- 2003 11 Jun
As we've seen in recent updates, the constellation Leo the Lion is still quite high in the skies in the early evenings of June. However, due to the Earth's constant motion, the sun continues to advance through the zodiac constellations. In early June, the sun is passing in front of the stars of Taurus the Bull. As a result, Leo is further to the west than last month, and a new set of stars is currently at their highest in the early evenings.
The Big Dipper
The Big Dipper is still high in the northern sky. If you look to the north, the Big Dipper is now somewhat to the left of the North Star after nightfall in the early evenings of June. For folks in Europe, Canada and the northern United States, the Big Dipper should be very high overhead about an hour after sunset. For folks in the southern United States, such as Florida and southern Texas, the Big Dipper ought to be quite high to the north, more than halfway from the horizon to the zenith, the point directly overhead.
The Big Dipper is probably the most famous constellation in the sky, at least for Northern Hemisphere observers. This star pattern is made up of seven fairly bright stars, four of which make up the "bowl" and three of which make up the "handle." We can use the Big Dipper to help us find the other constellations of the Spring Sky.
As we saw last month, the constellation Leo is found at a good distance "underneath" the bowl of the Big Dipper, that is, to the south. And the two outer stars of the "bowl" of the Big Dipper point toward the North Star, which is always in the same place above the northern horizon. We can find Leo in the other direction from the North Star, at a good distance "underneath" the bowl of the Dipper, that is, to the south.
The Big Dipper can help locate other stars. If you follow the curve of the handle of the Big Dipper, it leads in the general direction of the bright star "Arcturus" in the constellation "Bootes" the herdsman (pronounced "Bo-oo-teez"). This bright, orange-ish star is one of the brightest stars in the sky and therefore easy to spot. The star Arcturus can be seen high in the sky in the early evenings of June. Try to see if you can find this star from the handle of the Big Dipper.
The name "Arcturus" turns up twice in the book of Job in the King James Version of the Bible, for example:
"Canst thou bring forth Mazzaroth in his season? Or canst thou guide Arcturus and his sons?" - Job 38:32
However, it doesn't seem that this passage refers to the star known as Arcturus. According to my concordance, the Hebrew word translated as "Arcturus" means "group" or "crowd," and is identified with the constellation the Great Bear, also known as the Big Dipper. The New International Version renders this verse like this:
"Can you bring forth the constellations in their season or lead out the Bear with its cubs?"
In a footnote, the NIV says "the Bear" can also be read as "Leo." However, the scholars wish to read this verse, it seems that all readings of Job 38:32 make reference to the portion of the sky visible overhead in the early evenings this month.
In traditional western astronomy, the Greek word "Arktouros" means "bear watcher." The star commonly called Arcturus was mentioned by the Greek poet Aratus in his famous astronomical poem "Phenomena," written around 400 B.C.:
"Behind Helice, like to one that drives, is borne along Arctophylax whom men also call Bootes, since he seems to lay hand on the wain-like Bear. Very bright is he all: but beneath his belt wheels a star, bright beyond the others, Arcturus himself."
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).
23 1/2 Degrees
On the June solstice, the Earth's axis, which is inclined 23 1/2 degrees, is leaning toward the sun. As seen from the Earth, the sun reaches a declination of 23 1/2 degrees to the north of the Celestial Equator. On this day, the sun is seen directly overhead at noon at a latitude of 23 1/2 degrees north. This latitude is called the Tropic of Cancer. On the tropic, the shadows at noon disappear when the sun is directly overhead.
The word "tropic" comes from the Greek word "trope," which means "turning." This word turns up in one verse of the New Testament:
"Every good gift and every perfect gift is from above, and cometh down from the Father of lights, with whom is no variableness, neither shadow of turning." - James 1:17
After the solstice, the sun "turns" once again toward southern declinations. So the Tropic of Cancer is the "turning point" of the sun's northerly extent over the Northern Hemisphere.
As one moves north of the Tropic of Cancer, the sun does not reach as high at noon on the solstice. In South Florida for example, the noon sun is very high in the sky, but not precisely overhead, since there are very short shadows at noon.
Over the mid-temperate latitudes around 40 degrees latitude north, such as New York, Washington, Chicago and Cleveland, the noon sun is about 17 percent toward the south. But as one moves further north, the days are longer on the June solstice, and the sun rises and sets further to the north.
The Arctic Circle is at latitude 66 1/2 degrees north, which is 23 1/2 degrees from the North Pole. At the Arctic Circle, the daylight is so long on the June solstice that the sun does not set! The solstice day is 24 hours long. The sun rises due north at midnight, circles the sky all day, and sets again due north at the next "midnight." And since the days change slowly, there is constant daylight in the Arctic for much of the late spring and early summer.
At the North Pole, the "days" are six months long. The sun rises on the Equinox in March, and sets on the Equinox in September. The June solstice is the "noon" of this six-month polar day. On this day, the sun reaches its highest point in the polar sky, 23 1/2 degrees above the horizon.
Meanwhile, at the South Pole, the June solstice is the "midnight" of the six-month polar night, and the sun cannot be seen at all from here during June. At the Antarctic Circle, nighttime is 24 hours in length. The Antarctic sun can be seen briefly rising due north, and promptly setting from the same place. The Antarctic Circle is at latitude 66 1/2 degrees south, which is 23 1/2 degrees from the South Pole.
For folks in the Southern Hemisphere, the June solstice is the shortest day of the year. As one moves north from the Antarctic Circle, the period of daylight is longer, but it will still be shorter than 12 hours on this day.
After the June solstice, the sun will turn south again through the sky. A half-year from now, on the December solstice, the sun will reach a declination of 23 1/2 degrees south. On this day, the sun will pass directly overhead on the Tropic of Capricorn, at latitude 23 1/2 degrees south. And on this day, the Southern Hemisphere will have its longest day, while the Northern Hemisphere will have its first day of winter.
Jay Ryan is the creator of "The Classical Astronomy Update," a free e-mail newsletter for helping Christian homeschool families learn more about what's up in the starry sky. If you would like to receive the Update, please drop Jay an e-mail firstname.lastname@example.org.