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Astronomy Picture of the Day

Anticrepuscular Rays Converge Opposite the Sun
Image Credit & Copyright: Juraj Patekar

Explanation: Is there ever anything interesting to see in the direction opposite the Sun? Sometimes there is. Notable items include your own shadow, a shadow of the Moon during a total solar eclipse, a full moonin eclipse if the alignment’s good enough, a full earth, planets at opposition, glints from planets, the gegenschein from interplanetary dust, the center of a rainbow, hall-of-mountain fogbows, an airplane glory, and something yet again different if your timing, clouds and Sun position are just right. This different effect starts with clouds near the Sun that are causing common crepuscular rays to stream though. In the featured rare image taken from an airplane in mid-April, these beams were caught converging 180 degrees around, on the opposite side of the sky from the Sun, where they are called anticrepuscular rays. Therefore, it may look like something bright is shining at the antisolar point near the image center, but actually it is reverse-shining because, from your direction, light is streaming in, not out.

Tomorrow’s picture: star bright

Astronomy Picture of the Day

Carina Nebula Panorama from Hubble
Image Credit: NASA, ESA, N. Smith (U. California, Berkeley) et al., and The Hubble Heritage Team (STScI/AURA)

Explanation: How do violent stars affect their surroundings? To help find out, astronomers created a 48-frame high-resolution, controlled-color panorama of the center of the Carina Nebula, one of the largest star forming regions on the night sky. The featured image, taken in 2007, was the most detailed image of the Carina Nebula yet taken. Cataloged as NGC 3372, the Carina Nebula is home to streams of hot gas, pools of cool gas, knots of dark globules, and pillars of dense dusty interstellar matter. The Keyhole Nebula, visible left of center, houses several of the most massive stars known. These large and violent stars likely formed in dark globules and continually reshape the nebula with their energetic light, outflowing stellar winds, and ultimately by ending their lives in supernova explosions. Visible to the unaided eye, the entire Carina Nebula spans over 450 light years and lies about 8,500 light-years away toward the constellation of Ship’s Keel (Carina).

Tomorrow’s picture: look back

Astronomy Picture of the Day

Ares 3 Landing Site: The Martian Revisited
Image Credit: HiRISE, MRO, LPL (U. Arizona), NASA

Explanation: This close-up from the Mars Reconnaissance Orbiter’s HiRISE camera shows weathered craters and windblown deposits in southern Acidalia Planitia. A striking shade of blue in standard HiRISE image colors, to the human eye the area would probably look grey or a little reddish. But human eyes have not gazed across this terrain, unless you count the eyes of NASA astronauts in the scifi novel The Martian by Andy Weir. The novel chronicles the adventures of Mark Watney, an astronaut stranded at the fictional Mars mission Ares 3 landing site corresponding to the coordinates of this cropped HiRISE frame. For scale Watney’s 6-meter-diameter habitat at the site would be about 1/10th the diameter of the large crater. Of course, the Ares 3 landing coordinates are only about 800 kilometers north of the (real life) Carl Sagan Memorial Station, the 1997 Pathfinder landing site.

Tomorrow’s picture: panorama carina

Astronomy Picture of the Day

Sunset Analemma
Image Credit & Copyright: Marcella Giulia Pace

Explanation: Today, the solstice is at 15:54 Universal Time, the Sun reaching the northernmost declination in its yearly journey through planet Earth’s sky. A June solstice marks the astronomical beginning of summer in the northern hemisphere and winter in the south. It also brings the north’s longest day, the longest period between sunrise and sunset. In fact the June solstice sun is near the top, at the most northern point in the analemma or figure 8 curve traced by the position of the Sun in this composite photo. The analemma was created (video) from images taken every 10 days at the same time from June 21, 2018 and June 7, 2019. The time was chosen to be the year’s earliest sunset near the December solstice, so the analemma’s lowest point just kisses the unobstructed sea horizon at the left. Sunsets arranged along the horizon toward the right (north) are centered on the sunset at the September equinox and end with sunset at the June solstice.

Tomorrow’s picture: pixels revisited

Astronomy Picture of the Day

A View Toward M106
Image Credit: Phil Keyser

Explanation: Big, bright, beautiful spiral, Messier 106 dominates this cosmic vista. The nearly two degree wide telescopic field of view looks toward the well-trained constellation Canes Venatici, near the handle of the Big Dipper. Also known as NGC 4258, M106 is about 80,000 light-years across and 23.5 million light-years away, the largest member of the Canes II galaxy group. For a far away galaxy, the distance to M106 is well-known in part because it can be directly measured by tracking this galaxy’s remarkable maser, or microwave laser emission. Very rare but naturally occurring, the maser emission is produced by water molecules in molecular clouds orbiting its active galactic nucleus. Another prominent spiral galaxy on the scene, viewed nearly edge-on, is NGC 4217 below and right of M106. The distance to NGC 4217 is much less well-known, estimated to be about 60 million light-years.

Tomorrow’s picture: analemma at sunset

Astronomy Picture of the Day

Our Galaxy’s Magnetic Center
Image Credit: NASA, SOFIA, Hubble

Explanation: What’s the magnetic field like in the center of our Milky Way Galaxy? To help find out, NASA’s SOFIA — an observatory flying in a modified 747 — imaged the central region with an instrument known as HAWC+. HAWC+ maps magnetism by observing polarized infrared light emitted by elongated dust grains rotating in alignment with the local magnetic field. Now at our Milky Way’s center is a supermassive black hole with a hobby of absorbing gas from stars it has recently destroyed. Our galaxy’s black hole, though, is relatively quiet compared to the absorption rate of the central black holes in active galaxies. The featured image gives a clue as to why — a surrounding magnetic field may either channel gas into the black hole — which lights up its exterior, or forces gas into an accretion-disk holding pattern, causing it to be less active — at least temporarily. Inspection of the featured image — appearing perhaps like a surreal mashup of impasto art and gravitational astrophysics — brings out this telling clue by detailing the magnetic field in and around a dusty ring surrounding Sagittarius A*, the black hole in our Milky Way’s center.

Tomorrow’s picture: maser spiral

Astronomy Picture of the Day

Strawberry Moon over the Temple of Poseidon
Image Credit & Copyright: Elias Chasiotis

Explanation: Did you see the full moon last night? If not, tonight’s nearly full moon should be almost as good. Because full moons are opposite the Sun, they are visible in the sky when the Sun is not — which should be nearly all night long tonight, clouds permitting. One nickname for June’s full moon is the Strawberry Moon, named for when wild strawberries start to ripen in parts of Earth‘s northern hemisphere. Different cultures around the globe give this full moon different names, though, including Honey Moon and Rose Moon. In the foreground of this featured image, taken yesterday in Cape Sounion, Greece, is the 2,400 year-old Temple of Poseidon. Next month will the 50th anniversary of the time humans first landed on the Moon.

Tomorrow’s picture: black hole magnetism