Do days get shorter in Seattle during the winter?

July 16, 2005 10:30 PM

Does the American Pacific Northwest get less daytime in the winter than in the summer, and if so, why?

I'm not just talking about sunlight. I'm talking about the amount of time per day that the sun is actually 'up,' whether you can see it or not. Doesn't this have something to do with the angle of the Earth's axis and the latitude of the region? Doesn't something similar (but more extreme) happen in Norway, or is that a totally different phenomenon?

posted by bingo to science & nature (15 comments total)

It's not just the Pacific Northwest that gets less daytime--the higher in latitude in the northern hemisphere you go, the more day time you have as you approach the summer solstice (the longest day of the year for folks in the northern hemisphere). Similarly, in the southern hemisphere, the lower in latitude you are, the more daylight you'll have as you approach the winter solstice.

Wikipedia on:
Summer Solstice
Seasons
posted by scalespace at 10:46 PM on July 16, 2005

I'm in Alaska right now - and I'll tell you, it definitely does. It's 10:00 PM, and still broad daylight, as a matter of fact, it won't be getting dark tonight.
posted by Dag Maggot at 11:06 PM on July 16, 2005

It's caused by the Earth axis being tilted in relation to its orbit around the Sun.

Northern Hemisphere summer
Northern Hemisphere winter
posted by 517 at 11:50 PM on July 16, 2005

Picture in your head the earth in orbit around the sun. The earth is spinning on it's axis. Now illuminate the half of the earth that is facing the sun. If the axis is perfectly vertical (perpendicular to the orbital plane), all parts of the earth will get equal sun and darkness always as the earth rotates in place, and where it is on its orbit will make no difference.

Now, with the mental simulation still running, tilt the earth's axis. See the difference?

Now if the tilt always faced the sun (much like how the same side of the moon always facing earth as it orbits), that difference would remain constant - one hemispere would always get less sun than dark (ie permanently in winter), while the opposite would always be getting more sun than dark (ie permanently in summer). But the tilt doesn't face the sun as the earth orbits, it always faces the same direction no matter where in the orbital path the earth is. So it takes a full year before the seasons repeat.

Since this mental orrery is up and running, no sense wasting it - once you've wrapped your head around seasons, add the moon to the mental simulation, and work out why you can often see the moon during the day, but never a full moon. (A full moon is visible at night only). :)
posted by -harlequin- at 4:31 AM on July 17, 2005

I used to live in Seattle and because of its latitude you can actually grow things on the north side of buildings (i.e. the north side actually gets light).
posted by Taken Outtacontext at 5:27 AM on July 17, 2005

times of sunrise and sunset in seattle
posted by pyramid termite at 6:11 AM on July 17, 2005

Thanks for all the answers so far. Does anyone know if the sunrise calculator at almanac.com takes daylight savings time into consideration, or if it needs to be added? And are there any charts similar to pyramid termite's, but for Portland, Or?
posted by bingo at 6:26 AM on July 17, 2005

world sunlight map Two semi-realistic renderings of the world showing sunlit area and current cloud cover. You can see how the northern hemisphere is tilted.
posted by jjj606 at 8:51 AM on July 17, 2005

I'm not sure I buy that, TO: Seattle is farther north than Chicago. It probably has more to do with the perpetually overcast sky acting as a giant diffuser, illuminating the ground from all angles.
posted by Eamon at 9:05 AM on July 17, 2005

This site should give you sunrise & sunset times for Portland, at least on a month-by-month basis. I found it by searching for "portland oregon sunrise sunset times" on Google. As for the Old Farmer's Almanac page, the results I get specifically say "all times are Pacific Daylight Time", so you shouldn't need to correct them.
posted by Johnny Assay at 9:31 AM on July 17, 2005

So, seriously not to snark ... but how did you grow up not knowing this? Are the places in the US where the days are all the same length? I'm in the UK, and have known since I was self-aware that the days are longer in summer.
posted by bonaldi at 10:57 AM on July 17, 2005

The UK is at approximately 50 degree latitude. The US is generally at 40 degrees and lower (I'm at 33.7 degrees and I'm not in the extreme south). The effect is much more dramatic and obvious to folks Northern Europe than it is to us in the U.S.

On a related note, I was stunned at how fast the sun set when I was in Colombia -- at the equator. It was like there was little warning, i.e. no dusky period. It just went from light to dark in like 15 minutes. Bam!
posted by intermod at 11:38 AM on July 17, 2005

Bingo's profile says he's in NYC, which is around 40 45' north (only seven degrees south of Seattle), and the day length there varies by about five and a half hours between summer and winter. (According to xephem, at least.)
posted by hattifattener at 11:53 AM on July 17, 2005

So, seriously not to snark ... but how did you grow up not knowing this?

I grew up in Kansas, where the difference is not as obvious, and later moved to Seattle, where it was. As you can see from my question, I did understand the general idea, even if I couldn't quite explain it. Last night I was discussing this with someone who grew up in Portland, and that person insisted that the days there are shorter in the non-summer because the sun is blocked by the rain and clouds. I googled but could not find an explanation that directly addressed the issue, so I decided to ask about it here. I have emailed the person (non-mefite) a link to this thread. So, it's not that I didn't know per se; I just wanted to state the question with relative neutrality.
posted by bingo at 2:08 PM on July 17, 2005

Scalespace said:
Similarly, in the southern hemisphere, the lower in latitude you are, the more daylight you'll have as you approach the winter solstice.

Just to be picky, the days are not longer in the southern hemisphere at winter solstice. Winter solstice, as everyone knows down here, is in June, and y'all up there are backwards. :-P

The weird thing in Europe (from an American view) is the daylight changes are much more extreme than the US, even though the climate is deceptively milder. Counter-intuitive.
posted by Goofyy at 12:06 AM on July 18, 2005