If you stand on the Earth's equator, the celestial equator passes overhead. They are now called, respectively, declination and right ascension.ĭirectly out from the Earth's equator, 0° latitude, is the celestial equator, 0° declination. Imagine the lines of latitude and longitude ballooning outward from the Earth and printing themselves on the inside of the sky sphere, as shown at right. In the case of Earth, these are named latitude and longitude. Whenever you want to specify a point on the surface of a sphere, you'll probably use what geometers call spherical coordinates. The celestial sphere, with its infinitely large radius, appears to turn daily around our motionless Earth, from which we use telescopes to examine wonders painted on its inside surface. Perhaps for this reason, astronomers are quite comfortable living with both - as long as the two are kept in their proper relationship. In astronomy, appearances and reality are more different than in any other area of human experience. Never mind that we're on a moving dust mote orbiting a star in the fringe of a galaxy. At any time half of the celestial sphere is above the horizon, half below.Įven today this is how the cosmic setup actually looks. Part of the celestial sphere is always setting behind the western horizon, while part is always rising in the east. The celestial dome with its starry decorations had to be a complete celestial sphere, early skywatchers realized, because we never see a bottom rim as the dome tilts and rotates around the Earth once a day. When a telescope's right-ascension axis is lined up with the Earth's axis, as shown here, the telescope can turn on it to follow the rotating sky. On the celestial sphere, lines of right ascension and declination are similar to longitude and latitude lines on Earth. Celebration of Pentecost ends the cycle of Easter-related events in the Christian calendar.The Earth is at the center of the celestial sphere, an imaginary surface on which the planets, stars, and nebulae seem to be printed. Initially a part of Easter celebrations, this day was later separated from Easter, along with Pentecost. To Christians, the ascension signifies that Christ completed his work on Earth and allowed him to prepare a place for his followers in heaven. After asking them to stay, Christ then ascended to heaven to take his seat at the right hand of God, under the gaze of his disciples. As the Bible says, at the end of day 40, Jesus Christ and his disciples went to Mount Olivet (or the Mount of Olives), near Jerusalem. For 40 days after this, he stayed with his Apostles (the primary disciples of Christ) to instruct them on how to carry out his teachings. As a result, their celebrations occur at a later date than the Western event.Īs per the New Testament in the Bible, after Jesus Christ’s crucifixion on Good Friday, he was resurrected from the dead in three days, on the day we know as Easter Sunday. Western Churches prefer to use the Gregorian calendar for calculating this date, while many Eastern Orthodox Churches calculate this date according to the Julian calendar. The date, too, differs in different geographic locations. This event is celebrated primarily by Catholics and Anglican Christians most Protestant churches do not follow this tradition anymore. One of the earliest Christian festivals, Ascension Day marks the end of the Easter season.
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