Celestial Sphere:What we see, it contains the stars, planets, Sun, and Moon Celestial Equator- the imaginary line that divides the planet into Northern and Southern hemispheres. The celestial equator is a similar imaginary circle around the celestial sphere, also known as the visible universe. The celestial equator divides the visible universe in two, creating the Northern and Southern celestial hemispheres. This helps us locate celestial bodies. Ecliptics -an imaginary line on the sky that marks the annual path of the sun. It is the projection of Earth’s orbit onto the celestial sphere.
Besides define the path of the sun, the ecliptic marks the line along which eclipses occur, the moon and planets and asteroids wander, the Zodiac constellations live. The ecliptic is even the starting point for the celestial coordinate system used by astronomers to pinpoint the location of every star, nebula, and galaxy. Meridian-a great circle of the earth passing through the poles and any given point on the earth’s surface. The half of such a circle included between the poles. Astronomy. the great circle of the celestial sphere that passes through its poles and the observer’s zenith. A point or period of highest development,greatest prosperity,or the like. an of the path way sin the body along vital energy flows. Zenith-The point on the celestial sphere that is directly above the observer.
The upper region of the sky.The highest point above the observer’s horizon attained by a celestial body. Nadir-the point of the celestial spherethat is directly opposite the zenithand vertically downward from the observer Celestial Poles-Either of two diametrically opposite points at which the extensions of the earth’s axis intersect the celestial sphere. Either of the two points at which a northward or southward projection of the Earth’s axis intersects the celestial sphere. The north and south celestial poles are analogous to Earth’s geographic poles and are used in determining right ascension in the equatorial coordinate system. Depending on which hemisphere an observer is in, the stars and other celestial objects appear to revolve once around the north or south celestial pole every 24 hours, an effect produced by the rotation of the Earth on its axis.
Because of the precession of Earth’s axis, the celestial poles gradually shift position in the sky over a nearly 26,000-year cycle. Solstices-As the Earth travels around the Sun in its orbit, the north-south position (declination) of the Sun changes over the course of the year due to the changing orientation of the Earth’s tilted rotation axes with respect to the Sun. It is this change in the position of the sun that is responsible for seasons.
Solstices occur when Sun reaches maximum offsets from the equator projected on the sky . This offset corresponds to thetilt angle of Earth’s rotational axis with respect to its orbital plane, called the Earth’s obliquity.either of the two times a year when the sun is at its greatest distance from the celestial equator: about June 21, when the sun reaches its northernmost point on the celestial sphere, or about Dec. 22, when it reaches its southernmost point. Either of the two points in the ecliptic farthest from the equator.
•Equinoxes-Either of the two points on the celestial sphere where the ecliptic(the apparent path of the Sun) crosses the celestial equator. The point at which the Sun’s path crosses the celestial equator moving from south to north is called the vernal equinox. The vernal equinox marks the zero point in both the equatorial and ecliptic coordinate systems; horizontal angular distances are measured eastward from this point.
The vernal equinox is also known as the first point of Aries because when first devised some 2,000 years ago this point occurred at the beginning of Aries in the zodiac. The point at which the Sun’s path crosses the celestial equator moving from north to south is called the autumnal equinox. •Longitude-Lines of longitude, called meridians, run perpendicular to lines of latitude, and all pass through both poles. Each longitude line is part of a great circle. There is no obvious 0-degree point for longitude, as there is for latitude. Throughout history many different starting points have been used to measure longitude. By international agreement, the meridian line through Greenwich, England, is currently given the value of 0 degrees of longitude; this meridian is referred to as the Prime Meridian.
Longitude values are indicate the angular distance between the Prime Meridian and points east or west of it on the surface of the Earth. •Latitude-A line connecting all the points with the same latitude value is called a line of latitude. This term is usually used to refer to the lines that represent values in whole degrees. All lines of latitude are parallel to the Equator, and they are sometimes also referred to as parallels. Parallels are equally spaced. There are 90 degrees of latitude going north from the Equator, and the North Pole is at 90 degrees N. There are 90 degrees to the south of the Equator, and the South Pole is at 90 degrees S. When the directional designators are omitted, northern latitudes are given positive values and southern latitudes are given negative values.
•Right Ascension-The azimuthal angle at which the hour circleof a celestial object is located. The rotation axis taken as the direction of the celestial pole. Right ascension is usually measured in units of time (hours, minutes, and seconds), with one hour of time approximately equal to 15° of arc (360°/24 hours=15°/hour). •Declination-On the celestial sphere, the position of a celestial object north or south of the celestial equator. Declination is measured in degrees along a great circle drawn through the object being measured and the north and south celestial poles, with positive values north of the celestial equator and negative values south of it, so that the equator itself is 0° and the north and south celestial poles are +90° and -90° declination respectively the angular distance of a celestial body north or to the south of the celestial equator; expressed in degrees; used with right ascension to specify positions on the celestial sphere
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