Precession & Coordinates

Take a walk on the wild side

How do you convert celestial coordinates for equinox 1950.0 to 2000.0?

I use Burnham’s Celestial Handbook, which gives objects’ celestial coordinates for equinox 1950.0. How do I convert these to 2000.0, the current standard? First off, the difference isn’t great. Fifty years of precession change an object’s right ascension and declination by a total of 0.7° at most (if it’s near the ecliptic; less elsewhere)....

Uranus's rings feature in this 2005 shot from Hubble Space Telescope. NASA / ESA / and M. Showalter

What defines a planet’s north pole?

Uranus is often said to have a retrograde rotation with its axis tilted 98°. Why don’t we say it has a direct spin with the axis tilted 82°? Since 1982, the International Astronomical Union has defined the north pole of a planet to be the pole that lies north of the ecliptic plane (the...

When will (or did) the galactic equator cross the ecliptic very close to the latter’s northern and southern extremes?

As a teenager, when examining an equinox-1950 star atlas, I noticed that the galactic equator crossed the ecliptic very close to the latter’s northern and southern extremes (that is, the solstices at right ascension 6h and 18h). On equinox-2000 charts they are even closer. I’d love to know when the exact coincidence will (or...

sigma 3053

Where can I find double star SAO numbers for my Go To telescope?

I want to observe double stars, but my Go To telescope needs their SAO numbers. Where can I get them? SAO numbers come from the Smithsonian Astrophysical Observatory Star Catalog (1966). They aren’t normally used by double-star enthusiasts, who prefer special notations such as ADS 1630, S748, and Krueger 60.Finding equivalent catalog designations can...

On November 17, 2005, Prince Philip (right), the Duke of Edinburgh, and Roy Clare, director of the National Maritime Museum (NMM), sealed a time capsule marking the end of the fundraising drive for the Royal Observatory Greenwich. The capsule will go on display at the observatory's new planetarium, which should be finished in 2007. Its contents, which include a handheld GPS receiver donated by Clare, may seem dated indeed when it is opened in 2105.

Why doesn’t a GPS receiver read longitude 0° 00′ 00″ while standing on the prime meridian at the Greenwich Observatory?

Why didn’t my GPS receiver read longitude 0° 00' 00" when I visited Greenwich Observatory and stood on the prime meridian? The NAVSTAR satellites of the Global Positioning System can provide your location to an accuracy of 3 meters (10 feet) or better. The coordinates you get are based on a particular geodetic datum,...