This misalignment causes seasons ; when the Sun appears North of the celestial equator the Earth's northern hemisphere receives more sunlight, while when the Sun appears South of the celestial equator the northern hemisphere receives less sunlight.
If we could view the Solar System from a point far above the North Pole, we'd see the Earth rotating counter-clockwise on its axis and revolving counter-clockwise about the Sun. Most of the other planets would also appear to rotate counter-clockwise.
In addition, the Moon would appear to orbit the Earth in a counter-clockwise direction, as would most other planetary satellites. Since our class meets in the evening, most of the times we will record are after noon, and the hour time is the time on your watch plus 12 hours.
Astronomers all over the world use a single time system to coordinate their observations. Universal Time is exactly 10 hours ahead of Hawaii time. To convert hour Hawaii time to UT , you add 10 hours; if the result is more than 24, subtract 24 and go to the next day.
To convert from UT to Hawaii time , you subtract 10 hours; if the result is less than 0, you add 24 and go to the previous day. Unfortunately, the Sun will have set here on Oahu before this interesting event begins! As a rule, we will use hour Hawaii time in this class, and write the time without any time zone. Astronomers represent the appearance of the entire sky as seen at some particular place and time by drawing circular all-sky charts.
Unfortunately, it's not really possible to capture the appearance of the sky on a flat piece of paper, so reading an all-sky chart and relating it to what you see in the sky is a bit tricky. For example, these charts distort the patterns of stars near the horizon, so you may find it hard to recognize constellations from an all-sky chart. The only way to correct this distortion is to break the sky up into several separate charts this is the approach used in The Sky Tonight , which we will use to find the constellations.
For some purposes, however, it's very convenient to show the entire sky in one chart, so you should learn to read an all-sky chart.
Now imagine you are lying flat on your back with your head pointing North ; then East will be on your left, South at your feet, West on your right, and the Zenith right in front of you. Mentally stretch the disk of the chart so that it forms a dome over your position. The positions of stars on this imaginary dome now correspond to their positions in the sky. Stars are shown as dots, with larger dots for brighter stars; the connecting lines show constellations.
The symbols show the positions of Jupiter and Saturn. The blue curve is the celestial equator, and the red curve is the ecliptic. Compass points are shown around the edge of the chart. The Water-Bearer. The Eagle. The Ram. The Charioteer. The Herdsman. The Giraffe. The Crab. Canes Venatici. The Hunting Dogs. Cor Caroli. Canis Major. The Great Dog. Canis Minor. The Little Dog.
The Sea Goat. King Cepheus. The Whale. Coma Berenices. Corona Borealis. The Northern Crown. The Crow. The Cup. The Swan. The Dolphin. The Dragon. The Foal. The River. The Twins. Pollux, Castor. The Watersnake. The Lizard. The Lion. Leo Minor. The Little Lion. The Hare. The Balance. The Lynx. The stars seem so fixed that ancient sky-gazers mentally connected the stars into figures constellations that we can still make out today.
But in reality, the stars are constantly moving. They are just so far away that the naked eye cannot detect their movement. But sensitive instruments can detect their movement.
Consider driving down the highway in the mountains at 60 mph. The telephone poles on the side of the road seem to whiz past you, but the distant mountains seem to hardly move at all. In fact, they are both traveling at the same speed 60 mph relative to you. The mountains just seem to move slower than the telephone poles because of a perspective effect known as parallax.
In general, the more distant an object, the less it moves in your field of view for a certain, fixed actual speed. The stars even the closest ones are vastly farther away than the mountains, so their motion in our field of view is miniscule.
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