NATIONAL GEOGRAPHIC'S SPACE PICTURES THIS WEEK XLV

Space Pictures This Week: Solar Tantrum, Petroglyphs at Night
By National Geographic News, 22 January 2013.

The sun throws a tantrum and Beijing is swathed in air pollution in the latest space pictures.

1. Forecast: Cloudy

A camera on the International Space Station (ISS) snapped this shot of stratocumulus clouds, released on January 4, as the ISS passed over the Pacific Ocean, flying east of northern Japan.

This cloud pattern is a common sight over the northwestern Pacific. Classified as low-level clouds - occurring below 6,500 feet (1,980 meters) - stratocumulus clouds produce little to no precipitation. From the ground they look like a flat layer of clumpy grey clouds. (See more pictures of clouds.)

2. Crowning Glory

It's official: barred spiral galaxy NGC 6872 is king of the (galactic) hill. An international team of astronomers has confirmed that NGC 6872 (pictured), long thought to be one of the largest stellar systems in the universe, is indeed the biggest known spiral galaxy.

Located in the southern constellation Pavo, 212 million light-years from Earth, this newly crowned behemoth stretches 522,000 light-years from one end to the other.

The galaxy's portrait, released January 10, is a composite of visible light, ultraviolet, and infrared radiation detected by the European Southern Observatory's Very Large Telescope and NASA's Spitzer Space Telescope and GALEX. (See more pictures of galaxies.)

3. Pre-flight Check

Boeing technicians, swathed in clean-room suits, check the first of NASA's next generation satellites being deployed to act as relays between scientific instruments orbiting Earth and controllers on the ground, in an image released January 11. (Learn about satellites and space junk.)

NASA's Tracking and Data Relay Satellite-K (TDRS-K) will join a fleet of seven geostationary satellites already in orbit when it launches from Cape Canaveral in Florida on January 29. These satellites provide telemetry, tracking, command, and high-bandwidth data return services for scientific missions and instruments, including the International Space Station and the Hubble Space Telescope, circling the globe.

Technicians will pack the TDRS-K - outfitted with new solar panels to provide more power than previous satellites in NASA's space fleet - into a vehicle nose cone to protect it during its flight aboard an Atlas V rocket. (Learn about expendable launch vehicles.)

4. Rock Art at Night

This image of Native American petroglyphs, or rock art, shot against the Milky Way, was taken in California's eastern Sierra Nevada on January 14.

Petroglyphs - one of many forms of rock art - are created by scraping, rubbing, or chiselling designs into the patina coating desert rocks. Depending on the conditions surrounding a piece of rock art, these designs can endure for hundreds to thousands of years. (Watch a video about Arizona's rock art.)

Erosion and natural processes, such as plant growth, can fade or destroy the designs. They can also fall victim to vandalism and theft.

According to news reports, one of the most recent incidences was discovered in late October 2012. Unknown perpetrators hacked six petroglyphs out of the cliff face at the Eastern Sierra Volcanic Tableland near Bishop, California (map). They damaged others using saws and hammers.

5. Hazy Days

Beijing hit a dubious milestone on January 12, when the U.S. embassy located in the Chinese city recorded an Air Quality Index - a scale used by the U.S. Environmental Protection Agency to measure air pollution - of 755. According to news reports, this was the highest level recorded since the embassy began tracking air pollution in 2008.

Readings above 500 are considered by the World Health Organization to be 20 times the level of particulate matter deemed safe for humans.

In this satellite image, taken January 14, grey-brown streaks of pollution hover over Beijing (centre), and mar the bright white spots indicating snowfall.

6. Solar Eruptions

The sun kicked off the new year by throwing a tantrum of sorts, blasting six eruptive prominences - huge loops of plasma that can escape and give rise to coronal mass ejections - from its surface.

This image, taken by a pair of satellites collectively called STEREO and released January 14, captured the roiling solar activity in extreme UV light.

The sun experiences cycles of activity that last for around 11 years. The most recent quiet period, with a drop in the number of sun spots and diminished solar flare activity, lasted three years beginning in 2008. But things started to pick up again in 2011, and astronomers believe the sun is heading into a period of maximum activity in 2013.

[Source: National Geographic News. Edited.]