RadioBDC Logo
Would You Fight For My Love | Jack White Listen Live
 
 
< Back to front page Text size +

More light as we head towards spring

Posted by David Epstein  January 27, 2012 06:19 PM

E-mail this article

Invalid E-mail address
Invalid E-mail address

Sending your article

I hope you will enjoy our late January weather this weekend with sunshine and mild temperatures. As we close out the month of January one of the biggest changes you are probably noticing is the increase in light at the end of the day. As the earth continues its journey around the sun we are seeing the daylight rapidly increasing. It's not just the light itself that is increasing, so too is the position of the sun throughout the day. For me, the sun's angle and how it increases this time of the year, is as remarkable as the increase in daylight itself.

Around December 21st, the first day of winter, the sun at noon is about 24 degrees off the horizon. Think of that number this way. If the sun is at 90 degrees off the horizon at noon, it's directly over your head. At sunset, the sun is at zero degrees as it hits the horizon. With this in mind, the sun at 45 degrees off the horizon, is halfway from your head to your feet. In December the sun is very low off the ground the entire day never getting above 25 degrees off the ground. This is one of the reason's our shadows are so long in the winter. sun angle seasonal.jpgThe low angle is also why the light looks different. In winter, the sun's rays have to pass through more atmosphere to get here so the light is not as pure as in the heat of summer. Here is what I find really cool. On June 21st, the sun's rays are at about 71 degrees above the horizon. That is an increase of over 45 degrees from December and why in summer at noon your shadow is so short . This weekend, the sun will already be 6 degrees higher at noon than it was back in December. By the end of February, the sun will be another 10 degrees higher at around 40 degrees off the horizon. At that time of year, if we do get any snow, the increase in the suns angle is why the snow melts so much faster. Temperature also plays a role with melting, but the sun's angle is also quite important.

By summer our days are at their longest. In the some parts of the world, like northern Alaska, the sun is up for 24 hours in the summer. However, the angle there is still quite low. For example, around Barrow, Alaska in June the sun is still under 40 degrees even at noon. midnight sun.jpg In other words, the highest the sun gets around the arctic circle in summer is about the same as we see in March. If you do want to the sun directly over head, at 90 degrees, you can go to the equator on the first day of spring or fall. I was very close to the equator several years ago on the first day of spring. Other people on the cruise were not as excited as I was about the sun directly overhead at noon. I am kind of a geek that way.

It's not only the angle up and down that is rapidly changing. Yes, the sun rises in the east and sets in the west. However, not exactly. In the winter the sun rises south of due east and in the summer it rises north of due east. In winter the sun sets south of due west and in the summer it sets north of due west. This is one of the reason's solar glare is a factor at certain times of the year and not others. For example, on the 21st December, the sun will rise 68° east of due south and set 68° west of due south.compass.jpg On the 21st March/21st September, the sun will rise 91° east of due south and set 91° west of due south. On the 21st June, the sun will rise 114° east of due south and set 114° west of due south.

Finally, our entire hemisphere is starting to tilt back towards the sun. If you have never understood how the northern hemisphere faces the sun during part of the year and away during the other, try this little exercise. seasons.jpg Make a fist with your left hand. Go ahead, no one is looking. OK, good. Now take your right hand and stick up your pointer finger, the one next to your thumb. Great. Angle it so your finger print side is pointed towards your other hand, the sun. That is summer. Now move your right hand counter clockwise(toward the left) around your left hand. Notice the finger print side of your finger is now facing away from the sun. That is winter. I use this example when I speak to schools about the seasons. Kids love it.

So enjoy the added light this weekend. Our sun will be setting a few minutes before five this weekend and by next weekend will be enjoying over 10 hours of daylight for the first time since early November. Sunrises are still just after 7 a.m. as we gain morning light a bit differently. That topic will be great for another blog. Winter weather isn't over, but spring light is surely coming.


Follow me on Twitter at @growingwisdom and check out my latest videos at GrowingWisdom.com

This blog is not written or edited by Boston.com or the Boston Globe.
The author is solely responsible for the content.

E-mail this article

Invalid E-mail address
Invalid E-mail address

Sending your article

 

About the author

David Epstein has been a professional meteorologist and horticulturalist for three decades. David spent 16 years at WCVB in Boston and currently freelances for WGME in Portland, ME. In 2006, More »
Boston Forecast & Weather Tracker - Storm Center
Get complete Boston snow and weather coverage here.

Get updates on Twitter

More community voices

Child in Mind

Corner Kicks

Dirty Old Boston

Mortal Matters

On Deck

TEDx Beacon Street

archives