Bob Doyle, Columnist
How can one tell one star from another at night? It’s a matter of knowing the sky areas (constellations).
Constellations are analogous to countries in the sky. Every part of the sky belongs to one of 88 constellations. But unlike countries on the globe, the constellations have depth. In the same constellation, some stars are close while others may be much farther away.
Star distances are expressed in light years, the distance that light travels a year. Since the nearer bright stars are dozens of light years away, their light is dozens of years old, the time it takes light to travels from them to us.
The star Deneb, now seen in the northeastern sky in mid evening is 1,500 light years away; just think what major events have taken place in human history as this star’s light flew to Earth.
The constellations visible each evening change from season to season as we travel about the sun. The sky areas best seen are those in the opposite direction to the sun.
This is analogous to driving around the Baltimore Beltway. When we are in the north part of the beltway, to the north is Towson. If we are on the east side of the Beltway, to the east is Annapolis.
Each season has different bright star patterns seen in the evening sky. In winter, the best star pattern is Orion, the Hunter with his three star belt. Spring’s best star pattern is the Big Dipper, upside down and above the North Star. On summer evenings, the Scorpion resembles a letter “J” low in the south.
If we were to watch the stars for several hours, we would notice how the stars slowly creep across the sky. In the north, the stars seen are moving circularly about a point about halfway up.
Here is the North Star, the star about which the heavens seem to revolve. This is an illusion; it’s the Earth’s rotating motion that makes the stars appear to creep. The North Star is nearly in the same direction as the axis of the Earth.
In the east, the stars rise and move to the right. In the south, the stars move horizontally to the right. In the west, the stars drop lower and move to the right.
How does one find the planets? We must realize that even the nearer planets at their closest appear as points of light. The two brightest planets are Venus and Jupiter and outshine any night stars.
The planet’s light comes from the planet’s disk and some of its light comes into our eyes. The stars are very far away and their light is a slender thread, easily disturbed by heat waves in out atmosphere. This causes the star’s light to flicker off and on (twinkling).
Currently the two brightest planets are at a low angle to the sun and tough to spot. Low in the western dusk is the planet Jupiter. Just as low in the southeastern dawn is the planet Venus.
In the southwestern evening sky are the planets Mars and Saturn. Mars lies to the right of the bright star Spica. Saturn is the right of the Scorpion (a starry “J”).
SKY SIGHTS AHEAD: On June 12, the moon was full and opposite the sun. As the moon moves along its orbit, it is rising later each night. In a few days, the moon will be rising after midnight.
If clear, the Milky Way may be visible from rural locations. The Milky Way is a ghostly glow that extends across the eastern sky and is brightest in the south. On June 21, summer officially begins as the sun appears farthest north and we have our longest daylight (15 hours).
Bob Doyle invites any readers comments and questions. E-mail him at email@example.com . He is available as a speaker on his column topics.