Today is the Winter Solstice, the shortest day of the year for us living in the Northern Hemisphere. While the seasons are not as important as they were hundreds or thousands of years ago (for non-farmers anyway), season changes always are headline news.
So, why do we have seasons, anyway?
It's all about Earth's tilt. If the Earth were spinning on its axis with no tilt at all, everyone would be treated to days of identical length every day of the year, with latitudes nearer the equator having longer days than those nearer the poles. However, with the tilt, the angle of the Earth relative to the Sun changes as or planet moves about its orbit. On the Winter Solstice (today) the Northern Hemisphere is tilted up and away from the Sun. On the Summer Solstice, the Northern Hemisphere will be tilted down toward the Sun. On the equinoxes, the tilt is half way between the solstices. To see this effect, go out and observe the path the Sun takes through the sky for the course of day of winter).
As seen on the Winter Solstice from the Cleveland area, the Sun rises in the Southeast, arcs low in the Southern sky, peaking at a height of about 25 degrees at local noon (about 12:30pm), and then starts heading down to its set in the Southwest. On the solstice, the day will be over 9 hours long. Now, for people living at different latitudes, your numbers may differ with more Northerly dwellers seeing more extreme changes. For about a month after the solstice, you will notice that the rise/set points of the Sun hardly change, hence “solstice” from the Latin words “sol” and “sitre,” literally, “Sun stands still.”
By early February though, the days start to lengthen noticeably as the Sun is moving North, towards due West at sunset. The lengthening of the days will accelerate until the Sun reaches the day of the Vernal Equinox, where it will rise/set exactly due East/West. At this point, both day and night will be exactly 12 hours long. The Sun will never leave the Northern celestial hemisphere until the Autumnal Equinox (first day of fall).
The lengthening of the days will continue until the Sun finally reaches its most Northerly rise/set on the Summer Solstice, the longest day of the year. On this day, the Sun will rise/set low in the Northeast, get about 72 degrees high at local noon (about 1:30pm in Cleveland thanks to a return to Daylight Savings Time). The final result: a day that is over 15 hours long.
So there they are, the reasons for the seasons.
Like this?
Hit the 'subscribe' button for automatic email updates when I write something new!
Want to read more of my stuff? Check out my other Examiner columns!
Photography Examiner
Cleveland Astronomy Examiner
Cleveland Photography Examiner
Space News
ESA gives up on Phobos-Grunt
Most Earth-like planet yet
Get psyched for upcoming eclipse
Saturday's eclipse, what you can see
Why tomorrow's eclipse is 'impossible'
Want even more? Check out my personal website:
Bodzash Photography and Astronomy
Comments