The Double Cluster is composed of open clusters NGC 869 and NGC 884, both of which lie 7500 light-years
distant in the constellation Perseus. They can be spotted with the naked eye under good viewing conditions,
or quite easily with a pair of binoculars.
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This is one of the largest known globular clusters in the Milky Way galaxy.
Under good seeing conditions and dark skies, binoculars can quite easily distinguish
this object as a cluster. It is located about 33,000 light-years away from us toward the constellation Aquarius.
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This ball of 500,000 stars is approximately 100 light-years across. From a galactic perspective, this
cluster is passing over our heads (galactic north), and is one of the first bright clusters to become
available before the others closer to the galactic center. Some people believe that this cluster
inspired Charles Messier to begin systematically recording the location of deep sky objects that
through his telescope appeared as nebulous. Charles Messier was interested in finding comets and
considered these non-comet fuzzies to be a bit of a distraction. Even with modest equipment today,
the true nature of these objects are easily revealed.
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M5 is arguably one of the best globular clusters in the sky visible from the northern hemisphere.
These balls of stars (upwards of a million members) orbit our galaxy tens of thousands of light years
distant. This particular cluster is approximately 26,000 light years away and is estimated to be 13 BILLION
years old (*whew*).
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Messier 7, or the Ptolmey Cluster, can easily be found in the constellation Scorpius with the
naked eye under dark skies. It makes a great binocular and telescope object. Open clusters that
we view are generally much closer than globular clusters. Rather than being tens of thousands of
light-years away, this cluster is only 980 light-years distant and 25 light-years across.
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This cluster looks very much like many of the other bright examples in the Messier catalogue.
Though often overlooked, this one and M12 are spectacular jewels in the direction of Ophiuchus.
From our vantage point we look at these clusters just over (north) of the galactic plane.
M10 is estimated to be 16,000 light-years away (perhaps 70 light-years in diameter).
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M11 got its nickname, the Wild Duck Cluster, from Admiral Smyth. His view in 1835 seemed to elicit visions
of wild ducks flying in the distant sky. With the growth of large cities, seeing similar flocks fill the
sky are most rare indeed. This is certainly one of the more compact examples of open star clusters with
members numbering nearly 3000 stars. The oldest stars in this cluster are only 220 million years old,
indicating that this cluster is still quite young. But the true vision of wild ducks can be better
glimpsed by our understanding of these starsʼ orbits. A picture like this is only a snapshot of the
convoluted and complex orbital interactions these stars dance through time. Each star affects the other
in their messy mingle about each other; as ducks they would appear to be very confused. A stargazer on a
planet orbiting one of these stars would see a sky filled with hundreds of nearly identical
first magnitude stars. Image trying to keep track of their names!
M13 is certainly the most famous globular cluster in the sky of the northern hemisphere.
The visual appeal of a cluster like this is unmatched for most deep sky objects. This sphere
of over 300,000 stars looks something like scattered diamonds in even relatively small telescopes.
The stars in a cluster like this orbit one another wildly as they are crammed into a ball 100
light-years across. In addition to the number of stars, the ages of the suns in this cluster
are some of the oldest in the universe-- perhaps 12-14 billion years old! M13 is easily found
in the constellation of Hercules and can even be glimpsed with an unaided eye under dark skies.
Also check out the background galaxy NGC 6207 in the same direction as M13. Globular clusters
orbit the center of the galaxy. M13 is currently about 22,000 light-years away from us.
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Spilled salt. This is what M14 resembles through a moderate sized telescope under dark skies.
This particular cluster is not quite as concentrated in density towards its center.
Some clusters such as M15 have a very tight central region.
What is truly interesting about M14 is that this jumble of stars actually helped astronomers
put the pieces of a puzzle together. One of the central stars here is very special.
It is called a "CH star" because its atmosphere has carbon-hydrogen molecules. Everything
heavier than hydrogen, helium, and lithium is basically created in the centers of stars
through nuclear fusion or as a by-product of supernovae explosions-- the ultimate stellar
crucible. Generally small stars do not reveal what heavy elements are contained in their
cores until they dredge up these materials near the ends of their lives (and later expel
them in the form of a planetary nebula). However this star shown below is not old enough
to have done this! Thus astronomers wondered why should CH stars have carbon in their atmospheres?
An answer was soon found when astronomers discovered that all CH stars are part of a binary
system. One of the stars, near the end of its life, dredges up its stellar ashes of nuclear
fusion and proceeds to expel it into space. Much of this material is dumped onto the other
companion. So, although too young to have carbon, this companion gets a good helping from its dying friend.
What is so special about finding a CH (binary) star in M14 (or any globular cluster) is that
these stars are first generation stars of our universe. There are very few planetary nebulae
to be found in globular clusters, so studying the nuclear products of these stars has been
difficult. But here, using this CH star, astronomers can directly examine the make up of one
of these stars by examining the atmosphere of the other!
M22 is a truly spectacular example of a star cluster since it is very near and, as we view it,
toward the center of the galaxy. Thus, when M22 is observed we see hundreds of thousands of its
constituents as well as a myriad of stars in the foreground and background (the ultimate of stars
upon stars). M22 is estimated to be 10,000 light-years away and around 65 light-years across.
This cluster can be seen easily in binoculars near the star atop the "teapot" asterism of Sagittarius.
M24, NGC 6590, and IC1284:
The Sagittarius Star Cloud
An image like this shows that our galaxy is always "partly cloudy." Not unlike Earthly clouds that
block parts of the sky (say on a starry night), tremendous clouds of gas and dust obscure the things
that are beyond them. However, breaks in these galactic clouds can also be seen, even towards the
densest part of our galaxy. M24 is the large oval collection of bluish stars that stands out among
the others in the right of this picture. To look at this stellar association of young and bright
stars is to peer through a break in the obscuring clouds to places much deeper towards an inner
spiral arm. The stars of M24 are many thousands of light-years away (perhaps 10,000). The northern
part of this star cloud boasts several dark nebula that provides contrast for all of the stars in
the background. Near the lower center of the frame, IC 1284 glows bright red, while NGC 6590 scatters bluish
light around a few bright stars.
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M44 is a beautiful open cluster in the center of the constellation Cancer. It can be seen
as a faint nebulosity with the naked eye under good viewing conditions, and is easily
resolved with a small pair of binoculars or telescope. In fact, this is one object frequently
better suited for binoculars compared to a telescope, due to its large angular extent.
Distance estimates for this cluster vary from 500-600 light-years away, but astronomers are
fairly confident in an age of about 600 million years old.
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This very bright open cluster has a large angular extent, making it a great binocular object.
If you viewed this object through a large telescope, you would only see a few stars, not the
entire cluster. Perhaps the most famous open cluster, this is easily visible with the naked eye.
In fact, many children with great eyesight look toward this cluster and mistake it for the
Little Dipper. When you view this cluster through binoculars, it does in fact look like a measuring cup.
M45, or the Pleiades, or the Seven Sisters, or Subaru if you're in Japan, are all names for this
cluster. In Greek mythology, the Seven Sisters were the daughters of Atlas and Pleione, and the
half-sisters of Hyades. It is interesting to note that when counting the brightest stars in this
cluster, most people only come up with six. Some versions of the mythology describe a missing sister,
the reason why we do not see a seventh bright star is unknown.
The bright blue, massive stars that make up this cluster are less than 100 million years old.
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M53 is relatively lonely in the constellation of Coma Berenices. The nearby neighbor M3 is
often observed instead. However this cluster deserves a brief visit in the telescope at least once.
Although dim in appearance, this cluster is actually quite large at 250 light-years in diameter.
Its faintness and small size are attributed to its remote distance of 60,000 light years.
M79 is kind of a pathetic globular cluster-- I say this with emotion based on its appearance compared
to other Messier globular clusters. However the winter sky has little to offer in terms of these clusters;
M79 is just about it. These clusters orbit the center of the galaxy, and the winter sky (toward Orion)
is in the opposite direction. There is a good reason that M79 is so dim-- it is located approximately
41,000 light-years away and is one of the few that exists outside the orbit of the Sun. So why is
this cluster not located with the others? This globular was possibly a component to a smaller, dwarf
galaxy that is currently interacting with the Milky Way. In a sense, we may have stolen this cluster
from another galaxy! Due to its southern location and distance, it is very difficult to appreciate
visually through a telescope. CCD images such as this begin to reveal the true nature and beauty of
this sphere of stars.
This globular cluster has the distinction of being one of the most concentrated in our
galaxy (NGC 1851 is another good example). This cluster is estimated to be 26,000 light-years away
and perhaps 70 light-years in diameter.
This beautiful globular cluster is bright and can make a great binocular object under good viewing
conditions. However, it is very often skipped in favor of its neighbor, M13. M92 is one of the
oldest known globular clusters, at over 14 billion years in age.
M107 is the last globular cluster in Messier's catalogue of 110 objects. Messier's catalogue originally
included only 103 objects. Upon discovering notes from Messier suggesting that he did indeed know of
several other deep sky nebulae, clusters and galaxies, astronomers added seven extra objects including
the globular cluster M107. M107 lies about 21,000 light-years away in the constellation Ophiuchus.
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NGC 206 is a large OB association of very luminous stars in the outer spiral arms of the Andromeda Galaxy.
It is by far one of the most active collections of such stars to be found in our local neighborhood.
Studies in this region of the Andromeda galaxy seem to indicate that this part of its spiral arm was
unusually dense with gas, the building blocks of these stars. Some theories even assert that this region
is actually the blending of two spiral arms which would represent the compression of this gas into a
denser region and fuel the extreme star formation that we see today. The gravitational influence of this
gas/star cluster region actually affects the overall structure of the disk of the Andromeda galaxy.
These stars formed around 20 million years ago and have produced stellar winds that have now blown
away much of their natal gas. Pictures of the Andromeda galaxy in the radio wavelengths of light (21cm line)
show a large hole (1200 x 2400 light-years) that surrounds this cluster. Other images of ionized hydrogen
gas show a glowing bubble whose brightness agrees with the number of illuminating stars in the cluster.
Had the stars not blown away the gas (2 million solar masses of it) many more stars could have formed here.
NGC 457 is an open cluster located in the constellation Cassieopeia. It is easily found in small
telescopes, and a favorite for amateur astronomers who can imagine the nicknames of Owl Cluster and ET.
The two bright stars in the upper left make up the eyes of ET.
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This is a relatively young open cluster located in the constellation Orion. It is surprisingly
metal-poor (astronomers consider anything heavier than helium to be a metal). Stars in open
clusters are typically formed from the remnants of several previously existing stars. As each
star fuses new metals and expels them at the end of its lifetime, new stars are created with
higher metallicities than existed previously. This cluster on the other hand, seems to have
formed a bit outside of our galactic plane from a metal-poor gas cloud.
NGC 2266 is a relatively "old" star cluster comprising stars of around 1 billion years in age.
Many of its members are quite evolved, having reached the red giant stage of their lives.
Our own sun will become a red giant when it is around 10 billion years old. This means that
many of the evolved stars in this cluster (the yellow/orange ones) are much more massive than
our own Sun. The more massive a star is, the shorter its life.
In addition, this particular cluster lies several thousand light-years above the galactic plane.
Most galactic star clusters form and disband within the disk of our galaxy. NGC 2266 can therefore
be an interesting laboratory for astronomers since its stars have been unaffected by the hubbub of
the rest of the galaxy. How did NGC 2266 arrive at its position in the galaxy? How does the composition
of gas in the stars of this cluster differ from the current composition of the mixed gas in the
disk of the galaxy? How is this cluster similar to others of the same type? These are the kinds of
questions that astronomers would like to answer when observing this otherwise sparkling set of jewels.
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NGC 2419 is often called the "Intergalactic Wanderer" because of its very remote distance from our
galaxy (in excess of 250,000 light-years away). It could very well be that this cluster some how
attained an escape velocity and has left the gravitational confines of our Milky Way. The view looking
back at us must be remarkable. This cluster is intrinsically quite bright and if it was at the same
distance as famous clusters like M13 or M5 it would outshine them! However, the reality is that
this cluster only hints at its blazing glory with the aid of sensitive CCD cameras and telescopes.
Minimum credit line: Doug Matthews and Charles Betts/Adam Block/NOAO/AURA/NSF
The name "Omega Centauri" should hint that this particular cluster is quite special. As viewed
from Earth, Omega Cen (as it is often called) is certainly one of the most dazzling of globular
clusters that orbits our galaxy. Before the use of good telescopes (and optics) this cluster
was known as a "star" in the constellation of Centaurus (and hence the name). However, under
a dark sky this cluster certainly hints at more. It takes on the appearance of fuzzy patch of
light--not unlike many other closer star clusters (M41, M44, M35, etc). However, at a distance
of 20,000 lights-years away, it is only due to the sheer number of stars--easily more than
500,000--that we can see it this easily. A telescopic view reveals the sparkling glitter
shown to the left. From Kitt Peak, this cluster barely climbs more than 10 degrees above
the horizon. As such, the image quality isn't great, but the overall impression of this
cluster is maintained. Interestingly, Omega Cen is one of the few clusters that is currently
passing directly through the plane of our galaxy.
The name "Omega Centauri" should hint that this particular cluster is quite special. As viewed from
Earth, Omega Cen (as it is often called) is certainly one of the most dazzling of globular clusters
that orbits our galaxy. Before the use of good telescopes (and optics) this cluster was known as
a "star" in the constellation of Centaurus (and hence the name). However, under a dark sky this
cluster certainly hints at more. It takes on the appearance of fuzzy patch of light- not unlike
many other closer star clusters (M41, M44, M35, etc). However, at a distance of 20,000 light-years
away, it is only due to the sheer number of stars--easily more than 500,000--that we can
see it this easily. A telescopic view reveals the sparkling glitter shown to the left. From
Kitt Peak, this cluster barely climbs more than 10 degrees above the horizon. As such, the
image quality isn't great, but the overall impression of this cluster is maintained. Interestingly,
Omega Cen is one of the few clusters that is currently passing directly through the plane of our galaxy.