Placidus
05-05-2015, 01:37 PM
Full moon. Need something bright. We chose open cluster NGC 3766 because it was a good size, up all night, far from the moon, and had at least two red giants to add interest.
Every picture tells a story:
By far the most common stars in the galaxy are red dwarfs - small dim cool stars that outnumber the sun by thousands to one. The background in this image is awash with these little red dots.
But the stars visible to the naked eye are mostly white or blue-white: ultra-rare stars that just happen to be tens of thousands of times brighter than the sun, and therefore conspicuous.
Here we have an open cluster, a young agglomeration of at least 200 of these super-rare blue-white stars (we got bored counting). They are blue-white, not blue, and we've tried to be subtle and semi-realistic with the colour.
At least two of them have run out of hydrogen in their core, and the core, losing thermal energy, has shrunk, liberating even more gravitational energy. Eventually the core has become hot enough to ignite helium. The resultant nuclear energy release has caused the outer envelope of the star to swell, producing a red giant. Thus we see two beautiful orange stars in the image. Hugely swollen, with an enormous surface area (say a sphere out to the orbit of Mars in size) and consequently radiating prodigiously bright, losing heat, thence cool, and thus orange. There are other orange stars in the image, but much fainter, and perhaps not part of the cluster.
Since only two out of 200 of these already very rare OB stars have entered the ascending giant branch, we can see from the image that red giants are especially rare. They are very short-lived. Since the parent stars are large, they will probably end their lives as type II supernovae.
RGB 2 hours each in 5 min subs. Aspen CG16M on 20" PlaneWave.
Guiding was a breeeze: guiding independently on some 50 of the 200 stars in the cluster, our RMS guiding error was only 0.2 sec arc.
Field 26 min arc.
Big one here
(http://www.mikeberthonjones.smugmug.com/Category/Clusters/i-FTSLRpJ/0/O/NGC%203766%20Centaurus.jpg)
Best,
Mike and Trish
Every picture tells a story:
By far the most common stars in the galaxy are red dwarfs - small dim cool stars that outnumber the sun by thousands to one. The background in this image is awash with these little red dots.
But the stars visible to the naked eye are mostly white or blue-white: ultra-rare stars that just happen to be tens of thousands of times brighter than the sun, and therefore conspicuous.
Here we have an open cluster, a young agglomeration of at least 200 of these super-rare blue-white stars (we got bored counting). They are blue-white, not blue, and we've tried to be subtle and semi-realistic with the colour.
At least two of them have run out of hydrogen in their core, and the core, losing thermal energy, has shrunk, liberating even more gravitational energy. Eventually the core has become hot enough to ignite helium. The resultant nuclear energy release has caused the outer envelope of the star to swell, producing a red giant. Thus we see two beautiful orange stars in the image. Hugely swollen, with an enormous surface area (say a sphere out to the orbit of Mars in size) and consequently radiating prodigiously bright, losing heat, thence cool, and thus orange. There are other orange stars in the image, but much fainter, and perhaps not part of the cluster.
Since only two out of 200 of these already very rare OB stars have entered the ascending giant branch, we can see from the image that red giants are especially rare. They are very short-lived. Since the parent stars are large, they will probably end their lives as type II supernovae.
RGB 2 hours each in 5 min subs. Aspen CG16M on 20" PlaneWave.
Guiding was a breeeze: guiding independently on some 50 of the 200 stars in the cluster, our RMS guiding error was only 0.2 sec arc.
Field 26 min arc.
Big one here
(http://www.mikeberthonjones.smugmug.com/Category/Clusters/i-FTSLRpJ/0/O/NGC%203766%20Centaurus.jpg)
Best,
Mike and Trish