Sign in with your library card Please enter your library card number. Related Content Related Overviews vernal equinox. Show Summary Details Overview right ascension. Reference entries right ascension in A Dictionary of Astronomy 2 rev Length: 88 words. All rights reserved. Sign in to annotate. Delete Cancel Save. It also does not make sense to say, for example, that the Right Ascension of Raleigh is now 21 h 00 m.
Places do not have a Right Ascension. Look at the diagram below. Let's say that star 2 has a Right Ascension of 06h 00m. The entire celestial sphere slowly moves from left to right over the course of the night, so the positions in relation to the horizon and the meridian of all the stars shown slowly change. In the diagram, star 2 is just now transiting our local meridian, so our local sidereal time is 06h 00m.
Star 1 has a right ascension of 05 h 00 m. Star 1 already transited 1 hour ago. When star 1 was on our meridian, our sidereal time then was 05h 00m.
Star 3 has a right ascension of 07 h 00 m. When star 3 transits our local sidereal time will be 07 h 00 m. Since our local sidereal time is now 06 h 00 m , star 3 will transit in one hour. Since you know Vega's R. There's no particularly bright star at this "0" point, however, the two stars along the eastern side of the Great Square of Pegasus make good substitutes. They're close enough to 0h R. From there east, R. The best reference for R. Luckily, they come cheap on the Internet.
Remember that the time on the clock the R. By: Bob King November 10, By: Camille M. Carlisle November 9, Community Leaders: Notable Astronomers. By: Richard S. Wright Jr. November 9, By: Jennifer Willis November 8, Astronomy in Space with David Dickinson.
By: David Dickinson November 4, By: Bob King October 27, By: David Dickinson October 20, Celestial Objects to Observe. October 19, Solar System. By: Bob King October 18, Constant Contact Use. Emails are serviced by Constant Contact. The sky is draped in an invisible coordinate grid that will help you easily find any object you wish, the same as you would locate a city on a map.
You'll occasionally see the East and West longitude suffixes replaced by a negative sign for the western hemisphere and a positive sign for the eastern hemisphere. CC0 1. Every city on the planet has a unique latitude and longitude, its "spot" on the grid. Detroit, Michigan, is shown here. Here's Earth inside the big soccer ball. Declination green is measured in degrees north and south of the celestial equator. Right ascension, akin to longitude, is measured east from the equinox.
The red circle is the Sun's apparent path around the sky, which defines the ecliptic. Here's a slice of sky bisected by the celestial equator with hours of right ascension RA labeled along the top and declination Dec. The coordinates of the bright stars Betelgeuse and Sirius are also shown. This view shows the north celestial pole NCP and polar regions. By convention, 0 h is used instead of 24 h. Tags celestial sphere. Stew Shouldice Log in to Reply You must be logged in to post a comment.
Log in to Reply You must be logged in to post a comment. Anthony Barreiro February 26, at pm Bob, this explanation would fit nicely in the first chapter of your next book! Here are the bright circumpolar stars that happen to lie close to an exact hour of right ascension: Beta Cassiopeiae 0 h Gamma Cas 1 h Epsilon Cas 2 h Alpha and Beta Ursa Majoris Dubhe and Merak, the pointer stars 11 h Gamma UMa 12 h Epsilon UMa 13 h Beta Ursa Minoris Kochab, the brightest star in the bowl of the little dipper 15 h Gamma Draconis Eltanin, the brightest star in the head of the dragon 18 h Put Polaris at the middle of your imaginary clock face, find whichever of these stars are visible, and interpolate the rest of the clock.
Anyway, it's a bit of fun that needs neither optical aid nor an especially dark sky. It's easy to go down a rabbit hole with timekeeping. But it's fun. Ugochuks September 20, at am Please sir can you explain to me how I can convert RA in degree minute second to arcsecond Log in to Reply You must be logged in to post a comment.
Here's question 1: 1 If the Right Ascension is referenced from "Vernal Equinox" position "0hr", in the year , then why does nobody ever talk about the physical location? Ugochuks March 1, at am Thank you so much for your help sir Log in to Reply You must be logged in to post a comment.
Luvlivemusic March 11, at pm Hey Bob! Spherical trigonometry is handy for converting between coordinates systems. Positions of stars and other objects in the sky can be used for navigation now laregely made obsolete by Global Positioning Systems.
For example, the elevation of the North Star above an observer's horizon is equal to the observer's latitude:. The Earth's rotation is used a basic unit of time measure -- the day. If you keep track of the intervals between successive times of maximum elevation of the Sun above the horizon e.
These differences result from two causes -- first, we measure time with respect to the Earth's rotation axis and hence equator while the Sun's motion is along the ecliptic, and second, the Earth's orbit is elliptical and the Earth moves faster along its orbit when closer to the Sun. We also use the time that it takes the Earth to orbit the Sun as a time unit, the year.
Note that several different lengths of a year can be defined depending on what reference is used:. Seasons on our Home Planet. Seasons result from the The seasons are obviously opposite in the Earth's two hemispheres. The polar direction is slowly changing due to precession direction takes 26, yrs to complete one circuit but the angle between the polar axis and the ecliptic is fixed and invariant. We also tend to identify various constellations with the seasons because the stars visible at night change throughout the year.
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