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February 27th, 2015

Moon inside Winter Hexagon on February 27th

Tonight’s waxing gibbous moon is inside or near a large asterism that is called the Winter Circle.

Image from Star Walk 2

Image from Star Walk 2

The Winter Hexagon or Winter Circle/Oval is an asterism appearing to be in the form of a hexagon with vertices at Rigel, Aldebaran, Capella, Pollux, Procyon, and Sirius. It is mostly upon the Northern Hemisphere’s celestial sphere. On most locations on Earth (except the South Island of New Zealand and the south of Chile and Argentina and further south), this asterism is prominently in the sky from approximately December to March. In the tropics and southern hemisphere, this (then called “summer hexagon”) can be extended with the bright star Canopus in the south.

The Winter Circle in blue and the Winter Triangle in red. Image via Wikimedia Commons


February 24th, 2015

Swirling Vortex on Venus

Image: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA/Univ. Oxford

This ghostly puff of smoke is actually a mass of swirling gas and cloud at Venus’ south pole, as seen by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) aboard ESA’s Venus Express spacecraft.

Venus has a very choppy and fast-moving atmosphere – although wind speeds are sluggish at the surface, they reach dizzying speeds of around 400 km/h at the altitude of the cloud tops, some 70 km above the surface. At this altitude, Venus’ atmosphere spins round some 60 times faster than the planet itself. This is very rapid; even Earth’s fastest winds move at most about 30% of our planet’s rotation speed. Quick-moving Venusian winds can complete a full lap of the planet in just four Earth days.

Polar vortices form because heated air from equatorial latitudes rises and spirals towards the poles, carried by the fast winds. As the air converges on the pole and then sinks, it creates a vortex much like that found above the plughole of a bath. In 1979, the Pioneer Venus orbiter spotted a huge hourglass-shaped depression in the clouds, some 2000 km across, at the centre of the north polar vortex. However, other than brief glimpses from the Pioneer Venus and Mariner 10 missions in the 1970s, Venus’ south pole had not been seen in detail until ESA’s Venus Express first entered orbit in April 2006.

One of Venus Express’ first discoveries, made during its very first orbit, was confirming the existence of a huge atmospheric vortex circulation at the south pole with a shape matching the one glimpsed at the north pole.

This south polar vortex is a turbulent mix of warming and cooling gases, all surrounded by a ‘collar’ of cool air. Follow-up Venus Express observations in 2007, including this image, showed that the core of the vortex changes shape on a daily basis. Just four hours after this image the vortex looked very different and a day later it had morphed into a squashed shape unrecognisable from the eye-like structure here.

A video of the vortex, made from 10 images taken over a period of five hours, can be seen here. The vortex rotates with a period of around 44 hours.

The swirling region shown in this VIRTIS image is about 60 km above the planet’s surface. Venus’ south pole is located just up and to the left of the image centre, slightly above the wispy ‘eye’ itself.

This image was obtained on 7 April 2007 at a wavelength of 5.02 micrometres. It shows thermal-infrared emission from the cloud tops; brighter regions like the ‘eye’ of the vortex are at lower altitude and therefore hotter.

Original post: ESA

 

 


February 19th, 2015

New Year, New Moon

Photograph taken by ESA astronaut Luca Parmitano from on board the International Space Station showing a rising crescent Moon seen through rare noctilucent clouds.

The Chinese New Year for 2015 is celebrated on February 18-19. It’s the most important of Chinese holidays, celebrated by billions of people across the world. Festivities traditionally last for 15 days to culminate with the Lantern Festival. This calendar is based on a complex lunisolar calendar system that uses both lunar and solar cycles to mark time. As a result, Chinese New Year falls on different dates each year, between January 21 and February 21 of the conventional Gregorian calendar. Each Chinese lunar year is associated with one of twelve animals in the Chinese zodiac. For 2015, it’s the Year of the Sheep (Goat).

Chinese New Year celebrations traditionally lasts 15 days, from the first day (during a new moon) to the 15th day (the next full moon). Each day holds a special significance that varies according to local traditions. But first, before the arrival of the new year, homes are thoroughly cleaned to sweep away ill fortune, and to welcome good luck. On new year’s eve, there are family gatherings to celebrate and enjoy sumptuous traditional feasts, and to greet the new year with fireworks at midnight.

Happy Chinese New Year 2015!

Image credit:  ESA/NASA

Original post: EarthSky


February 18th, 2015

Cappuccino Swirls at Mars’ South Pole

 

Swirls of chocolate, caramel and cream – this image is definitely one to trigger sweet-toothed cravings. Smooth cream-coloured plateaus surrounded by cocoa-dusted ridges interspersed with caramel-hued streaks create a scene reminiscent of a cosmic cappuccino.

This picture is, perhaps surprisingly, from ESA’s Mars Express, which has been exploring and imaging the martian surface and atmosphere since 2003. We may be used to seeing numerous images of red and brown-hued soil and ruddy landscapes peppered with craters, but the Red Planet isn’t always so red.

The bright white region of this image shows the icy cap that covers Mars’ south pole, composed of frozen water and carbon dioxide. While it looks smooth in this image, at close quarters the cap is a layered mix of peaks, troughs and flat plains, and has been likened in appearance to swiss cheese.

The southern cap reaches some 3 km thick in places, and is around 350 km in diameter. This icy region is permanent; in the martian winter another, thinner ice cap forms over the top of it, stretching further out across the planet and disappearing again when the weather warms up.

The cap is around 150 km north of Mars’ geographical south pole and Mars Express has shed light on why this ice cap is displaced. Deep impact craters – notably the Hellas Basin, the largest impact structure on the entire planet at 7 km deep and 2300 km across – funnel the strong winds that blow across Mars towards its southern pole, creating a mix of different low- and high-pressure systems. The carbon dioxide in the polar cap sublimates at different rates in these regions with contrasting pressure, resulting in the cap’s lopsided structure.

Mars Express imaged this area of Mars on 17 December 2012, in infrared, green and blue light, using its High Resolution Stereo Camera. This image was processed by Bill Dunford, using data available from the ESA Planetary Science Archive.

Credit: ESA/DLR/FU Berlin / Bill Dunford


February 16th, 2015

Neptune False Color Image of Haze

Image credit: NASA/JPL

This false color photograph of Neptune was made from Voyager 2 images taken through three filters: blue, green, and a filter that passes light at a wavelength that is absorbed by methane gas. Thus, regions that appear white or bright red are those that reflect sunlight before it passes through a large quantity of methane. The image reveals the presence of a ubiquitous haze that covers Neptune in a semitransparent layer. Near the center of the disk, sunlight passes through the haze and deeper into the atmosphere, where some wavelengths are absorbed by methane gas, causing the center of the image to appear less red. Near the edge of the planet, the haze scatters sunlight at higher altitude, above most of the methane, causing the bright red edge around the planet. By measuring haze brightness at several wavelengths, scientists are able to estimate the thickness of the haze and its ability to scatter sunlight. The image is among the last full disk photos that Voyager 2 took before beginning its endless journey into interstellar space. The Voyager Mission is conducted by JPL for NASA’s Office of Space Science and Applications.

Credit: NASA/JPL