude" to measure positions between the equator and the poles, the sky has "declination" to measure the positions in the sky between the celestial equator and the celestial poles.
The ancients realized that the sky is like a mirror of the world, since the declinations of the sky are straight overhead at the same number latitudes of the Earth. For example, if one could be at the North Pole, a latitude of 90 degrees north, one would see straight overhead the North Celestial Pole, at a declination of 90 degrees north; likewise for the South Pole and its celestial counterpart. Similarly, when at the equator (zero latitude), one would see straight overhead the Celestial Equator (zero declination).
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