Do places at the same lattitude have equal length of daytime on the same day irrespective of their longitude. I have a debate about this with a Japanese friend who claims that days at 52 degrees North in Japan have a different time between sunrise and sunset then Amsterdam at 52 degraas North. A good bottle of champagne is at stake so I would like to find out!!

Thank you very much,

Wouter Dammers

-- Wouter Dammers (w.dammers@tregout.nl), March 26, 2001

Answers

Wouter

I was inclined to say the day length is equal - but I checked using the SkyMap Pro ephemeris feature and got results a little different to my expectations.

So, some questions for you

- Are the two locations at similar distances from the time zone meridian?

- Does the day length have to be identical _all_ year?

I think the main difference might be because Japan sees a Sun with a very slightly different declination from the Sun as seen from Europe. Their sunrise will be 9 hours earlier, that's 9 / (365.25 * 24) or 0.001 of a year. In that time, the Sun would change declination by roughly 0.097 degrees, or 6 arcminutes. This is about one fifth of the disc of the Sun, so you might see a small change in day length???

-- Keith Burnett (kburnett@btinternet.com), March 26, 2001.