Chad Allison

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APOD: A Year on the Sun (2013 Apr 26) Image Credit: NASA, Solar Dynamics Observatory http://apod.nasa.gov/apod/ap130426.html Explanation: Our solar system's miasma of incandescent plasma, the Sun may look a little scary here. The picture is a composite of 25 images recorded in extreme ultraviolet light by the orbiting Solar Dynamics Observatory between April 16, 2012 and April 15, 2013. The particular wavelength of light, 171 angstroms, shows emission from highly ionized iron atoms in the solar corona at a characteristic temperatures of about 600,000 kelvins (about 1 million degrees F). Girdling both sides of the equator during the approach to maximum in its 11-year solar cycle, the solar active regions are laced with bright loops and arcs along magnetic field lines. Of course, a more familiar visible light view would show the bright active regions as groups of dark sunspots. Three years of Solar Dynamics Observatory images are compressed into this short video. http://www.nasa.gov/mission_pages/sdo/news/first-light-3rd.html http://www.youtube.com/watch?v=dHvPJp9YFfY Starship Asterisk* • APOD Discussion Page http://asterisk.apod.com/discuss_apod.php?date=130426 Starship Asterisk* • On This Day in APOD http://asterisk.apod.com/view_retro.php?date=0426

APOD: Earth's Richat Structure (2013 May 19) Image Credit: NASA/GSFC/METI/Japan Space Systems, and U.S./Japan ASTER Science Team http://apod.nasa.gov/apod/ap130519.html Explanation: What on Earth is that? The Richat Structure in the Sahara Desert of Mauritania is easily visible from space because it is nearly 50 kilometers across. Once thought to be an impact crater, the Richat Structure's flat middle and lack of shock-altered rock indicates otherwise. The possibility that the Richat Structure was formed by a volcanic eruption also seems improbable because of the lack of a dome of igneous or volcanic rock. Rather, the layered sedimentary rock of the Richat structure is now thought by many to have been caused by uplifted rock sculpted by erosion. The above image was captured by the ASTER instruments onboard the orbiting orbiting Terra satellite. Why the Richat Structure is nearly circular remains a mystery. http://asterweb.jpl.nasa.gov/gallery-detail.asp?name=Richat Starship Asterisk* • APOD Discussion Page http://asterisk.apod.com/discuss_apod.php?date=130519 Starship Asterisk* • On This Day in APOD http://asterisk.apod.com/view_retro.php?date=0519

APOD: Caterpillar Moon (2013 May 24) Image Credit & Copyright: Joerg Kopplin http://apod.nasa.gov/apod/ap130524.html Explanation: A close series of consecutive exposures are combined in this intriguing composite of the Full Moon slowly crawling, across the sky. Beginning on the upper right at 19:42 UT and ending at 22:14 UT on April 25, the sequence follows the Moon from Germany as it passes through Earth's shadow in a partial lunar eclipse. Near the top, the Moon just grazes the southern edge of Earth's dark central shadow, or umbra. But the decreased brightness in the darker part of the outer shadow region, the penumbra, is also apparent on the lunar disk. In fact, the relative size and shape of the Earth's shadow regions and the Moon are easier to see along the segments of this lunar caterpillar. Nearly impossible to follow with the eye though, a penumbral lunar eclipse, the Full Moon passing only through the pale outer penumbral shadow, will begin on May 25. Starship Asterisk* • APOD Discussion Page http://asterisk.apod.com/discuss_apod.php?date=130524 Starship Asterisk* • On This Day in APOD http://asterisk.apod.com/view_retro.php?date=0524

APOD: Lunar Corona over Cochem Castle (2013 May 25) Image Credit & Copyright: Babak Tafreshi (TWAN) http://apod.nasa.gov/apod/ap130525.html Explanation: This bat-like apparition does not shine on clouds passing over Gotham city. Instead, the cloud bank in silhouette against a colorful lunar corona was spotted on the evening of May 18 over Cochem, Germany from the banks of the river Mossele. The lunar corona is formed as bright moonlight is diffracted by water droplets in thin clouds drifting in front of the lunar disk. Below it lies the region's historic Cochem Castle dating from the 11th century, and not Wayne Manor. Still, regardless of your location on planet Earth it is well worth scanning the evening skies this weekend, as a Full Moon rises and bright planets gather in the west. http://twanight.org/tafreshi http://dreamview.net/ Starship Asterisk* • APOD Discussion Page http://asterisk.apod.com/discuss_apod.php?date=130525 Starship Asterisk* • On This Day in APOD http://asterisk.apod.com/view_retro.php?date=0525

APOD: PanSTARRS Anti-Tail Grows (2013 May 26) Image Credit & Copyright: Joseph Brimacombe http://apod.nasa.gov/apod/ap130526.html Explanation: As planet Earth approached the plane of the Comet PanSTARRS (C/2011 L4) orbit on May 23rd, comet watchers were treated to this view of its magnificent anti-tail. The long, narrow anti-tail stretches to the right across this frame for nearly 4 degrees or about 8 times the angular size of the full Moon. The tail trails along the comet's orbit as it leaves the inner solar system behind. An almost edge-on perspective from near the outbound comet's orbital plane enhances the view of the anti-tail and makes it seem to point in the sunward direction, only apparently contrary to the behavior of comet dust tails pushed outward by the pressure of sunlight. Sweeping far north in planet Earth's skies, the comet is up all night for most of the northern hemisphere, but now bright moonlight interferes with its visibility. PanSTARRS anti-tail is one of the longest since the appearance of Comet Arend-Roland in 1957. http://www.flickr.com/photos/43846774@N02/ Starship Asterisk* • APOD Discussion Page http://asterisk.apod.com/discuss_apod.php?date=130526 Starship Asterisk* • On This Day in APOD http://asterisk.apod.com/view_retro.php?date=0526

APOD: Bird Sun Dog (2013 May 27) Image Credit & Copyright: Juan Manuel Pérez Rayego http://apod.nasa.gov/apod/ap130527.html Explanation: Have you ever seen a little rainbow off to the side of the Sun? Rare but rewarding to see, such spectacles are known as sundogs, mock suns or parhelia. Sundogs are just sunlight refracting through hexagonal falling ice crystals in the Earth's atmosphere. When thin ice crystals flitter down nearly horizontally, they best refract sunlight sideways and create sundogs. Alternatively, randomly oriented ice crystals may create a complete circular sun halo. Sundogs occur 22 degrees to each side of a setting or rising Sun, although sometimes nearby clouds can block one or both. The above image was taken through a polarizing filter during October 2012 in Mérida, Spain. Starship Asterisk* • APOD Discussion Page http://asterisk.apod.com/discuss_apod.php?date=130527 Starship Asterisk* • On This Day in APOD http://asterisk.apod.com/view_retro.php?date=0527