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Open Clusters
Open clusters are loose clumps of dozens or hundreds of young stars. They are generally not bound by gravity and will disappear in a relatively short period of time. They are often with more diffuse nebula-like stars as well. They are also called "galactic clusters" because they are usually found in the plane of the galaxy. A usual open cluster is less than 50 light years across. -
Globular Clusters
Globular clusters are groups of many thousands (sometimes as many as a million!) of stars stuck in one place by gravity. They usually have very old stars. Globular clusters are not only in one place of the galaxy but rather are random throughout the Halo (The edge of the galaxy.) There are several hundred globular clusters in our galaxy! A usual globular cluster is a few hundred light years across! -
Planetary Nebulae
Planetary nebulae are shells of gas (not that kind of gas!) thrown out by some stars near the end of their lives. Our Sun will probably produce a planetary nebula in about 5 billion years! They have nothing at all to do with planets. The term was invented because they often look a little like planets in small telescopes. A usual planetary nebula is less than one light year across! -
Dark Nebulae
Dark nebulae are clouds of dust which are just blocking the light from whatever is behind. They are very similar to reflection nebulae, they look different only because of the size and shape of the light source, the cloud and the Earth. Dark nebulae are also often seen joining with reflection and emission nebulae. I inferred to find this date, and I inferred this date because they are often seen with reflection nebulae which was discovered in 1834. -
Reflection Nebulae
Reflection nebulae are clouds of dust which are just reflecting the light of a nearby star or stars. They are also usually sites of star formation. They are usually blue because the scattering is better for blue light. Reflection nebulae and emission nebulae are often seen together and are sometimes both called diffuse nebulae. -
Emission Nebulae
Emission nebulae are clouds of high temperature gas. The atoms in the cloud are energized by ultraviolet light from a nearby star and emit radiation. These nebulae are usually red because the huge amount of hydrogen happens to be red (other colors are produced by other atoms, but hydrogen is by far the most common). I inferred to find the date, the reason I chose this date is because they are often seen with reflection nebulae, which were discovered in 1834. -
Supernova Remnants
Supernovae happen when a massive star ends its life by EXPLODING! (When I die, I want to explode as well.) For a few days a supernova emits as much gas, stardust and energy as a whole galaxy! (How?!) When it's all over, a big part of the star is blown into space as a supernova remnant. A usual supernova remnant is at most few light years across!
