Eagle Creek Observatory
"Teaching young minds about the heavens"

Deep Sky Objects

What are DSOs?
Basically, a Deep Sky Object is something other than a star, planet, asteroid, the Sun or the Moon. This leaves many, many different kinds of objects that are generally lumped into what are called "Nebulae." What are Nebulae? The word "nebulae" is plural of Nebula. Nebula comes from the Latin word for cloud or dust. This is exactly what you see when you look at most nebulae through all but the very largest telescopes. Nebulae include galaxies, globular clusters and gas clouds.
Galaxies are extremely large groupings of stars. These groupings may contain hundreds of billions of stars and are usually millions of lightyears away. The most distant object that can be seen with the unaided eye is the Great Andromida Galaxy. It is just over two million lightyears away.
Globular Clusters are large "balls" of stars that are in groups orbiting our galaxy. It is thought that each globular cluster has a large black hole at the center keeping the stars together with its gravity. Globular clusters are among the oldest structures associated with our galaxy. One of the brightest globular clusters is M13 in the constellation of Hercules.
Open Clusters are large groupings or "clumps" of stars in our galaxy. It is thought that the stars in each of these clusters formed from the same gas cloud. This is why they are so close together. There are several excellent open clusters, most can be viewed using binoculars and some are visible to the naked eye. M45 the Pleiades, is an excellent example of one of these "naked eye" open clusters. It can be found in the constellation Taurus and is often mistaken for the "Little Dipper".
Other examples of Open Clusters are
M6 "The Butterfly Cluster" in Scorpio
M44 "The Praesaepe" or "Beehive Cluster" in Cancer
Emission Nebula are areas of gas, mostly Hydrogen, that are illuminated by very hot, nearby stars. The Ultra-Violet light or X-Rays from these very hot stars causes the gas in the nebula to glow just like "Black Light" paint glows when exposed to Ultra-Violet light from a "Black Light".
In these nebula the Hydrogen glows red, Oxygen glows blue-green. The eye is not sensitive to color in very dim light so you won't see these colors through your telescope. Examples of Emission Nebula are"
M42 in the constellation of Orion.
One of my favorites in a small telescope is the M17 the Swan Nebula in the constellation of Sagittarius.

Planetary nebula are a type of Emission Nebula. They have nothing to do with planets. Why are they called "Planetary Nebula?" In the small, crude telescopes of Charles Messier's day these round nebula were mistaken for planets. If you look at some of these small round nebula with moderate sized backyard telescopes they do indeed look like planets. They are small disk-shaped objects usually having a blue-green color, although most will not have any color at all.
Planetary Nebula are caused by a star in its last stages of life blowing off its outer layers into a bubble. Usually what remains is the very small and very hot core. The core emits UV and X-Ray radiation causing the gasses in the bubble to be excited and glow.
Examples of Planetary Nebula are:
M27, the Dumbbell Nebula in the constellation of Vulpecula.
M57, the Ring Nebula in the constellation of Lyra.
M97, the Owl Nebula in the constellation of Ursa Major.
For more planetary nebula from STSCI click here.
Reflection Nebula are areas of gas and "dust" that are illuminated by nearby stars. The light from these stars reflects off of these areas of gas and dust to produce nebula that turn out mostly blue in color photographs. Examples of Reflection Nebula are"
M20 the Trifed Nebula, combination reflection and emission nebula in the constellation of Sagittarius.

Try your skill at a Messier Marathon!
Sorted by Messier Number or Sorted by RA

Below is a table of constellations containing various Deep Sky Objects brighter than about Magnitude 12

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Andromeda Antlia Apus Aquarius
Aquila Ara Aries Auriga
Bootes Caelum Camelopardalis Cancer
Canes Venatici Canis Major Capricornus Carina
Cassiopeia Centaurus Cepheus Cetus
Circinus Columbia Coma Berenices Corona Australis
Corvus Crater Crux Cygnus
Delphinus Dorado Draco Eridanus
Fornax Gemini Grus Hercules
Horologium Hydra Hydrus Indus
Lacerta Leo Leo Minor Lepus
Libra Lupus Lynx Lyra
Mensa Monoceros Musca Norma
Ophiucus Orion Pavo Pegasus
Perseus Phoenix Pisces Piscis Austrinus
Puppis Pyxis Reticulum Sagitta
Sagittarius Scorpius Sculptor Scutum
Serpens Sextans Taurus Telescopium
Triangulum Triangulum Australe Tucana Ursa Major
Ursa Minor Vela Virgo Volans