These are glowing clouds of gas and dust residing in the spiral arms of our own Milky Way Galaxy. These are typically very colorful objects but the vivid colors are only seen in CCD images or astrophotography. Using a 250mm (10”) or larger telescope in a rural location, you can begin to see some faint color on some of the nebulae and in smaller telescopes you will see very faint gray or greenish smudges. You can begin to see some faint structure with 100mm (4”) and larger telescopes.
There are two main types of nebulae – (1) planetary nebulae which are relatively small ball-shaped clouds of expanding gases with faint central stars which are believed to be the remnants of stellar explosions, and (2) diffuse nebulae which are vast, irregularly-shaped clouds of gas and dust.
Nebulae are also described as emission (shine brightly) or reflection (do not shine).
These are vast, remote “island universes”, each composed of many billions of stars. Galaxies are beyond the boundaries of our own Milky Way Galaxy and are millions of light years away. Galaxies exist in a variety of sizes with regular and irregular shapes.
They are very difficult to observe due to their faintness and the distances. It is possible in a rural area to discern hints of structure on the brightest galaxies with 100mm (4”) to 150mm (6”) apertures and more structure becomes visible as the aperture increases.
Galaxies are classified as (1) spiral – these feature a central bump or budge of old stars surrounded by spiral arms containing younger stars, (2) barred-spiral – these have an obvious central “bar” of material, (3) elliptical – these are armless masses of old stars, and (4) irregular – these show no symmetry, exhibiting odd or chaotic structure.
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