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Right ascension and declination as seen on the inside of the celestial sphere. The primary direction of the system is the March equinox, the ascending node of the ecliptic (red) on the celestial equator (blue). Right ascension is measured eastward up to 24 h along the celestial equator from the primary direction.
Many Right Ascension setting circles therefore carry two sets of numbers, one showing the value if the telescope is aligned in the northern hemisphere, the other for the southern. Even with some inaccuracies in polar alignment or the perpendicularity of the mount, setting circles can be used to roughly get to a desired object's coordinates ...
For example, the proper motion results in right ascension in the Hipparcos Catalogue (HIP) have already been converted. [12] Hence, the individual proper motions in right ascension and declination are made equivalent for straightforward calculations of various other stellar motions. The position angle θ is related to these components by: [2] [13]
Sirius can be observed in daylight with the naked eye under the right conditions. Ideally, the sky should be very clear, with the observer at a high altitude, the star passing overhead, and the Sun low on the horizon. These observing conditions are more easily met in the Southern Hemisphere, owing to the southerly declination of Sirius. [77]
Declination (vertical arcs, degrees) and hour angle (horizontal arcs, hours) is shown. For hour angle, right ascension (horizontal arcs, degrees) can be used as an alternative. The equatorial coordinate system is a celestial coordinate system widely used to specify the positions of celestial objects.
The other two cover the equatorial region of the celestial sphere, from the declination of 30° south to 30° north. The two equatorial charts are mercator projections, one for the eastern hemisphere of the celestial sphere and one for the western hemisphere. Note that unlike familiar maps, east is shown to the left and west is shown to the right.
The location is defined by a pair of angular coordinates relative to the celestial equator: right ascension (α) and declination (δ). This pair based the equatorial coordinate system. While δ is given in degrees (from +90° at the north celestial pole to −90° at the south), α is usually given in hour angles (0 to 24 h).
Right ascension and declination as seen on the inside of the celestial sphere. The primary direction of the system is the vernal equinox, the ascending node of the ecliptic (red) on the celestial equator (blue). Declination is measured northward or southward from the celestial equator, along the hour circle passing through the point in question.