PhotoBlog - seasons

Mar

2013

6:55pm, EDT

GOES satellite sees Earth at equinox

NOAA

The GOES-13 satellite captured this full-disk image of our planet at 7:45 a.m. ET on March 20, just after the 7:02 a.m. ET equinox. The satellite image shows how Earth's two hemispheres receive equal amounts of sunlight during the equinox. In this image, the sun is artificially created to enhance the picture.

By Alan Boyle, Science Editor, NBC News

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Earth's 23.5-degree tilt almost always ensures that the northern and the southern halves of our planet get unequal amounts of solar energy, with longer nights in winter and bigger stretches of sunlight in summer. Twice a year, however, both hemispheres get equal amounts of light, with equal intervals of day and night. That's what's known as the equinox.

Just such an event at 7:02 a.m. ET on Wednesday heralded the official beginning of spring in the Northern Hemisphere, and the start of autumn in the South. This full-disk picture from the GOES-13 weather satellite, captured at 7:45 a.m., shows the equal division between Earth's night and day.

"The visible imagery sensor on GOES requires sunlight to 'see' clouds, and so it provides a useful example of the equinox," the National Oceanic and Atmospheric Administration's Environmental Visualization Laboratory says in Wednesday's advisory. "In this image the GOES imagery extends to each of the poles since the entire hemisphere is equally lit. After the equinox passes today, the Northern Hemisphere will be more lit than the Southern Hemisphere – causing the seasons."

Orbital mechanics may determine the precise moment of the equinox, but scientists say that the effects of the seasonal change can vary widely, due to climatic factors. There's some evidence, for example, that climate change is causing flowers to bloom earlier in the eastern U.S. than they did in the 1850s or the 1930s. Have you noticed changes on shorter time scales? Feel free to spring into action with your comments below.

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More about the changing seasons:

Tip o' the Log to LiveScience's Douglas Main.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log and the rest of NBCNews.com's science and space coverage, sign up for the Tech & Science newsletter, delivered to your email in-box. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Sep

2011

7:25pm, EDT

Watch Earth's seasons change ... in 12 seconds

Watch an 11-second satellite video that tracks Earth's shifting orientation with respect to the sun, through northern autumn, winter, spring, summer and back to autumn. (Credit: NASA / EUMETSAT)

By Alan Boyle, Science Editor, NBC News

In the wake of last week's equinox, the days are shorter than the nights in the Northern Hemisphere, and longer in the south. Every day from now until December will increase the imbalance. How does that happen? It has to do with Earth's changing tilt with respect to the sun, as explained in this tutorial. But sometimes a moving picture can be worth a thousand words.

This 12-second video clip has been assembled from a year's worth of imagery captured by a visible-light and infrared camera on EUMETSAT's Meteosat-9 satellite. Meteosat-9, like other satellites in geosynchronous orbit, has an unchanging view of Earth from a height of about 22,000 miles. Every day, around 6 a.m. local time, the satellite watches the terminator line between night and day move across Africa.

As it spins, Earth is tipped 23.5 degrees on its axis relative to the sun, with the northern point of the axis pointing away from the sun in December and pointing toward the sun in June. That means the Northern Hemisphere is more shadowed in winter and more sunlit in summer. That back-and-forth shift is exactly what you're seeing in the video. At the midpoints between those extremes — for instance, last week's equinox — the terminator line goes straight down the middle of Earth's disk, as seen by Meteosat-9.

Click on over to our tutorial or NASA's Earth Observatory posting to learn more about the changing seasons, as seen from space. And if you're still scratching your head over Earth's tilt, check out this video:

This video explains how Earth's tilt affects the seasons.

More views of Earth from space:

Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding me to your Google+ circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.

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GOES satellite sees Earth at equinox

One tree, four seasons

Watch Earth's seasons change ... in 12 seconds

In Vermont, two seasons for the price of one