Astronomy Picture of the Day (APOD) is a website provided by NASA and Michigan Technological University (MTU). According to the website, "Each day a different image or photograph of our universe is featured, along with a brief explanation written by a professional astronomer." The photograph does not necessarily correspond to a celestial event on the exact day that it is displayed, and images are sometimes repeated. However, the pictures and descriptions often relate to current events in astronomy and space exploration. The text has several hyperlinks to more pictures and websites for more information. The images are either visible spectrum photographs, images taken at non-visible wavelengths and displayed in false color, video footage, animations, artist’s conceptions, or micrographs that relate to space or cosmology. Past images are stored in the APOD Archive, with the first image appearing on June 16, 1995. This initiative has received support from NASA, the National Science Foundation, and MTU. The images are sometimes authored by people or organizations outside NASA, and therefore APOD images are often copyrighted, unlike many other NASA image galleries.
APOD was presented at a meeting of the American Astronomical Society in 1996. Its practice of using hypertext was analyzed in a paper in 2000. It received a Scientific American Sci/Tech Web Award in 2001. In 2002, the website was featured in an interview with Nemiroff on CNN Saturday Morning News. In 2003, the two authors published a book titled The Universe: 365 Days from Harry N. Abrams, which is a collection of the best images from APOD as a hardcover "coffee table" style book. APOD was the Featured Collection in the November 2004 issue of D-Lib Magazine.
Dr. Robert J. Nemiroff and Dr. Jerry T. Bonnell were awarded the 2015 Klumpke-Roberts Award by the Astronomical Society of the Pacific "for outstanding contributions to public understanding and appreciation of astronomy" for their work on APOD.
|Astronomy Picture of the Day|
The APOD website on 31 December 2016, displaying that day's astronomy picture of Trifid Nebula in infrared
Type of site
|Available in||English (primary)|
|Owner||NASA and MTU|
|Created by||Robert J. Nemiroff and Jerry Bonnell|
|Launched||16 June 1995|
The Antennae Galaxies, also known as NGC 4038/NGC 4039, are a pair of interacting galaxies in the constellation Corvus. They are currently going through a starburst phase, in which the collision of clouds of gas and dust, with entangled magnetic fields, causes rapid star formation. They were discovered by William Herschel in 1785.Baade's Window
Baade's Window is an area of the sky with relatively low amounts of interstellar "dust" along the line of sight from the Earth. This area is considered an observational "window" as the normally obscured Galactic Center of the Milky Way is visible in this direction. It is named for astronomer Walter Baade who first recognized its significance. This area corresponds to one of the brightest visible patches of the Milky Way.Bipolar nebula
A bipolar nebula is a distinctive nebular formation characterized by an axially symmetric bi-lobed appearance.
Many, but not all, planetary nebulae exhibit an observed bipolar structure. It may be that the two types of nebulae are directly related, one preceding or superseding the other in the evolution of the nebula.Candor Chasma
Candor Chasma is one of the largest canyons in the Valles Marineris canyon system on Mars. The feature is geographically divided into two halves: East and West Candor Chasmas, respectively. It is unclear how the canyon originally formed; one theory is that it was expanded and deepened by tectonic processes similar to a graben, while another suggests that it was formed by subsurface water erosion similar to a karst. MRO discovered sulfates, hydrated sulfates, and iron oxides in Candor Chasma.
One of the pictures below shows branched channels. Many places on Mars show channels of different sizes. Many of these channels probably carried water, at least for a time. The climate of Mars may have been such in the past that water ran on its surface. It has been known for some time that Mars undergoes many large changes in its tilt or obliquity because its two small moons lack the gravity to stabilize it, as our moon stabilizes Earth; at times the tilt of Mars has even been greater than 80 degreesNGC 1818
NGC 1818 is a young globular cluster in the Large Magellanic Cloud. It was discovered by astronomer James Dunlop in 1826.NGC 1893
NGC 1893 is an open cluster in the constellation Auriga. It is about 3,280 light years away. The star cluster is embedded in the HII region IC 410.Images of the star cluster by the Chandra X-ray Observatory suggest that it contains approximately 4600 young stellar objects.NGC 2170
NGC 2170 is a reflection nebula in the constellation Monoceros. It was discovered on October 16, 1784 by William Herschel.NGC 2440
NGC 2440 is a planetary nebula, one of many in our galaxy. Its central star, HD62166, is possibly the hottest known white dwarf. The nebula is situated in the constellation Puppis.
It was discovered by William Herschel on March 4, 1790. He described it as "a beautiful planetary nebula of a considerable degree of brightness, not very well defined." The nebula is located about 1.23 kiloparsecs (3.79×1019 m) or about 4,000 light years from the Sun.NGC 474
NGC 474 is an elliptical galaxy about 100 million light years distant in the constellation Pisces. This large galaxy is known to possess tidal tails, although their origins remain unknown.NGC 6752
NGC 6752 (also known as Caldwell 93) is a globular cluster in the constellation Pavo. It is the third-brightest in the sky, after Omega Centauri and 47 Tucanae, and is best seen from June to October in the Northern Hemisphere.NGC 6752 was first identified by one James Dunlop of Parramatta on 30 June 1826, who described it as an irregular bright nebula which could be resolved into a cluster of many stars, highly compressed at the centre. This corresponds with a core region densely populated with stars around 1.3 light-years in diameter, which indicates it has undergone core collapse. The cluster lies around 13,000 light-years distant and is one of the closer globular clusters to Earth. It also lies 17,000 light-years away from the galactic centre. It belongs to Shapley–Sawyer Concentration Class VI, namely of intermediate density, and has been calculated to be 11.78 billion years old. There are a large number of binary stars in the system, as well as blue stragglers, which are likely to have been formed by collisions and mergers of smaller stars. The NASA website "Astronomy Picture of the Day" notes that it holds over 100,000 stars in a sphere about 100 light-years in diameter.The apparent magnitude of the cluster is 5.4, so it can be seen with the unaided eye. However this depends on good viewing conditions with a minimum of light pollution. With binoculars it can be seen to cover an area three quarters the size of the full moon. It lies 1.5 degrees east of 5th-magnitude Omega Pavonis. The nearest bright star is Peacock, which lies 3.25 degrees north and 9.25 degrees east.Six X-ray sources have been identified in the cluster's core by the Chandra X-Ray Observatory.NGC 7008
NGC 7008 (PK 93+5.2), also known as the Fetus Nebula is a planetary nebula with a diameter of approximately 1 light-year located at a distance of 2800 light years in northern Cygnus. It was discovered by William Herschel in 1787, in Slough, England. NGC 7008 (H I-192) is included in the Astronomical League's Herschel 400 observing program.NGC 7635
NGC 7635, also known as the Bubble Nebula, Sharpless 162, or Caldwell 11, is an H II region emission nebula in the constellation Cassiopeia. It lies close to the direction of the open cluster Messier 52. The "bubble" is created by the stellar wind from a massive hot, 8.7 magnitude young central star, SAO 20575 (BD+60°2522). The nebula is near a giant molecular cloud which contains the expansion of the bubble nebula while itself being excited by the hot central star, causing it to glow. It was discovered in 1787 by William Herschel. The star BD+60°2522 is thought to have a mass of about 44 M☉.Nereus (crater)
Nereus is a small impact crater lying situated within the Margaritifer Sinus quadrangle (MC-19) region of the planet Mars with a diameter of about 10 metres (33 ft). It is located just south of the planet's equator on the relatively smooth Meridiani Planum (plain).It was discovered by the Opportunity Mars rover on Sol 2010 (2009-09-19), being noticed because it is surrounded by jagged rocks, and was the Astronomy Picture of the Day for 2009-10-19.
It is named for Nereus, a Greek god who lived with the Nereids in the Aegean Sea.Pollack (Martian crater)
Pollack is an impact crater in the Sinus Sabaeus quadrangle of Mars, located at 7.9° S and 334.8° W. It measures 96 kilometers in diameter and was named after James B. Pollack, an American astrophysicist (1938–1994).
Pollack Crater contains a large light toned deposit that was once thought to be a salt deposit. However, the surrounding rocks are exceptionally dark and that makes this deposit appear white.Puckett Observatory
Puckett Observatory is a private astronomical observatory located in the state of Georgia. It is owned and operated by Tim Puckett. Its primary observation goals are the study of comets and the discovery of supernovae. To facilitate the latter goal it sponsors the Puckett Observatory World Supernova Search whose astronomers have discovered 369 supernovae.Robert J. Nemiroff
Dr. Robert J. Nemiroff is a Professor of Physics at Michigan Technological University. He received his Ph.D. from the University of Pennsylvania in Astronomy and Astrophysics in 1987 and his B.S. from Lehigh University in Engineering Physics in 1982. He is an active researcher with interests that include gamma-ray bursts, gravitational lensing, and cosmology, and is the cofounder and coeditor of Astronomy Picture of the Day (APOD), the home page of which receives over a million hits a day, approximately 20% of nasa.gov traffic. He is married and has one daughter.Solar eclipses on Jupiter
Solar eclipses on Jupiter occur when any of the natural satellites of Jupiter pass in front of the Sun as seen from the planet Jupiter.
For bodies which appear smaller in angular diameter than the Sun, the proper term would be a transit. For bodies which are larger than the apparent size of the Sun, the proper term would be an occultation.
There are five satellites capable of completely occulting the Sun: Amalthea, Io, Europa, Ganymede and Callisto. All of the others are too small or too distant to be able to completely occult the Sun, so can only transit the Sun. Most of the more distant satellites also have orbits that are strongly inclined to the plane of Jupiter's orbit, and would rarely be seen to transit.
When the four largest satellites of Jupiter, the Galilean satellites, occult the Sun, a shadow transit can be seen on the surface of Jupiter which can be observed from Earth in telescopes.
Eclipses of the Sun from Jupiter are not particularly rare, since Jupiter is very large and its axial tilt (which is related to the plane of the orbits of its satellites) is relatively small—indeed, the vast majority of the orbits of all five of the objects capable of occulting the Sun will result in a solar occultation visible from somewhere on Jupiter.
The related phenomenon of satellite eclipses in the shadow of Jupiter has been observed since the time of Giovanni Cassini and Ole Rømer in the mid Seventeenth Century. It was soon noticed that predicted times differed from observed times in a regular way, varying from up to ten minutes early to up to ten minutes late. Rømer used these errors to make the first accurate determination of the speed of light, correctly realizing that the variations were caused by the varying distance between Earth and Jupiter as the two planets moved in their orbits around the Sun.
Spacecraft can be used to observe the solar eclipses on Jupiter; these include Pioneer 10 and Pioneer 11 (1973 and 1974), Voyager 1 and Voyager 2 (1979), Galileo orbiter (1995–2003), Cassini–Huygens (2000) and New Horizons (2007) observed the transits of their moons and its shadows.The World At Night
The World At Night (TWAN) is an international project to produce and present a collection of high-quality photos, videos, and virtual reality (VR) images of the night sky taken at various natural, cultural, and historic locations worldwide.Based on the peacemaking slogan of "One People, One Sky", TWAN aims to demonstrate that humanity is one family when considered under the roof of the night sky. According to its website, "TWAN is a bridge between art, humanity, and science. The eternally peaceful sky looks the same above all the landmarks and symbols of different nations and regions, attesting to the truly unified nature of Earth as a planet rather than an amalgam of human-designated territories."Vela Supernova Remnant
The Vela supernova remnant is a supernova remnant in the southern constellation Vela. Its source Type II supernova exploded approximately 11,000–12,300 years ago (and was about 800 light-years away). The association of the Vela supernova remnant with the Vela pulsar, made by astronomers at the University of Sydney in 1968, was direct observational evidence that supernovae form neutron stars.
The Vela supernova remnant includes NGC 2736. It also overlaps the Puppis Supernova Remnant, which is four times more distant. Both the Puppis and Vela remnants are among the largest and brightest features in the X-ray sky.
The Vela supernova remnant (SNR) is one of the closest known to us. The Geminga pulsar is closer (and also resulted from a supernova), and in 1998 another near-Earth supernova remnant was discovered, RX J0852.0-4622, which from our point of view appears to be contained in the southeastern part of the Vela remnant. One estimate of its distance puts it only 200 parsecs away (about 650 ly), closer than the Vela remnant, and, surprisingly, it seems to have exploded much more recently, in the last thousand years, because it is still radiating gamma rays from the decay of titanium-44. This remnant was not seen earlier because in most wavelengths, it is lost because of the presence of the Vela remnant.