APOD Retrospective: August 12

A nostalgic look back at Astronomy Picture of the Day
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APOD Retrospective: August 12

Post by bystander » Fri Aug 12, 2011 4:53 am

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2015 Tonight the Perseid Meteor Shower reaches its maximum. Grains of icy rock will streak across the sky as they evaporate during entry into Earth's atmosphere. These grains were shed from Comet Swift-Tuttle. The Perseids result from the annual crossing of the Earth through Comet Swift-Tuttle's orbit, and are typically the most active meteor shower of the year. Although it is hard to predict the level of activity in any meteor shower, in a clear dark sky an observer might see a meteor a minute. This year's Perseids occur just before a new Moon and so the relatively dark sky should make even faint meteors visible. Meteor showers in general are best be seen from a relaxing position, away from lights. Featured here is a meteor caught exploding two weeks ago above Austria next to the central band of our Milky Way Galaxy.





2010 Each August, as planet Earth swings through dust trailing along the orbit of periodic comet Swift-Tuttle, skygazers can enjoy the Perseid Meteor Shower. The shower should build to its peak now, best seen from later tonight after moonset, until dawn tomorrow morning when Earth moves through the denser part of the wide dust trail. But shower meteors have been spotted for many days, like this bright Perseid streaking through skies near Lake Balaton, Hungary on August 8. In the foreground is the region's Church of St. Andrew ruin, with bright Jupiter dominating the sky to its right. Two galaxies lie in the background of the wide-angle, 3 frame panorama; our own Milky Way's luminous arc, and the faint smudge of the more distant Andromeda Galaxy just above the ruin's leftmost wall. If you watch for Perseid meteors tonight, be sure and check out the early evening sky show too, featuring bright planets and a young crescent Moon near the western horizon after sunset.



2007 Tonight is a good night to see meteors. Comet dust will rain down on planet Earth, streaking through dark skies in the annual Perseid meteor shower. While enjoying the anticipated space weather, astronomer Fred Bruenjes recorded a series of many 30 second long exposures spanning about six hours on the night of 2004 August 11/12 using a wide angle lens. Combining those frames which captured meteor flashes, he produced this dramatic view of the Perseids of summer. Although the comet dust particles are traveling parallel to each other, the resulting shower meteors clearly seem to radiate from a single point on the sky in the eponymous constellation Perseus. The radiant effect is due to perspective, as the parallel tracks appear to converge at a distance. Bruenjes notes that there are 51 Perseid meteors in the composite image, including one seen nearly head-on. This year, the Perseids Meteor Shower is expected to peak after midnight tonight, in the moonless early morning hours of August 12.



2004 Chasing the brief flash of a meteor trail across the sky with a very large telescope is a nearly impossible task. But on May 12, 2002, astronomers got lucky, as a bright meteor chanced across the narrow slit of their spectrograph at the Paranal Observatory. At the time, the spectrograph was being used to study the light from a supernova, separating and recording the many near-infrared emission lines produced by atoms in the distant stellar explosion. Below this artistic montage of a meteor streak and Very Large Telescope units at Paranal, panel a shows the near-infrared sky background spectrum and the May 12 meteor combined. Panel b shows the emission spectrum of the meteor alone, after subtracting away the background contributions. The meteor emission is due to colliding oxygen and nitrogen atoms and molecules in the superheated air along the glowing trail at an altitude of about 100 kilometers.

2003 Stephan's Quintet is a picturesque but clearly troubled grouping of galaxies about 300 million light-years away toward the high-flying constellation Pegasus. Spanning over 200,000 light-years at that distance, this composite false-color image illustrates the powerful nature of this multiple galaxy collision, showing x-ray data from the Chandra Observatory in blue superposed on optical data in yellow. The x-rays from the central blue cloud running vertically through the image are produced by gas heated to millions of degrees by an energetic shock on a cosmic scale. The shock was likely the result of the interstellar gas in the large spiral galaxy, seen immediately to the right of the cloud, colliding with the quintet's tenuous intergalactic gas as this galaxy plunged through group's central regions. In fact, over billions of years, repeated passages of the group galaxies through the hot intergalactic gas should progressively strip them of their own star forming material. In this view, the large spiral galaxy just seen peeking above the bottom edge is an unrelated foreground galaxy a mere 35 million light-years distant.



2000 This weekend, the annual Perseid Meteor Shower reaches its maximum. Grains of cosmic sand and gravel shed from Comet Swift-Tuttle will streak across the sky as they vaporize during entry into Earth's atmosphere. The Perseids result from the yearly crossing of the Earth through Comet Swift-Tuttle's orbit. The Perseids are typically the most active meteor shower of the year. In a clear dark sky, an observer might see a meteor a minute near peak times, but this year a bright moon will overwhelm the glow from many perseid meteors until moonset in the early morning hours. Pictured above is a Perseid meteor from 1993. The colors are representative but digitally enhanced. As the meteor streaked across the night sky, different excited atoms emitted different colors of light. The origin of the green tinge visible at the right is currently unknown, however, and might result from oxygen in Earth's atmosphere. Perseid meteors can best be seen from a relaxing position, away from lights, just before the dawn twilight.

1999 Last October the Space Shuttle Discovery deployed Spartan 201, a spacecraft that monitored the corona of the Sun. Instruments on Spartan 201 were used to estimate the density of electrons emitted into the solar corona, calibrate data from the Solar and Heliospheric Observatory (SOHO) satellite, and study how the Sun is changing as it reaches maximum activity over the next few years. Pictured above, the space shuttle's robot arm (top left) releases Spartan (center) into space. The tail fin of the space shuttle is visible on the right, while the Earth hovers in the background. Spartan floated near the shuttle for two days before it was picked up again and returned to Earth.



1996 Spiral galaxy M65 is a normal spiral galaxy not unlike our own Milky Way. In fact, M65 is a typical spiral galaxy of a type that could be found anywhere in the local universe. Given a morphological type of "Sa", M65 shows tightly wrapped spiral arms and a large nuclear central bulge. The central bulge stars are older and redder than disk stars, which appear more blue. Stars in the bulge of the our own Milky Way Galaxy are also typically older and redder than stars in the disk where our Sun resides. M65 is a member of the Leo Triplet of galaxies, along with its neighbors M66 and NGC 3628. Although it appears that M65's gravity has distorted M66's symmetry, M65's symmetry seems unaffected by M66. M65 is located roughly 35 million light years away, so that light recorded today left after the fall of the dinosaurs but when many land mammals were just evolving on Earth.

1995 Space Shuttle Atlantis lands at Edwards Air Force Base in California. The Space Shuttle is the first orbital space vehicle to land on a runway like an airplane. Space Shuttles sometimes have the option of landing in White Sands, New Mexico or at the Shuttle Landing Facility at the Kennedy Space Center in Florida. The runways the shuttles land on are among the longest in the world. Shuttles that do not land in Florida must generally be strapped to the back of a 747 airplane and flown back.

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— Garrison Keillor