Terry's Astronomy Thread.

[Bluearrowll]

What's in the sky tonight?
December 21, 2013

-Today is the shortest day of the year in the Northern Hemisphere; the longest day in the Southern Hemisphere. Winter in the north, and summer in the south, begins at the solstice: 12:11 p.m. Eastern Standard Time. This is when the Sun reaches its farthest point south for the year and begins its six-month northward return. Happy Yule.

-If there's one constellation that everyone should know at this time of year, it's wintry Orion climbing up in the east-southeast. As always when Orion is on the rise, the three-star Belt of Orion in its middle is nearly vertical. Show someone Orion this week and they'll know it for a lifetime.

-On Dec. 19th, the European Space Agency launched one of the most ambitious astronomy missions ever: GAIA, an observatory that will survey more than one billion stars in the Milky Way. By the time GAIA's five year mission is over, astronomers will be able to build the first accurate three-dimensional map of celestial objects in our home galaxy. GAIA will do its work from the L2 Lagrange point approximately 1.5 million km from Earth. On Dec. 20th, amateur astronomer Dave Eagle of Higham Ferrers UK observed the spacecraft hurtling toward that distant station.

"It was great to see the spacecraft in the exact position predicted, near the shield of Orion," says Eagle. "After watching the launch live on the Web in the morning, I was glad to be able to track it down and wish it well in its coming mission. It was much brighter than I expected, so its newly deployed Sun shield is doing a great job."

Once it reaches its L2 parking orbit and begins observing, GAIA will log the position, brightness and color of every star that falls within its field of view. By repeating these observations throughout its mission, astronomers will be able to calculate the distance, speed and direction of motion of each star GAIA sees, chart variations in their brightness, and determine whether they have nearby companions. This kind of detailed information about the Milky Way is unprecedented and may lead to important new discoveries about the evolution and structure of our galaxy. For updates about GAIA, stay tuned to the ESA. http://www.spaceweather.com/images20...a.20131219.avi

Astro Picture of the Day:
December 21, 2013

Source:
Today, the solstice is at 17:11 Universal Time, the Sun reaching the southernmost declination in its yearly journey through planet Earth's sky. The December solstice marks the astronomical beginning of winter in the northern hemisphere and summer in the south. To celebrate, explore this creative visualization of the Sun from visible to extreme ultraviolet wavelengths, using image data from the orbiting Solar Dynamics Observatory (SDO). Against a base image made at a visible wavelengths, the wedge-shaped segments show the solar disk at increasingly shorter ultraviolet and extreme ultraviolet wavelengths. Shown in false-color and rotating in a clockwise direction, the filters decrease in wavelength from 170 nanometers (in pink) through 9.4 nanometers (green). At shorter wavelengths, the altitude and temperature of the regions revealed in the solar atmosphere tend to increase. Bright at visible wavelengths, the solar photosphere looks darker in the ultraviolet, but sunspots glow and bright plasma traces looping magnetic fields. Watch the filters sweep around the solar disk in this animation of SDO's multiwavelength view of the Sun. http://svs.gsfc.nasa.gov/vis/a010000/a011300/a011385/