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Astronomy Picture of the Day


Phobos 360

What does the Martian moon Phobos look like? To better visualize this unusual object, images from ESA’s Mars Express orbiter have been combined into a virtual rotation movie. The rotation is actually a digital illusion — tidally-locked Phobos always keeps the same face toward its home planet, as does Earth’s moon. The above video highlights Phobos’ chunky shape and an unusually dark surface covered with craters and grooves. What lies beneath the surface is a topic of research since the moon is not dense enough to be filled with solid rock. Phobos is losing about of centimeter of altitude a year and is expected to break up and crash onto Mars within the next 50 million years. To better understand this unusual world, Mars Express is on course to make the closest flyby ever on Sunday.

Video Credit: Mars Express, ESA

Sharpless 308: Star Bubble

Blown by fast winds from a hot, massive star, this cosmic bubble is huge. Cataloged as Sharpless 2-308 it lies some 5,200 light-years away toward the constellation of the Big Dog (Canis Major) and covers slightly more of the sky than a Full Moon. That corresponds to a diameter of 60 light-years at its estimated distance. The massive star that created the bubble, a Wolf-Rayet star, is the bright one near the center of the nebula. Wolf-Rayet stars have over 20 times the mass of the Sun and are thought to be in a brief, pre-supernova phase of massive star evolution. Fast winds from this Wolf-Rayet star create the bubble-shaped nebula as they sweep up slower moving material from an earlier phase of evolution. The windblown nebula has an age of about 70,000 years. Relatively faint emission captured in the expansive image is dominated by the glow of ionized oxygen atoms mapped to violet hues.

Image Credit & Copyright: Jeff Husted

Geminid Meteors over Chile

From a radiant point in the constellation of the Twins, the annual Geminid meteor shower rained down on planet Earth over the past few weeks. Recorded near the shower’s peak over the night of December 13 and 14, the above skyscape captures Gemini’s shooting stars in a four-hour composite from the dark skies of the Las Campanas Observatory in Chile. In the foreground the 2.5-meter du Pont Telescope is visible as well as the 1-meter SWOPE telescope. The skies beyond the meteors are highlighted by Jupiter, seen as the bright spot near the image center, the central band of our Milky Way Galaxy, seen vertically on the image left, and the pinkish Orion Nebula on the far left. Dust swept up from the orbit of active asteroid 3200 Phaethon, Gemini’s meteors enter the atmosphere traveling at about 22 kilometers per second.

Image Credit & Copyright: Yuri Beletsky (Las Campanas Observatory, Carnegie Institution)

Tutulemma: Solar Eclipse Analemma

If you went outside at exactly the same time every day and took a picture that included the Sun, how would the Sun’s position change? With great planning and effort, such a series of images can be taken. The figure-8 path the Sun follows over the course of a year is called an analemma. Yesterday, the Winter Solstice day in Earth’s northern hemisphere, the Sun appeared at the bottom of the analemma. Analemmas created from different latitudes would appear at least slightly different, as well as analemmas created at a different time each day. With even greater planning and effort, the series can include a total eclipse of the Sun as one of the images. Pictured is such a total solar eclipse analemma or Tutulemma - a term coined by the photographers based on the Turkish word for eclipse. The above composite image sequence was recorded from Turkey starting in 2005. The base image for the sequence is from the total phase of a solar eclipse as viewed from Side, Turkey on 2006 March 29. Venus was also visible during totality, toward the lower right.

Image Credit & Copyright: Cenk E. Tezel and Tunç Tezel (TWAN)

SDO’s Multiwavelength Sun

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.

Image Credit: GSFC Scientific Visualization Studio, SDO, NASA

Titan’s Land of Lakes

Saturn’s large moon Titan would be unique in our solar system, the only world with stable liquid lakes and seas on its surface … except for planet Earth of course. Centered on the north pole, this colorized map shows Titan’s bodies of methane and ethane in blue and black, still liquid at frigid surface temperatures of -180 degrees C (-292 degrees F). The map is based on data from the Cassini spacecraft’s radar, taken during flybys between 2004 and 2013. Roughly heart-shaped, the lake above and right of the pole is Ligeia Mare, the second largest known body of liquid on Titan and larger than Lake Superior on Earth. Just below the north pole is Punga Mare. The sprawling sea below and right of Punga is the (hopefully sleeping) Kraken Mare, Titan’s largest known sea. Above and left of the pole, the moon’s surface is dotted with smaller lakes that range up to 50 kilometers across.

Image Credit: Cassini Radar Mapper, JPL, USGS, ESA, NASA

A Colorful Moon

The Moon is normally seen in subtle shades of grey or yellow. But small, measurable color differences have been greatly exaggerated to make this telescopic, multicolored, moonscape captured during the Moon’s full phase. The different colors are recognized to correspond to real differences in the chemical makeup of the lunar surface. Blue hues reveal titanium rich areas while orange and purple colors show regions relatively poor in titanium and iron. The familiar Sea of Tranquility, or Mare Tranquillitatis, is the blue area in the upper right corner of the frame. White lines radiate across the orange-hued southern lunar highlands from 85 kilometer wide ray crater Tycho at bottom left. Above it, darker rays from crater Copernicus extend into the Sea of Rains (Mare Imbrium) at the upper left. Calibrated by rock samples from the Apollo missions, similar multicolor images from spacecraft have been used to explore the Moon’s global surface composition.

Image Credit & Copyright: László Francsics

Light Pillars over Finland

What’s happening behind those houses? Pictured above are not aurora but nearby light pillars, a local phenomenon that can appear as a distant one. In most places on Earth, a lucky viewer can see a Sun-pillar, a column of light appearing to extend up from the Sun caused by flat fluttering ice-crystals reflecting sunlight from the upper atmosphere. Usually these ice crystals evaporate before reaching the ground. During freezing temperatures, however, flat fluttering ice crystals may form near the ground in a form of light snow, sometimes known as a crystal fog. These ice crystals may then reflect ground lights in columns not unlike a Sun-pillar. While going out to buy cat food, a quick thinking photographer captured the above light pillars extending up from bright parking lot lights in Oulu, Finland.

Image Credit & Copyright: Thomas Kast

Geminid Meteors over Teide Volcano

On some nights it rains meteors. Peaking two nights ago, asteroid dust streaked through the dark skies of Earth, showering down during the annual Geminids meteor shower. Astrophotographer Juan Carlos Casado captured the space weather event, as pictured above, in a series of exposures spanning about 2.3 hours using a wide angle lens. The snowcapped Teide volcano of the Canary Islands of Spain towers in the foreground, while the picturesque constellation of Orion highlights the background. The star appearing just near the top of the volcano is Rigel. Although the asteroid dust particles are traveling parallel to each other, the resulting meteor streaks appear to radiate from a single point on the sky, in this case in the constellation of Gemini, off the top of the image. Like train tracks appearing to converge in the distance, the meteor radiant effect is due to perspective. The astrophotographer has estimated that there are about 50 Geminids visible in the above composite image — how many do you see?

Image Credit & Copyright: Juan Carlos Casado (TWAN, Earth and Stars)

Yutu Rover Rolls onto the Moon

A new desk-sized rover has begun exploring the Moon. Launched two weeks ago by the Chinese National Space Administration, the Chang’e 3 spacecraft landed on the Moon yesterday and deployed the robotic rover. Yutu, named for a folklore lunar Jade Rabbit, has a scheduled three-month mission to explore several kilometers inside the Sinus Iridum (Latin for “Bay of Rainbows”) impact crater. Yutu’s cameras and spectrometers will investigate surface features and composition while ground penetrating radar will investigate deep soil structure. Chang’e 3 achieved the first soft Moon landing since the Soviet Union’s Luna 24 in 1976, and Yutu is the first lunar rover deployed since the USSR’s Lunokhod 2 in 1973. Pictured above, Yutu was imaged from its lander yesterday soon after rolling onto the Moon.

Image Credit: Chinese National Space Administration, Xinhuanet

Gibbous Europa

Although the phase of this moon might appear familiar, the moon itself might not. In fact, this gibbous phase shows part of Jupiter’s moon Europa. The robot spacecraft Galileo captured this image mosaic during its mission orbiting Jupiter from 1995 - 2003. Visible are plains of bright ice, cracks that run to the horizon, and dark patches that likely contain both ice and dirt. Raised terrain is particularly apparent near the terminator, where it casts shadows. Europa is nearly the same size as Earth’s Moon, but much smoother, showing few highlands or large impact craters. Evidence and images from the Galileo spacecraft, indicated that liquid oceans might exist below the icy surface. To test speculation that these seas hold life, ESA has started preliminary development of the Jupiter Icy Moons Explorer (JUICE), a spacecraft proposed for launch around 2022 that would further explore Jupiter and in particular Europa. Recent observations by the Hubble Space Telescope have uncovered new evidence that Europa, like Saturn’s moon Enceladus, has ice venting from its surface.

Image Credit: Galileo Project, JPL, NASA; Copyright, Reprocessed By: Ted Stryk

The Bubble Nebula

Blown by the wind from a massive star, this interstellar apparition has a surprisingly familiar shape. Cataloged as NGC 7635, it is also known simply as The Bubble Nebula. Although it looks delicate, the 10 light-year diameter bubble offers evidence of violent processes at work. Above and right of the Bubble’s center is a hot, O star, several hundred thousand times more luminous and around 45 times more massive than the Sun. A fierce stellar wind and intense radiation from that star has blasted out the structure of glowing gas against denser material in a surrounding molecular cloud. The intriguing Bubble Nebula lies a mere 11,000 light-years away toward the boastful constellation Cassiopeia. This natural looking view of the cosmic bubble is composed from narrowband image data, also used to create a 3D model.

Image Credit & Copyright: J-P Metsävainio (Astro Anarchy)

Geminid Meteor Shower over Dashanbao Wetlands

The annual Geminid meteor shower is raining down on planet Earth this week. Despite the waxing gibbous moonlight, the reliable Geminids should be enjoyable tonight (night of December 13/14) near the shower’s peak. Recorded near last year’s peak in the early hours of December 14, 2012, this skyscape captures many of Gemini’s lovely shooting stars. The careful composite of exposures was made during a three hour period overlooking the Dashanbao Wetlands in central China. Dark skies above are shared with bright Jupiter (right), Orion, (right of center) and the faint band of the Milky Way. The shower’s radiant in the constellation Gemini, the apparent source of all the meteor streaks, lies just above the top of the frame. Dust swept up from the orbit of active asteroid 3200 Phaethon, Gemini’s meteors enter the atmosphere traveling at about 22 kilometers per second.

Image Credit & Copyright: Jeff Dai

Alnitak, Alnilam, Mintaka

Alnitak, Alnilam, and Mintaka, are the bright bluish stars from east to west (lower right to upper left) along the diagonal in this gorgeous cosmic vista. Otherwise known as the Belt of Orion, these three blue supergiant stars are hotter and much more massive than the Sun. They lie about 1,500 light-years away, born of Orion’s well-studied interstellar clouds. In fact, clouds of gas and dust adrift in this region have intriguing and some surprisingly familiar shapes, including the dark Horsehead Nebula and Flame Nebula near Alnitak at the lower right. The famous Orion Nebula itself is off the right edge of this colorful star field. The well-framed, wide-field telescopic image spans about 4 degrees on the sky.

Image Credit & Copyright: Rogelio Bernal Andreo (Deep Sky Colors)

The Coldest Place on Earth

How cold can it get on Earth? In the interior of the Antarctica, a record low temperature of -93.2 °C (-135.8 °F) has been recorded. This is about 25 °C (45 °F) colder than the coldest lows noted for any place humans live permanently. The record temperature occurred in 2010 August — winter in Antarctica — and was found by scientists sifting through decades of climate data taken by Earth-orbiting satellites. The coldest spots were found near peaks because higher air is generally colder, although specifically in depressions near these peaks because relatively dense cold air settled there and was further cooled by the frozen ground. Summer is a much better time to visit Antarctica, as some regions will warm up as high as 15 °C (59 °F).

Image Credit: Ted Scambos (National Snow and Ice Data Center) et al., Landsat 8, USGS, NASA