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Right ascension definition astronomy how to#
Right ascension definition astronomy manual#
Right ascension definition astronomy full#

Right ascension definition astronomy full#

Ideally the GHA of aries should not vary relative to the stars, unfortunately, as Hipparchus noted a long time ago, the earth wobbles, its axis doing a full circle in about 26000 years (if my memory is correct) which means that the first point of Aries slowly drifts across the background of stars, making a full circle in 26000 years. So to calculate the GHA of a star all you have to do is: GHA(star) = SHA(star) + GHA(aries). The SHA of the stars is simply a coordinate relative to this point. Because the fixed stars (they are not really fixed, but they are so far away that they don't seem to move much), don't move relative to each other, rather than give the GHA of each star for each hour of the day, for each day of the year, the Nautical Almanac publishes only the list of GHA for a fictitious point called "first point of Aries" (also denoted by the Zodiac sign of the Ram). LHA : LHA (Local Hour Angle) is the angle between the meridian of the celestial object and the meridian of the observer, LHA = GHA(of celestial object) - Longitude (of observer). GHA : GHA (Greenwich Hour Angle) indicates the position past the plane of the Greenwich meridian measured in degrees. it is followed by North or South same as latitude. It might help you gain a better understanding.ĭeclination : This marks the height above or below the equatorial plane for celestial objects.

Right ascension definition astronomy how to#

He has some very good chapters on astro navigation and how to apply the various calculations. This link ( ) will take you to an on line book called "The American Practical Navigator", commonly called "Bowditch". It's likely not relevant to the discussion questions, but the definitions may aid in understanding.įor Chris - You said you were trying to understand the calculations and how they apply. Everything is based on Aries and calculations go from there. They're generally the same as or show the relationship to astronomy terminology. Moving to any any astro expertise I may have, I've copied a couple of astro-navigation terms below.

I find visually identifying the celestial equator can give a good understanding of how the stars are moving around my location and can assist with "roughly" adding or subtracting for RA to point in the general direction needed. Conversion doesn't help much with an alt azimuth mount (ie a dob, like I use).

Right ascension definition astronomy manual#

Manual Equatorial mounts need this RA information more as you move around the celestial coordinate system. It is alternatively defined as the ascension (point on the celestial equator which rises with a specified celestial object) as seen from any point on the Earth's equator, where the celestial equator intersects the horizon at a right angle.I think the GOTO systems take all of this into account for us. H = LST − α, where LST is the local sidereal time.Īlong with declination, right ascension determines the direction of a point on the celestial sphere in the equatorial coordinate system. The hour-angle, H, and the right ascension, α, are related by the simple formula

1988, Peter Duffett-Smith, Practical Astronomy with Your Calculator, page 35,.

in cases where great accuracy is required, as is now done in the Nautical Almanac for 24 of the brightest stars for 10 days in the year, and those numbers in the Nautical Almanac are to be preferred. The right ascensions and declinations obtained by the preceding calculations, are the mean values, to which must be applied the corrections for the Nutation and Aberration Tables XLII.

1826, Nathaniel Bowditch, Jonathan Ingersoll Bowditch, American Practical Navigator, US Hydrographic Office, page 280,.

The sun's right ascension in time is useful to the practical astronomer in regular observatories, who adjusts his clock by sideral time.

1819, William Nicholson, Ascension, entry in American Edition of the British Encyclopedia, Volume 2, unnumbered page,.

( astronomy ) The angular distance east of the vernal point (the solar zenith at the march equinox) the celestial equivalent of longitude.

Right ascension ‎ ( plural right ascensions ) Diagram of a star's right ascension and declination as seen from outside the celestial sphere Noun