Basic motions of the sky. There is a clock calendar in the sky, the diurnal motion and the annual motion, the diurnal is the daily motion, brings the sun from the east to west and the stars rising in the east and setting in the west. Motion of the sky is obvious. There are two poles, object close to poles are circumpolar, meaning that they do not pass below or rise up from the horizon. All other stars are equatorial, meaning that they rise and set.
The pole of the sky is at zenith, at North Pole all stars are circumpolar. At equator all stars rise and set, all stars are equatorial. At intermediate latitudes there are both circumpolar and equatorial stars. Stars at highest point cross celestial meridian, which passes through observer' s longitude. That includes the sun, when it crosses the celestial meridian, defined as astronomical noon, when sun is at highest point.
The sun is never directly overhead at our latitude....Astronomical midnight is when sun crosses the celestial meridian below your feet.. Rates of object in sky. 360 degrees in 24 hours, 15 degrees per hour, one finger's width at arm's length..
Annual motion of the sky, brings in new constellations as the year progresses.
Ancient view is that sky moves around earth. Earth moves about 1 degree per day, toward east, so constellations move about 1 degree per day toward the west. Four minutes per day, bring constellation overhead back to same position one year later..
Sun moves in path called ecliptic.. Moves against twelve constellations along ecliptic called constellations of the zodiac, or signs of the zodiac. Ancient priests called zodiac constellations sun occupied on day of your birth your sun sign. Basis of natal horoscope. Diurnal and annual motion compete against each other-- Diurnal motion carries sky east to west during the day and the annual motion carries the sun eastward in the sky over the course of an entire year.
Daily motion due to rotation of the earth, width of time zones about 15 minutes about 15 minute per hour, or 360 degrees in 24 hours. Group called circumpolar and equatorial changes as we move north or south. At north pole all stars below horizon stay below horizon, all stars above horizon stay above.
At equator all stars rise and set. Best place for observatory is equator, but there are not many places at equator where observatory could be placed. Highest point above observer called zenith. Objects crossing observer's celestial meridian said to be in transit... Sun moves like a star.. when sun crosses celestial meridian called noontime. Sun is not directly overhead but is at its highest point for the day. Lowest point called celestial midnight. Astronomer priests would watch the sunrise and mark position of sunrise, throughout the year. Could determine time of year, first calendar.
At summer solstice sun rises at most northerly position, highest point reached in the sky for the year, is longest day, moves a little more to the south every day, until 3rd week in September, vernal equinox, equal day and night. in December well to the south, tracking low in the sky, sun not as warm, sun is up least time, now starts to move north, called winter solstice, early priests worried that sun might fall off the horizon, were relieved to see that it started back north. Romans celebrated the winter solstice, called Saturnalia. Egyptians gave Romans the calendar.. 12 months each 30 days....
Early Christians decided that Saturnalia would be good time to celebrate Christ's birthday. Called horizon calendar. Monuments such as Stonehenge, stone markers for sun and moon and bright planets. From our standpoint looks like the sun is set against constellations that we cannot see. During the course of one year, sun moves against the 12 constellations of the zodiac. Can call the sky the celestial sphere, with celestial equator coinciding with earth's equator.
Angle between celestial sphere and north pole is 23.5 degrees. Inclination of earth with ecliptic cause of seasons. When north pole faces the sun we are in summer, when north pole is in darkness we are in winter. Stars fall into fixed stars, constellations are fixed... Since stars are fixed, we can say that they are far away..
Wandering stars called planets... Wander through constellations, meteors are not stars, sometimes called shooting stars....comets are not stars.. Direct line to astronomy comes through Babylonians.. Babylonians gave us star charts.. Patterns do not change. Astronomers limited because they were fatalistic. Believed that things happened because the gods willed them. Babylonians did not construct models.. Believed that time was endless.