| Name |
Explanation |
Links (left-click on the link) |
| Celestial sphere |
the infinite imaginary sphere with the earth at its center on which the stars, planets, and other heavenly bodies appear to be located. |
 |
| Circumpolar stars |
a star that does not go below the horizon, from a given observer's latitude. North circumpolar stars are stars that never set --like the Big Dipper -- and are found above the horizon. These stars are observed within 40º latitude of the north celestial pole(+50º and +90º declination). South circumpolar stars , instead, never rise as they are found below the horizon, within 40º latitude of the south celestial pole -- for example the stars in the constellation of Crux, the Southern Cross |
Celestial Sphere |
| Ecliptic |
the apparent path that the Sun traces out along the sky, in relation to the stars, as viewd from Earth.
It is in fact the geometric plane of the Earth's orbit around the sun making an angle of about 23 degrees with the equator. All of the planets rotate the sun in approximately the same ecliptic. |
Very good graphical representation |
| Equinox |
it occurs around March 20 (vernal equinox) and September 22 (autumnal equinox) each year, when the Sun can be observed to be directly above the Earth's equator. Night and day, on these dates, are nearly of the same length and the Sun crosses the celestial equator at declination 0. |
Geocentric and heliocentric views |
| Sideral day |
is the time taken by a star (i.e. the Sun) to cross the observer's meridian two times successively.In actual fact, it is the time interval it takes for Earth to make a complete rotation using the stars as reference. A sidereal day is 23 hours, 56 minutes abd 4 seconds long. |
Sideral day |
| Solar day |
is the time taken by Earth to make a complete rotation using the Sun as reference. The solar day is longer than a sidereal day because Earth orbits around the Sun, while rotating on its axis. |
Solar day |
| Solstice |
it occurs twice a year, on June 21st (Summer solstice) and December 22nd (Winter solstice), when Earth's axis tilts the most toward or away from the Sun, causing the Sun to be farthest north or south at noon. Summer solstice is found at 23.5ºN latitude in the Tropic of Cancer, and the Winter solstice is found at 2.5ºN latitude in the Tropic of Capricorn. |
Geocentric and heliocentric views |
| Zodiac |
the belt around the sky, about 16°wide, centered on the ecliptic containing 12 constellations |
The 12 Constellations of the Zodiac |
...Back to MainPage at LillyvalleyInternational.co.uk