Expert: Ed - 1/5/2007

Question
Hello Ed
The sunrise and sunset times issued for Dublin, Ireland show that during March the sun will rise 11 minutes earlier at the end of the month than the beginning, but the sun will set nearly 2 hours later at the end of March than at the beginning. I'd have thought that the day would stretch equally at both ends of the day as summer approaches, but it seems it doesn’t go like that. Do you know why?

Answer
John,

You're right, that is odd.  Unfortunately, the answer is pretty boring.  It's just because that's the month that we've all agreed to begin Daylight Savings Time.

This website should help you to follow what I'm saying, if you want to open up another window:
http://www.timeanddate.com/worldclock/astronomy.html?n=78&month=3&year=2007&obj=...

Think about it.  As we move from winter to summer, the sunset gets later every day, and the sunrise gets earlier every day.

Suddenly, on March 25, we "spring forward."  So, we set our clocks ahead, by one hour.  This means that the sunset time, which would have been 6:47, is 7:47 instead.  Therefore, for the month of March as a whole, the sunset time APPEARS to move ahead by one hour and 56 minutes.  In reality, it only changes by 56 minutes.

Similarly, the time of sunrise gets earlier every morning.  When you set the clocks ahead on March 25, the sunrise would have been at 6:17 AM, but instead it's suddenly at 7:17 AM.  Over the course of the entire month of March, the sunrise would have moved back by about an hour, but because of daylight savings it actually almost evens out, and rises at almost the same time at the end of March as it does at the beginning.

I hope this is helpful.  Keep Looking Up!
--Ed