General readers; undergraduates; technical program students. Current promotions. Viewing the Constellations with Binoculars. More Info. Budget Astrophotography. Astronomical Sketching. The Night Sky Companion.
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Deep Sky Objects
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Ecology and Conservation of Birds in Urban Environments. Rewilding European Landscapes. Bats in the Anthropocene. Integrated Assessment of Running Waters in Europe. One of the tricks to successful deep sky observing is to choose targets that are appropriate for your telescope. The Wild Duck cluster M11 is always worth a look in any telescope. The Beehive is best in smaller instruments. NGC is best in larger instruments.
Why are stars in clusters? Stars form from giant collections of gas clouds in space when some sort of shock wave passes through, compressing the clouds such that they begin to collapse and form stars. Unlike people, stars are formed all together in this way. Over time these stars may wander away from each other, but depending on many factors, for a time they stay together in a group.
The giant gas clouds where stars form are concentrated in the plane of our galaxy -- along the Milky Way, so this is also where most open clusters are found. Globular Clusters These star clusters are much larger groupings of stars that are drawn together into a much more concentrated, spherical shape than the open clusters. Globular clusters typically have hundreds of thousands of stars all packed into a tight ball.
Except perhaps for Saturn's rings, there may be no view more breathtaking than the myriad stars of a globular filling your field of view.
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Stick to the brighter globulars for the most stunning views. Large aperture instruments will resolve the smaller, fainter globulars; they make good targets for these scopes when you get tired of looking at just the bright ones. Globular star clusters are composed of old stars.
Unlike the open clusters, which form continuously, all the globulars formed very long ago. It appears that globular clusters form when two galaxies collide; such a collision stimulates star formation on much larger scales. The globular clusters of our galaxy are all approximately the same age; perhaps formed when our galaxy collided with another long ago. They are found outside of the disk of or galaxy, forming a large spherical cloud of clusters about the galactic center.
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That's why most globulars are visible in northern hemisphere summer when sagittarius is in view. The center of our galaxy is in this direction. Diffuse Nebulae Diffuse Nebulae pronounced nebulee are clouds of glowing gas and dust. Our galaxy is filled with these clouds, which lie mostly along the Milky Way. Most of this gas is dark, but when a bright, hot star is nearby it can glow.
Deep Sky Objects – Derekscope
There are two ways for the gas to glow. Both ways require lots of blue and UV light entering the nebula. Massive, hot stars are a excellent source of such light. It is these nebulae that cause the most disappointment for beginners expecting to see the vivid detail and colors found in long exposure photographs. Your eye simply can't see color and faint detail as well as a camera can. So in most cases these nebulae appear as faint, hazy patches of sky.
This nebula may appear as a hazy patch even to the naked eye. In all but the tiniest of telescopes it forms a beautiful twisting, swirling mass of clouds, usually a pale gray or slight green color. There are some people who claim to see a tinge of pale red as well. Another good example is the Swan. The light from a star becomes scattered as it passes through the a gas cloud, in much the same way that sunlight is scattered by our atmosphere. It is the dust particles in the cloud that do the scattering. The blue light is scattered more easily, so the other colors tend to pass right on through.
The blue light, however, gets scattered in all directions. So, if you stand off to the side and look at the cloud, it appears to glow blue from the light being scattered in your direction. Astronomers call this a reflection nebula. They appear distinctly blue in photographs, but appear only as a hazy gray in a telescope.
The other way for a cloud to glow is when the light from the star is absorbed by the gas atoms and then remitted. Hydrogen gas atoms like to absorb UV light. When they do their only electron uses that energy to break free of the atom and go flying off.
Related Guide to Observing Deep-sky Objects
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