Stars rise in the east of the sky but do not rise up straight, but instead diagonally. The diagonal goes from north (left) to south (right). After a few hours, these same stars will appear high in the southern sky. Astronomyonline.org says, "Objects in the night sky can also serve as size references. The Full Moon is 1/2º in diameter. The images of the north and south poles on the previous page have a pair of stars circled: two stars of Ursa Major, and two Stars of Crux. These two are also good rulers: the space between the two Ursa Major stars are 5º apart, and the space between the two Crux stars are 6º apart." Most commonly, stars can be found by using coordinates, which is what amateur astronomers do. Those two are altitude-azimuth and equatorial. More advanced and even professional astronomers use equatorial, ecliptic and sometimes galactic guides. Astronomyonline.org defines all these terms. "Altitude-azimuth is the simplest to define: this system is based on the observer. Altitude is up and down while azimuth is across the horizon. Zero and 180º is your horizon, and 90º is straight above - called Zenith. This system is difficult to use in Astronomy for two reasons: the celestial sphere does not rotate this way, and the coordinates of stars, planets, and galaxies are given based on the equatorial system." The other method used by amateurs is the Equatorial system. "The equatorial system is based on Earth's rotation (the sky does not really rotate, the Earth does). The axis of rotation for the equatorial system is the North and South Poles. Measurements are made by Right-Ascension (left and right - longitude) and Declination (up and down - latitude). The celestial equator is the imaginary plane that marks 0ºdeclination. Right-Ascension is measured in hours, minutes, and seconds with its 0 point (0h 0m 0s) to be the imaginary line connecting the North and South Celestial Poles crossing the Celestial Equator." Next, we have the Ecliptic Guides, "This coordinate system is based on the Sun. The North and South Poles are the points above and below the Sun, and the Equator is the extended plane of the Sun's equator. Zero meridian is the Vernal Equinox. The ecliptic plane is the orbit of Earth about the Sun.". As well as the Galactic Guides, "<span>The galactic coordinate system is based on the ecliptic, except the North and South Poles are the points above and below the center of our </span>galaxy<span>, the </span>Milky Way<span>. This is the axis of rotation. The equatorial plane corresponds to the disk plane of </span>our galaxy<span>. Zero meridian is the point in which the imaginary line connecting the galactic north and south poles crosses the galactic equator.". Stars can be located using many different methods, but these have proved themselves to be the most reliable.
