Image of the Week archive
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The ghostly blue object is Abell 55, a planetary nebula. A planetary nebula is a glowing ball of gas powered by a very hot star in the center. The nebula is thought to form near the end of a star's life when the surface layers of the stars are ejected into space, leaving behind the hot central core. In the distant future, the nebula will disperse and the remnant of stellar core will cool down and become a white dwarf. The bright star in the upper left corner of the picture is probably unrelated. (Caption by Steve Kent) |
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Arp 214 This object is also known as NGC 3718. It is a highly disturbed galaxy and is likely the result of a glancing collision with its neighbor NGC 3792 (not visible) some time in the recent past. The reddish band across the center is caused by interstellar dust in front of the galaxy preferentially absorbing blue light. The central bulge of the galaxy (burned out in this exposure) harbors a nucleus filled with ionized gas moving at heigh velocities. (Caption by Steve Kent) |
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The object of interest in this image is a set of faint blue, gree, and
red streaks in the upper half of the picture. This object is an asteroid
passing close to the earth at high angular velocity. It moved from right to
left during the 5 minutes that this image was taken. Since each piece of
the sky is imaged in 5 filters in succession, the object showed up in
different location in each of the different filters. Only 3 of the 5
filters are used to make this image, giving rise to the 3-colored streaks.
Near earth objects are rocks ranging in size from meters to kilometers. These objects are very important because of their likelihood of impacting the Earth. The photometric data provided by SDSS will be invaluable for linking near earth objects to their parent populations. Possible places they may have come from include the asteroid belt and extinct cometary nuclei. (Caption by Steve Kent, Tom Quinn) |
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The bluish object in the image on the left is a quasar recently
discovered by the SDSS. Beneath it is a spectrum showing the
characteristic pattern of emission lines at a redshift z = 1.524. Naohisa
Inada from the Institute of Cosmic Ray Research in Japan noticed that the
image was slightly extended and called out its attention to his SDSS
colleagues. Scott Burles of MIT contacted his colleague Paul Schechter,
who obtained a higher resolution image, shown in the upper right, using
the Magellan 6.5-m telescope in Chile. Amazingly, the object breaks up
into 4 components. The interpretation is that the quasar light passes
close by an unrelated foreground galaxy whose gravitational field is
strong enough to deflect the path of the light, causing the quasar to
appear to be at a position different from its true position. The lensing
in the object is strong enough that the image of the quasar is broken up
into three components. This configuration is actually rather unusual,
because gravitationally lensed quasars most commonly have an even number
of components. The redshift of the lensing galaxy is not known. (Caption by Steve Kent) |
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Einstein Cross Gravitational Lens The bluish object in the image on the left is a quasar recently discovered by the SDSS. Beneath it is a spectrum showing the characteristic pattern of emission lines at a redshift z = 2.446. Scott Burles obtained a higher resolution image, shown in the upper right, using the Magellan 6.5 m telescope in Chile. Amazingly, the object breaks up into 5 compnonents. The interpretation is that the quasar light passes close by an unrelated foreground galaxy whose gravitational field is strong enough to deflect the path of the light, causing the quasar to appear to be at a position different from its true position. The lensing in this object is strong engouth that the image of the quasar is broken up into 4 componenets, forming a pattern called the "Einstein Cross" centered on theimage of teh faint lensing galaxy. The redshift of the lensing galaxy is not known for sure but is thought to be z = 0.54. (Caption by Steve Kent) |
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Messier 101 The galaxy M101 (NGC 5457) is a spectacular spiral galaxy in the constellation Ursa Major. This galaxy is undergoing vigorous star formation, which gives rise to the overall bluish color. The blue and blue-green knots in the spiral arms are HII regions where newly formed hot stars are ionizing the gas clouds from which they formed. The galaxy is one of the most luminous spirals in the nearby universe. It is a favorite object for study by astronomers. (Caption by Steve Kent) |
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Globular Cluster Messier 2 This impressive object is the globular cluster Messier 2, located in the constellation of Aquarius. It is also known as NGC 7089. A globular cluster like M2 contains about a million stars and is located in the halo of our Milky Way galaxy. It is thoguht that the globulars are among the oldest objects in the Galaxy - the stars have ages of several billion years, and they conatin only a small fraction of heavy elements such as oxygen and iron compared with younger stars such as the sun. The Milky Way has of order 100 globular clusters in its halo. (Caption by Steve Kent) |
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Messier 51, The Whirlpool Galaxy Messier 51 (also known as NGC 5194) is a classic 2-armed spiral galaxy whose vivid dust lanes and star forming regions give it a grandeur that makes it a favoritye object for astronomical photographers. The companion galaxy, NGC 5195, is slightly behind M51, as is evidenced by the dust lanes from M51 silouhetted against its neighbor. The two galaxies are interacting gravitationally, and NGC 5195 is surrounded by a spray of stars disloged by the gravitational tidal forces of M51. The galaxies are located in the constellation Canes Venatici. This picture is actually a mosaic made from two separate images
obtained on different nights. The data are calibrated so well that
the line where the two images join is invisible. |
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This picture shows the trail of a meteor entering the earth's
atmosphere that passed through the field of view of the 2.5-m telescope.
Although the meteor is dozens of miles up in the atmosphere, it is still
close enough to be significantly out of focus; the width of the trail can
be used to indicate the meteor's altitude. This meteor was unusual in that
material shed by the meteor left prominent flares to the side of the trail;
most meteors leave only the bright central trail. The green color is not
the trud color of the meteor but instead is due to the meteor passing by
just one of the 5 filters in the SDSS camera. (Caption by Steve Kent) |
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NGC 2775 This spiral galaxy is classified as a type Sab, which means that it has a relatively large bulge and thin, tightly wound spiral arms. The arms, in fact, are little more than stretches of short segments that cannot be connected into any global pattern. The galaxy has little dust and gas, making it easy to see background galaxies, such as a small group to the lower right. (Caption by Steve Kent) |
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NGC 2859 - The Ring Galaxy This galaxy is notable for having both a bar in its disk and an outer ring structure. Bars are fairly common in disk galaxies, with upwards of 1/2 of all such galaxies having bars. The outer ring is a less common feature but is thought to be caused by gas reacting to the gravitational force of the bar at specific locations in the galaxy called "resonances". NGC 2859 is located in the constellation Leo Minor. (Caption by Steve Kent) |
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NGC 3184 - Face-on Spiral Galaxy THis galaxy is a classic face-on spiral in the constellation Ursa Major (the Big Bear). It is classified as type Sc, which means that it has a small, central bulge and a relatively open, well-defined spiral pattern. The galaxy is at a distance of approximately 9 Megaparsecs, which puts it about halfway between our own Milky Way galaxy and the nearest rich cluster of galaxies in the constellation Virgo. A supernova was observed in 1999, which is a common event in galaxies like NGC 3184 that are experiencing vigorous star formation. (Caption by Steve Kent) |
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NGC 3359 is a spiral galaxy with an open spiral pattern and a bar, so
it is classified as type SB(rs)c. It is located in the constellation Ursa
Major (the Big Bear). The strong blue color indicates that
vigorous star formation is still occurring in the galaxy. This galaxy
is at a redshift of z = 0.003382, which corresponds to a distance of
15 Mpc, relatively close by. (Caption by Steve Kent, Mark Schaffer, and Lauren Grodnicki) |
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NGC 5746 is a classic spiral galaxy, located in the nearby Virgo
cluster of galaxies. It has a distinct spiral disk and a large "peanut
bulge" core. The peanut bulge is thought to be a thickened bar structure
within the disk of the galaxy, so that the galaxy would be classified as a
barred spiral if viewed face-on. (Caption by Steve Kent) |
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This image of comet 30P/Reinmuth 1 was captured by the Sloan telescope
on Dec. 7, 2002 when the comet happened to lie in the path of the telescope
scan. At this time the comet was about 1.4 astronomical units form the
earth and had a magnitude of 14.5. The comet moved by about 8 arcseconds
during the time that the camera scanned across it, causing the red, green,
and blue images not to line up correctly in the picture.
The comet was discovered by Karl Reinmuth of the Heidelberg Konigstuhl
Observatory in 1928. It has a period of 7 years, which means that it is
classified as a short period comet. It occassionally passes close to
Jupiter, which causes the orbit to be perturbed. Eventually the comet will
either crash into a planet or (more likely) be tossed out of the solar
system due to Jupiter's strong gravitational field. |
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Sextans B is a relatively nearby (1.2 Mpc) irregular galaxy just beyond the Local
Group that contains our Milky Way. The galaxy is close enough that the
brightest blue and red stars are easily visible, along with numerous star
clusters. (Caption by Steve Kent and Mark Schaffer) |
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UGC 5189 This blue, irregular object is almost certainly the result of a collision between two or more galaxies; however, the collision was so violent that it is unclear what the progenitors looked like or even if the remnant will remain a single object. (Caption by Steve Kent) |
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VV150b - Group of Galaxies The 5 brightest galaxies forma compact group of galaxies that likely form a gravitationally bound system. All have velocities of about 8000 km/s. Another name for this group is Arp 322. Tidal interactions give rise to the streamers of material that appear to connect some of the galaxies. By accurately measuring the velocities of the galaxies with respect to one another, it is possible to estimate the total mass of such groups. (Caption by Steve Kent) |
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Abell 1576 is a rich cluster of galaxies (Abell richness class 3, 130-199 cluster members) in the constellation of Ursa Major. Its reshift z=.30 puts this cluster at a distance of about 5 billion light years: the light we see was emitted when the universe was ~35% younger than now. The image, which is the rgb composite of the SDSS g-r-i bands, shows very clearly the presence of a double nucleus in the cD envelope, in the center of the cluster potential well. It is very interesting to note how redshift affects colours: cluster galaxies are much redder than the galaxies in the foreground (e.g. the spheroid at the bottom of the frame). THe driving cause here is the fact that, at z>~0.30, the g band (i.e. the blue component of the image) maps the spectral region shortward of the Balmer break at 4000 Angstrom, where flux is particularly suppressed. (Caption by Stefano Zibetti) |
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10/26/03 - This object is a reflection nebula in the constellation Cepheus. The central star, which has catalog number BD+69 1231, is a recently formed blue giant that is surrounded by a cloud of interstellar dust. The light of the star is reflected from the dust, giving this object its shimmering appearance. The dust is clumped into filaments and loops which are clearly visible in the image. (Caption by Steve Kent) |
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12/15/03 - This object is the planetary nebula G164.8+31.1, located in the constellation of Lynx. The digits in the name give the location of the object in Galactic coordinates. The nebula is made of diffuse, ionized gas that is at a temperature of about 10,000 degrees Kelvin. The green color is due to strong emission lines from hydrogen and nitrogen atoms. The bluish tint towards the center is due to emission from doubly ionized oxygen atoms. The small, bluish star in the center is emitting intense ultraviolet radiation that ionizes and excites the nebula. At some time in the future, the nebula will dissipate and disappear, while the central star will settle down and become a white dwarf star. (Caption by Steve Kent) |