Weather Blog

No, our sunset chart isn't broken...

No, our sunset chart isn't broken...
We have a saying in the news business along the lines of "Don't you hate it when the facts get in the way of a good story?"  There are many times we hear something on the police scanner that sounds really big, news-wise, only to find it was nothing. (Good example today of a report of shots heard outside a Wallingford post office, only to find out it was someone moving an old beat-up truck and it was backfiring.)

So here I was set today to write my blog entry about how our sunset chart isn't broken because it shows the sun setting earlier now before the solstice date of June 20th.  Only to find out, for this year, sunrise and sunset charts do pretty much show the longest day of the year is indeed June 20th.

Instead, let's pretend it's December -- not too hard to do if you've been reading my earlier blog entries about how this month has been as cloudy as last December. Look at the sunrise/sunset chart here: http://bimedia.ftp.clickability.com/fishwebftp/KOMO/sunset_table.jpg

Note how the winter solstice is December 21 (at 4:04 a.m.) and that makes it the shortest day of the year, daylight wise. But on the chart, the earliest sunset is on December 16 (4:16 p.m. PST) and the latest sunrise is on January 4th.  How can that be?

And thus, we've come to the original point of the blog entry -- to talk about this really complex topic called "The Equation of Time".  

Earth's path around the sun isn't a circle, it's an ellipse. We orbit faster around the sun in winter when we're closest, and slowest when were furthest away in summer. These little changes mean the sun is not at its highest point in the sky when we say it's noon -- it can be off a few minutes.

OK, I've tried in my head to turn the rest into plain English, but my notes are a mess, so maybe best to have you just read this article for more info:

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980116c.html

Now, on to something more simple: The U.S Naval Observatory has a great site to track all sorts of fun stuff like sunrise tables and Moon sets, etc. But one of the most useful is this list of when the seasons begin:

http://aa.usno.navy.mil/data/docs/EarthSeasons.php

Those times are listed in GMT time, so for winter, you subtract 8 hours. For the other three seasons when we're on Daylight Saving Time, you subtract 7 hours. Note that sometimes that makes it a day earlier. For instance, this spring officially began May 20 at 5:48 a.m. GMT but that is May 19th at 10:48 pm here in Seattle.

Here is where you can get a sunrise/sunset chart for anywhere!

http://aa.usno.navy.mil/data/docs/RS_OneDay.php


The caveat here is that these charts are all for Standard Time. So add one hour for PDT.  This is also on the 24 hour clock, so for sunsets, subtract 12 if you are more comfortable on the usual 12 hour clock. (For example, the sunset today is 20:11, but add an hour for PDT, so it's 21:11, and then subtract 12 and it's 9:11 p.m.)