Stellar Families In The Winter Sky - Open Clusters & Associations
This is a great time of the year to look at some of my favorite objects, clusters and associations. Clusters are just that, groups of stars all moving in the same general direction and gravitationally bound in some form. They generally fall into two categories, globular and open. There are big differences between these two types. Globular clusters contain many thousands of members in a roughly spherical shape (hence, globular) and are made up of ancient red stars. They are fairly distant from our Solar System and orbit the core of our galaxy, forming a halo of sorts.
(image by Robert Little)
Open clusters, on the other hand, tend to be made up of much younger stars and contain only a few hundred stars usually (some may contain more than a thousand). Unlike globular clusters, open clusters orbit within the plane of the galaxy and some lie fairly close by (within a few hundred light years).
(image by Robert Little)
Associations, also known as stellar associations or moving groups, are clusters that have dissipated over time. You see, eventually gravitational interaction and a cluster's movement through large molecular clouds cause them to eventually disperse, causing their gravitational interaction to dwindle and eventually to cease affecting them altogether. The remnants of the cluster are stars that move in the same relative direction, though many times the resemblance to an open cluster persists when they are viewed at a distance.
The winter sky, which in early December rises not long after sunset, has three very notable open clusters (well, really, four) and a wonderful stellar association. The most obvious of these are the Pleiades, the famous Seven Sisters of yore, also known as M45 and NGC 1432. The best thing about all of these objects is the ease with which they can be found, though one (or is that two) of them is (are?) a bit more challenging. You need nothing more then patience to look for them on winter nights; that and a thermos of your favorite warm beverage.
Looking very much like an even smaller Dipper (and in fact sometimes confused with the Little Dipper), the Pleiades are the most notable open cluster, even though the brightest star within the cluster is only a modest magnitude 3. There is some confusion as to why this cluster is known as the Seven Sisters, though many astronomers believe it is possible that one of the stars, Pleione, may have been brighter once; however, many people with very acute eyesight are able to see more than seven in near perfect conditions (my best friend says she sees fourteen!). When not viewed directly, though, the Pleiades have a strange glow about them, almost mist like. This is in no certain terms due to the large number of faint stars all concentrated into an area roughly four Moon diameters in size (around 2°). The truth is that there are many more than six or seven or fourteen stars in the Pleiades; there are, in fact, several hundred. With binoculars, it is easy to see as many as fifty, but you do not want to use too high a magnification to view this set of jewels. It is best viewed through binoculars or very low power (rich field) telescopes.
The brightest members of the Pleiades, and in fact most open clusters, are blue giants, massive, brilliantly burning stars that are very short lived. Because of their mass, they burn up most of their fuel in very little time, typically no more than a few tens of millions of years, and they go out as supernovae. Many of the stars within the Pleiades are not visible in binoculars, so the sheer number that actually make up this beautiful group remain hidden, only manifesting their presence telescopically or with larger aperture instruments.
As this small cluster moves along through space at a distance of over four hundred light years, it is passing through a cloud of dust. While not readily visible through binoculars (though possibly faintly visible to the naked eye using averted vision), this cloud adds to the beauty of the Pleiades when photographed, like splendid cirrus clouds floating amongst these fine stars.
(image courtesy Royal Observatory Edinburgh / David Malin)
Sitting nearby but not as conspicuous is another open cluster, the Hyades, disguised as the head of Taurus the Bull. When you look towards them, the first star that jumps out is the Aldebaran, the angry red eye of Taurus. This brilliant star is actually less than half the distance of the cluster, less than seventy light years out and is not associated with the cluster.
They Hyades themselves are actually very similar to the Pleiades though much older, on the order of half a billion years, and are more spread out as they have aged and drifted. Because of this fact, they are not as conspicuous a cluster, though a view through binoculars gives it away and shows its true nature. As with the Pleiades, there are many more faint members, giving a total of perhaps a couple hundred stars in total.
As impressive as the Pleiades but many times more distant lie two massive clusters, the famed Double Cluster in Perseus.
Lying several thousand light years away, the Double Cluster, like the Pleiades and the Hyades, is made up of blue supergiant stars; however, due to its distance, even on the most clear nights it appears as strictly two small fuzzy patches in the night sky, lying halfway between Cassiopeia and Perseus. While easy to find in binoculars, this twin cluster is best viewed telescopically, though even a modest telescope (as small as 50 mm) will bring it to life. Many astronomers feel that the two groups that make up the Double Cluster are actually gravitationally linked, that they actually influence each other and perhaps even share a common origin.
Also lying within the constellation of Perseus is a sight that surprised me the first time I saw it, a dazzling array of blue white stars sitting near Mirfak (Alpha Persei), the brightest star within Perseus. This is not a cluster but a stellar association, the Perseus III group.
Again, we're back to an object that is best viewed through binoculars. An association can best be thought of as a cluster that has matured, and like a family whose members have grown up, has begun to move apart, no longer influencing each other and their courses. The night sky actually has many associations; our Sun sits on the outskirts of a massive one, in fact. The only clue that gives away the presence of many associations is shared relative motion by member stars. Because of this, many associations are simply lost to the night. Luckily for us, the Perseus III group is distant enough to all share the same region of space when viewed from our Solar System. As viewed at 7x, the number of stars (around thirty can easily be made out under the right conditions) is startling, especially considering the proximity to other, apparently brighter (though actually much closer) stars.
The Solar System... In Ed Austin Regional Park
At my Freewebs site I've uploaded a page that shows a model of the Solar System built alongside Huffman Boulevard in Jacksonville's Southside. Looking to teach young people in various parts of our vast city, I've found myself looking at other parks and places to set up the same model, and Ed Austin Regional Park actually lends itself rather nicely. These Google Maps images (taken while improvements were still being made to the park) show how easy it is and how the contour of the park lends itself to the task. The Police Athletic League clubhouse actually sits on a rise in this former country club, and if you place our little 142 mm Sun near it, you can fit the entire inner system in the parking lot, while the two largest planets, Jupiter and Saturn, are near the periphery.
How about the rest of the Solar System? Yes, amazingly, you can even get Pluto (STILL a planet in my book!) to lie within the park!
Why is this an ideal setup, though? Basically, the Sun sits higher than many of the other locations I've chosen before. The advantage, simply put, is that the Sun remains readily visible down the entire model; if our little model Sun glowed, it would appear very much as it would from the actual planets themselves, appearing the same size when measured in angular size (though Pluto actually sits beyond a rise going into the park if you set it alongside the main road). While not a straight line (and again the images are a little misleading; the base images were taken during renovations and therefore not accurate), it does provide us with a useful model, one that has marked advantages over the original model laid out in Mandarin Park.
The Vagabond Astronomer will be at the Ed Austin Regional Park starting at 4:00 PM on the 8th of December, 2006, helping students build his model Solar System. Starting at 6:00 PM (after a picnic dinner), we'll move to the west end of the soccer field parking lot with a few telescopes to view those aforementioned clusters and anything else that might attract our attention. Hope to see you there!
(image by Robert Little)(image by Robert Little)The winter sky, which in early December rises not long after sunset, has three very notable open clusters (well, really, four) and a wonderful stellar association. The most obvious of these are the Pleiades, the famous Seven Sisters of yore, also known as M45 and NGC 1432. The best thing about all of these objects is the ease with which they can be found, though one (or is that two) of them is (are?) a bit more challenging. You need nothing more then patience to look for them on winter nights; that and a thermos of your favorite warm beverage.
Looking very much like an even smaller Dipper (and in fact sometimes confused with the Little Dipper), the Pleiades are the most notable open cluster, even though the brightest star within the cluster is only a modest magnitude 3. There is some confusion as to why this cluster is known as the Seven Sisters, though many astronomers believe it is possible that one of the stars, Pleione, may have been brighter once; however, many people with very acute eyesight are able to see more than seven in near perfect conditions (my best friend says she sees fourteen!). When not viewed directly, though, the Pleiades have a strange glow about them, almost mist like. This is in no certain terms due to the large number of faint stars all concentrated into an area roughly four Moon diameters in size (around 2°). The truth is that there are many more than six or seven or fourteen stars in the Pleiades; there are, in fact, several hundred. With binoculars, it is easy to see as many as fifty, but you do not want to use too high a magnification to view this set of jewels. It is best viewed through binoculars or very low power (rich field) telescopes.
The brightest members of the Pleiades, and in fact most open clusters, are blue giants, massive, brilliantly burning stars that are very short lived. Because of their mass, they burn up most of their fuel in very little time, typically no more than a few tens of millions of years, and they go out as supernovae. Many of the stars within the Pleiades are not visible in binoculars, so the sheer number that actually make up this beautiful group remain hidden, only manifesting their presence telescopically or with larger aperture instruments.
As this small cluster moves along through space at a distance of over four hundred light years, it is passing through a cloud of dust. While not readily visible through binoculars (though possibly faintly visible to the naked eye using averted vision), this cloud adds to the beauty of the Pleiades when photographed, like splendid cirrus clouds floating amongst these fine stars.
(image courtesy Royal Observatory Edinburgh / David Malin)They Hyades themselves are actually very similar to the Pleiades though much older, on the order of half a billion years, and are more spread out as they have aged and drifted. Because of this fact, they are not as conspicuous a cluster, though a view through binoculars gives it away and shows its true nature. As with the Pleiades, there are many more faint members, giving a total of perhaps a couple hundred stars in total.
As impressive as the Pleiades but many times more distant lie two massive clusters, the famed Double Cluster in Perseus.
Lying several thousand light years away, the Double Cluster, like the Pleiades and the Hyades, is made up of blue supergiant stars; however, due to its distance, even on the most clear nights it appears as strictly two small fuzzy patches in the night sky, lying halfway between Cassiopeia and Perseus. While easy to find in binoculars, this twin cluster is best viewed telescopically, though even a modest telescope (as small as 50 mm) will bring it to life. Many astronomers feel that the two groups that make up the Double Cluster are actually gravitationally linked, that they actually influence each other and perhaps even share a common origin.
Also lying within the constellation of Perseus is a sight that surprised me the first time I saw it, a dazzling array of blue white stars sitting near Mirfak (Alpha Persei), the brightest star within Perseus. This is not a cluster but a stellar association, the Perseus III group.
Again, we're back to an object that is best viewed through binoculars. An association can best be thought of as a cluster that has matured, and like a family whose members have grown up, has begun to move apart, no longer influencing each other and their courses. The night sky actually has many associations; our Sun sits on the outskirts of a massive one, in fact. The only clue that gives away the presence of many associations is shared relative motion by member stars. Because of this, many associations are simply lost to the night. Luckily for us, the Perseus III group is distant enough to all share the same region of space when viewed from our Solar System. As viewed at 7x, the number of stars (around thirty can easily be made out under the right conditions) is startling, especially considering the proximity to other, apparently brighter (though actually much closer) stars.
The Solar System... In Ed Austin Regional Park
At my Freewebs site I've uploaded a page that shows a model of the Solar System built alongside Huffman Boulevard in Jacksonville's Southside. Looking to teach young people in various parts of our vast city, I've found myself looking at other parks and places to set up the same model, and Ed Austin Regional Park actually lends itself rather nicely. These Google Maps images (taken while improvements were still being made to the park) show how easy it is and how the contour of the park lends itself to the task. The Police Athletic League clubhouse actually sits on a rise in this former country club, and if you place our little 142 mm Sun near it, you can fit the entire inner system in the parking lot, while the two largest planets, Jupiter and Saturn, are near the periphery.
How about the rest of the Solar System? Yes, amazingly, you can even get Pluto (STILL a planet in my book!) to lie within the park!
Why is this an ideal setup, though? Basically, the Sun sits higher than many of the other locations I've chosen before. The advantage, simply put, is that the Sun remains readily visible down the entire model; if our little model Sun glowed, it would appear very much as it would from the actual planets themselves, appearing the same size when measured in angular size (though Pluto actually sits beyond a rise going into the park if you set it alongside the main road). While not a straight line (and again the images are a little misleading; the base images were taken during renovations and therefore not accurate), it does provide us with a useful model, one that has marked advantages over the original model laid out in Mandarin Park.
The Vagabond Astronomer will be at the Ed Austin Regional Park starting at 4:00 PM on the 8th of December, 2006, helping students build his model Solar System. Starting at 6:00 PM (after a picnic dinner), we'll move to the west end of the soccer field parking lot with a few telescopes to view those aforementioned clusters and anything else that might attract our attention. Hope to see you there!
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