Interactive Astronomy Pages

The Eternal Dance of the Sun and Moon

• What date is Easter this year?
• What are the phases of the Moon this month?
• What's a Blue Moon? And is there one this year?
• How many eclipses are there this year?

• Sun-Moon hour angle data for use with Heiner Thiessen's British Sundial Society article.

Don't know your latitude and longitude?

• In the United States, use the Geographical Name Server at the U.S. Bureau of the Census.
• In England, Wales and Scotland, convert Ordnance Survey grid coordinates to latitude and longitude.
• In Northern Ireland, convert Irish Grid coordinates to latitude and longitude.

• A set of Java applets to convert between OSGB, OSNI and latitude/longitude.
  • OSGB (British National Grid) to latitude/longitude
  • Latitude/longitude to OSGB (British National Grid)
  • OSNI (Irish Grid) to latitude/longitude
  • OSNI (Irish Grid) to OSGB (British National Grid)

When you do know your latitude and longitude ...

• Calculate the distance between any two points on the Earth, using a formula that takes into account that the Earth isn't a perfect sphere.

Reviews and acclaim for these pages

• These pages were reviewed in the January 1997 issue of Sky & Telescope magazine.
• Once in a Blue Moon was featured as The Learning Kingdom's Cool Site of the Day for 2 April 1998.
• Librarians' Sites du Jour featured these pages in their April 1998 selection.
• The Herald newspaper of Everett, Washington, featured Once in a Blue Moon in its "FYI" column of 29^th January 1999.

Copyright 1995-2004 by David Harper and Lynne Marie Stockman
All Rights Reserved
Designed and maintained by Obliquity
Last modified on 1 September 2004
http://www.obliquity.com/astro/