Monday, November 26, 2012

Chile: Summer and Winter


I've now spent over a year in Chile and have taken pictures from time to time. Here I present two pairs of pictures of approximately the same location, but shifted in time by several months. That is, one picture is taken around Summer, while the other was taken around Winter (or close enough). This showcases how the seasons change here in Santiago and it's a good opportunity to talk about how the seasons work on Earth.

As always, remember that you can click the pictures to see them larger.
More details, and the second picture, after the jump.

The first pair of images you can see above was taken in Cerro Calan, on the road to work. The image on the left was taken on August 16, well into Winter and almost into Spring. The image on the right was taken more recently, on November 15-- clearly Spring (and nearly Summer). The time of day is different, but the lighting conditions are similar so I think this pair is adequate for comparison.

You can tell that it rains more frequently in the Winter months given the very green grass and the snow in the mountains. The air is crisp and clear thanks to the frequent rain showers (but smoggy if it doesn't rain). On the right, you can see the grass is yellower thanks to the drier conditions during Summer. Given the proximity to Spring, flowers are very much evident. The flowers will eventually disappear and the grass will get yellower as conditions dry up. Notice also the tree on the left in both panels. In Winter, the leaves are gone but they have returned by Summer. Though the smog is not as bad in the Summer, winds can pick up loose dust and cause the haziness you can see on the horizon. Snow is also no longer evident on the mountains.

The next set of pictures is shown below. The one on the left was taken on June 21, while the one on the right was taken on November 23. The time of day is, again, not the same.
The most striking feature you notice will be the snow-capped mountains on the Winter picture at left. The sharp detail you can see can be due to the lighting as the image on the left was taken in the morning. The image on the right was taken in the afternoon (the Sun's glare prevented a morning shot). Another interesting feature is the foliage on the trees. Those on the left are either bare or with orange/brown leaves (baring a few exceptions, like evergreens), while those on the right are full of green leaves. The grass in this area is irrigated so it does not get as noticeably dry as up in Cerro Calan.
If you look carefully at the buildings, you may notice that on the far left there is a pair of buildings under construction. Five months later, the buildings are nearly complete with most of the glass panels in place.


If you've read closely thus far, you may realize something odd, particularly if you've grown up in the Northern Hemisphere (statistic-wise, the majority of my readers are in the US). I've been calling dates around June and August "Winter" and those in November "Summer." As most people probably know, the seasons are flipped between Northern and Southern Hemispheres. When it's Winter in the US, it's Summer in Chile. Many times, people refer to the southern versions as "austral," so we are now entering austral Summer. In the US, people are getting ready for boreal Winter.

Why are the seasons flipped?
This is easy to understand if you know how the seasons work. A common misconception is that the seasons are caused by the distance between the Earth and the Sun, but this is incorrect. If that were the case, then both hemispheres would experience Summer and Winter at the same time.
The true cause of the seasons is due to the tilt of Earth's axis. Have a look at this diagram:
The Earth at two positions on its orbit around the Sun. Not to scale. Credit.

The Earth's axis is tilted by 23.5 degrees; it does not point straight out of the plane of the solar system. Parts of the year, the North Pole of the Earth's axis will point slightly more towards the Sun. During that time, more light falls unto the Northern Hemisphere than the Southern one. The Sun appears higher in the sky, the amount of daylight is longer, and conditions become warmer there: the North experiences Summer. The opposite occurs in the South, which experiences Winter. The reverse happens when the axis points away from the Sun, 6 months later: Winter in the North, Summer in the South.

Exactly how hot or cold or rainy or dry things become will depend on the exact conditions on where you are. For example, a coastal area's seasons can be markedly different than places at high altitude.
Regardless of where you live, take a moment out of your day and look around you. If you pay attention, you can see how things change through the year on the Earth we live in.

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