Cosmic Log - winter

Dec

2011

9:22pm, EST

Holiday calendar: Season's tiltings

This picture of Earth was taken at 06:00 GMT on Dec. 21 by Eumetsat's Meteosat-9, a meteorological satellite that is stationed in geosynchronous orbit above a point close to Africa's west coast. The picture illustrates how Earth's tilt with respect to the sun creates the darkest night of the year for the Northern Hemisphere, and the longest stretch of daylight for the Southern Hemisphere.

By Alan Boyle, Science Editor, NBC News

Tonight is the longest night of the year for the Northern Hemisphere, due to the winter solstice. The season officially changes from autumn to winter at 12:30 a.m. ET Thursday ... unless you're south of the equator. In that case, spring is turning to summer.

You probably learned in school why the seasons (and the temperatures) change during the course of the year, but in case you need a refresher on how the 23.5-degree tilt of Earth's axis affects the weather, we have the full story for you. This picture, snapped by Eumetsat's Meteosat-9 weather satellite today, shows the situation graphically.

Meteosat-9 is camped out in a geosynchronous orbit that puts it precisely above an equatorial point on the west coast of Africa. Every day at around 6 a.m. local time, it has a great view of the terminator line between day and night, cutting straight across Earth's disk. The slant of that line changes from day to day, due to the changing orientation of Earth's tilted axis with respect to the sun.

On the day of the December solstice, the slant is at its most extreme angle, leaving the north pole in the dark while exposing the south pole to 24 hours of daylight. That's what you're seeing in the photo above. National borders and crosshairs have been added to help you get oriented properly.

This video, put together by NASA's Goddard Space Flight Center, shows you how the slant changes from one September equinox to the next:

A NASA compilation of Meteosat imagery shows how Earth's terminator line between day and night changes over the course of a year.

If you check out Eumetsat's near-real-time imagery from Meteosat-9 for 1 a.m. ET (06:00 GMT) Thursday, you can see the solstice effect pretty much at its peak. These pictures of the shifting seasons serve as tonight's offering from the Cosmic Log Space Advent Calendar, which has been featuring daily images of Earth from space during the run-up to Christmas. Feel free to click through these previous images in the series, and check back on Thursday for another satellite image that will take the edge off winter.

Alan Boyle is msnbc.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. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Dec

2010

12:37pm, EST

NASA

A NASA satellite image shows the reach of a massive snowstorm that blanketed much of the Midwestern U.S. last weekend.

Holiday calendar: White Christmas in the Midwest

By John Roach, Contributing Writer, NBC News

Dreaming of a White Christmas? This satellite image shows what it would look like from more than 400 miles up. The picture, snapped on Sunday by NASA's Terra satellite, shows the aftermath of a massive snowstorm that walloped the Midwestern U.S. last weekend before wreaking havoc further east.

Although snowy weather is the norm this time of year in the Midwest, this one was a monster. The 17.1 inches of white stuff measured at the Twin Cities International Airport in Minnesota set a record for the largest December storm in the Minneapolis/St. Paul region and was the fifth-largest snowstorm ever recorded in the state, according to the state's climatology office.

Minnesota wasn't the only state impacted by the winter blast. A significant part of about a dozen states can be seen blanketed in snow in this true-color image by Terra's Moderate Resolution Imaging Spectrometer, or MODIS.

The storm, for football fans at least, will be most remembered for causing the collapse of the inflatable roof on the Metrodome, home to the NFL's Minnesota Vikings. The incident forced a planned Sunday game between the Vikings and the New York Giants to be moved to Monday night in Detroit. The Vikings lost, 21-3.

Terra's big-picture view of the storm is part of the Cosmic Log Space Advent Calendar, which is highlighting images of Earth from space every day until Christmas. For more Advent calendar goodies, check out the Web links below:

Connect with the Cosmic Log community by hitting the "like" button on the Cosmic Log Facebook page or following msnbc.com's science editor, Alan Boyle, on Twitter (@b0yle).

Snowflakes take the prize

Caltech physicist Ken Libbrecht deals with gravity-wave detectors, tunable diode lasers and nanoscale crystal growth, but his biggest claim to fame is snowflakes. How many other physicists can brag that their work has been printed on postage stamps? Not that Libbrecht is the kind of person to brag, but if he was, he'd have one more thing to brag about: Sweden's Lennart Nilsson Award, a 100,000-kronor ($15,000) prize given annually to honor scientific and medical photography.

"Kenneth Libbrecht's images open our eyes to the regularity and beauty of nature," the board said in its citation. "With his photographs of snowflakes, he turns mathematics, physics and chemistry into images of great beauty."

Over the years, Libbrecht has perfected his formula for capturing the microscopic crystalline structure of frozen water in photographs -- to the point that he's authored several books on the subject. His recipe for preserving snowflakes on a microscope slide, involving a "1 percent solution of polyvinyl acetal resin," even made it into the script for an episode of "The Big Bang Theory" on prime-time television.

Probably one of the most often asked questions he faces is a classic: "Is it true that no two snowflakes are alike?" He provides the most reasonable answer: No two snowflakes are exactly alike, but they can look alike. (Other researchers have taken a similar stance.)

Libbrecht is due to pick up his award next week at Berwald Hall in Stockholm, with Swedish photographer Lennart Nilsson himself in attendance. The Swedish Postal Service will also be issuing a set of Libbrecht snowflake stamps next month. Some parts of Sweden can be pretty chilly this time of year, but it's nice to know the Swedes are giving the king of snowflakes a warm reception.

More about snowflakes and winter:

Visit the Cosmic Log page on Facebook and hit the "Like" button. You can also follow @boyle on Twitter. And if you really want to be friendly, ask me about "The Case for Pluto."