Happy Autumnal Equinox! I am writing this on one of the four key dates in the solar calendar, the September Equinox. Follow me below the orange Analemma for more details. First, a word from the IAN files:
As you can see by Itzl's concerned look, this group gives Kossacks a safe place to check in, a daily diary where we can let people know we are alive, doing OK, and not affected by such things as heat, blizzards, floods, wild fires, hurricanes, tornadoes, power outages, earthquakes, or other such things that could keep us off DKos. It also allows us to find other Kossacks nearby for in-person checks when other methods of communication fail - a buddy system. If you're not here, or anywhere else on DKos, and there are adverse conditions in your area (floods, heatwaves, hurricanes, earthquakes etc.), we and your buddy are going to check up on you. If you are going to be away from your computer for a day or a week, let us know here. We care!
IAN is a great group to join, and a good place to learn to write diaries. Drop one of us a Kosmail and ask to be added to the Itzl Alert Network anytime! We all share the publishing duties, and we welcome everyone who reads IAN to write diaries for the group! Every member is an editor, so anyone can take a turn when they have something to say, photos and music to share, a cause to promote or news!
We do have a diary schedule. But, when you are ready to write that diary, either post in thread or send FloridaSNMOM a Kosmail with the date. If you need someone to fill in, ditto. FloridaSNMOM is here on and off through the day usually from around 9:30 or 10 am eastern to around 11 pm eastern.
Monday:
BadKitties
Tuesday:
ejoanna
Wednesday:
Caedy
Thursday:
art ah zen
Friday:
FloridaSNMOM
Saturday:
Most Awesome Nana
Sunday:
loggersbrat
Because of the elliptical rotation of the Earth around the Sun (glad we got that fact established finally! Thank you, Nicolaus Copernicus!) we have seasons (hooray!) Four dates in our calendar year mark the onset of another season. Which season? Depends on whether you are in the Northern or Southern Hemisphere. And where the "sub-solar point" is. Uh-oh, This is getting complicated. Or is it?
Let's sketch this out.
As you can see in the diagram above the orange squiggle, "equinox" literally means "equal night." There are 2 Equinoxes in the year: one the third week of March; the other the third week of September. On these dates, the "sub-solar point", the point where at noon the sun appears to be directly overhead (at a 90°angle), is at the Equator. Thus the hours of day and night are equal at every latitude on the Earth. The next day, though, the balance of daylight hours to nighttime hours begins to shift, again, depending on where you are, north or south of the Equator.
Here's another image of Equinox:
Here in the Northern Hemisphere (NH), the day after Equinox the sub-solar point begins its move into the Southern Hemisphere (SH). So, north of the Equator, our daylight hours decline and night time hours increase. This is our Autumn. In the SH, just the opposite. Their day light hours begin to increase and their hours of night begin to decrease. For the SH, Spring has begun.
Again, all this courtesy of the earth's oval-ish rotation around the sun.
I said earlier that there are 4 of these "seasonal gateway" dates in a year. What are the other two? They are the "Solstices", the 2 dates of the most extreme unequal day and night hours at any location. Again, this is because of the position of the Earth vis-a-vis the Sun, the third week of December and the third week of June: the onset of Winter and Summer, depending on which hemisphere, north or south. I'll save the details on the Solstice for December. . .
Finally, what the heck is an Analemma? It's a chart, really, that appears on many older maps and globes:
It tells us where the sub-solar point is on any given day of the year. And by "where" I mean at what latitude on the globe. Neat, huh?
When I taught college level Physical Geography, I loved the section on the seasons. And loved it as an opportunity to urge students not to be "chauvinistic" about the Northern Hemisphere. After all, not everyone lives there, despite our bias. And our map bias, too.
Sometimes we need a different view:
But as most of us IAN-ites are in the North, I'll wish you a Happy Autumn!