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DST, finally!

March 13, 2013
Toledo Chronicle, Tama News-Herald

Sunday we changed the clocks. In my mind, this is the first step in getting all of those ducks in line for what is my favorite season-morel season, I mean spring.

The only thing I really resent about "springing forward" is that they decided to make the change at 2:00 am. I don't like having to get up THAT early just to change the clocks.

Unfortunately the hour that never was will take me a few days to catch and capture. Only then will all be right in my world. What were you doing during that hour that never was?

Article Photos

Unlike some of the winters past, we eased into winter this season. I for one was hoping we'd have a repeat of last winter. Looking at the lake in my front yard right now, I believe those visions were just that, and have since been readjusted for reality.

I love daylight saving time. Yes, it's saving, not savings! Taking the chance I might rile some of my rural neighbors, I have to admit I enjoy having more sunlight during the evening. But did you know that even without daylight saving time, we here in Iowa enjoy longer days during spring and summer than our southern cousins?

When we were kids, and school was out, mom always told us to be in by dark. Like most kids, that didn't mean sunset, but somewhere between civil and astronomical twilight. I told my kids I remember staying outside until after 10:00 in the summer, and it was still light outside! Since that doesn't happen in Florida, and my kids have been raised there, they have a hard time understanding my claim. A little bit of a stretch perhaps, but sunrise/sunset tables give credibility to my claims.

Today is March 13, 2013. (I just love it that as a columnist, I can write in the future.) Sunrise in Toledo was 7:25. Sunset will be 7:15. There will be 11:50 of sunlight today. OK, here's where it gets good. Sunrise today in SW Florida was 7:39. Sunset today will be 7:35 this evening. That gives them sunlight today of 11:56. So today, even though they are way farther south, they only have 6 more minutes of daylight than us. As the season advances, our days in Toledo get longer faster than the days in SW Florida. And by the first day of summer, on June 21, our days are markedly longer.

Let's advance the calendar a couple months and take a look at the daylight difference on that longest day of the year, June 21. In Toledo, on June 21, sunrise will be 5:35. Sunset will be 8:49. Toledo will have 15:14 of daylight on the first day of summer. Sunrise in SW Florida will be 6:35, and sunset 8:49. They will have 13:49 of daylight. On the first day of summer, the day in Toledo will be an hour and 25 minutes longer than in SW Florida! In Minneapolis, the day will be 24 minutes longer than ours, and their day will be over 15 and a half hours in length. As you march farther north, the days will be longer still, until you find the land of the midnight sun, where the sun appears to oscillate in the sky but never sets.

Why does this happen, and what dynamic causes the change of season? The earth rotates around the sun with the axis of the earth tilted 23.5 degrees with respect to the plane of the orbit, or ecliptic. As the earth makes the annual trip or orbit around the sun, the northern hemisphere is oriented more toward the sun during summer or more away from the sun during winter. During summer, when the northern hemisphere is oriented more towards the sun, the days are longer. In fact, as you move farther north, the days get longer and longer, until you reach the point where the sun never appears to set. From our perspective, here in Toledo, the summer sun appears higher in the sky than it does during the winter.

Bear in mind that the exact opposite is true during the winter months, when the northern hemisphere is oriented more away from the sun. During the winter, in the northern hemisphere, as you move farther north, the days get shorter, until you reach the point where the sun never appears to rise.

I have heard some otherwise intelligent persons explain the seasonal change by claiming the earth tips toward the sun during the summer and tips away from the sun during the winter. This tends to make one believe the earth suddenly tips on its axis one way or the other and causes the seasons. If this really happened, buildings would topple and the lakes would jump out of their banks. The earth doesn't suddenly tip on its axis!

Think of the plane of the earths orbit, or ecliptic, as a near circle drawn on a piece of paper around the sun, which is in the center of the paper. Now visualize the earth tilted 23.5 degrees on its axis, and follow the orientation of the northern hemisphere as you make an entire orbit around the sun. It's not tipping, or wobbling of the earth on its axis, but that tilt as it progresses around the sun which causes the seasons and resultant change in daylight hours.

So, now back to my statement that I remember playing outside until after 10:00 during the summer. As we all know, it doesn't suddenly get dark when the sun sets. We have a certain period of twilight, during those minutes after sunset commonly called dusk. There are generally 3 different accepted definitions of twilight: civil, nautical, and astronomical. The definitions of each type of twilight are the sun is 6, 12, and 18 degrees below the horizon respectively.

Complete darkness ends sometime after the end of evening civil twilight. The horizon is clearly defined, yet the brightest stars, and possibly Venus are visible. Nautical twilight light conditions find ground objects still distinguishable, but the horizon is not defined. We all thought that is what mom meant by "being inside before dark." Astronomical twilight finds sky illumination almost imperceptible. That is the time astronomers might break out their telescopes, and my mom expected us to already be inside.

The US Naval Observatory maintains a web site where you can find tables for sunrise/sunset for any place on earth, including the 3 forms of twilight. You can do your own research on this site.

aa.usno.navy.mil/data/docs/RS_OneYear.html

According to this site, on June 21, in Toledo, sunset is 8:49. Civil twilight ends at 9:24, and nautical twilight ends at 10:08!

My statement might have been something of a stretch, but it's my story and I'm sticking to it! The Naval Observatory supports my stand!

Until next time-

You can read past columns by visiting tamatoledonews.com and clicking on the "Local Columns" button.

In to the Wind and this column are copyright 2005 - 2013 Mike Gilchrist. Readers, feel free to contact me at mike@aweiowa.com via email, or write to me at P.O. Box 255, Toledo, IA 52342.

 
 

 

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