Originally, the word “nebula” referred to almost any extended astronomical object (other than planets and comets). The etymological root of “nebula” means “cloud”. As is usual in astronomy, the old terminology survives in modern usage in sometimes confusing ways. We sometimes use the word “nebula” to refer to galaxies, various types of star clusters and various kinds of interstellar dust/gas clouds. More strictly speaking, the word “nebula” should be reserved for gas and dust clouds and not for groups of stars.
By order in which they appear from top to bottom, left to right, here are the main types and some provided examples for visual reference:
Planetary Nebulae: Sh2-188
Planetary nebulae are shells of gas thrown out by some stars near the end of their lives. Our Sun will probably evolve a planetary nebula in about 5 billion years. They have nothing at all to do with planets; the terminology was invented because they often look a little like planets in small telescopes. A typical planetary nebula is less than one light-year across.
Dark Nebulae: LDN 1622
Dark nebulae are clouds of dust which are simply blocking the light from whatever is behind. They are physically very similar to reflection nebulae; they look different only because of the geometry of the light source, the cloud and the Earth. Dark nebulae are also often seen in conjunction with reflection and emission nebulae. A typical diffuse nebula is a few hundred light-years across.
Emission Nebulae: NGC 896
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 as they fall back into lower energy states (in much the same way as a neon light). These nebulae are usually red because the predominant emission line of hydrogen happens to be red (other colors are produced by other atoms, but hydrogen is by far the most abundant). Emission nebulae are usually the sites of recent and ongoing star formation.
Reflection Nebulae: NGC 1333
Reflection nebulae are clouds of dust which are simply reflecting the light of a nearby star or stars. Reflection nebulae are also usually sites of star formation. They are usually blue because the scattering is more efficient for blue light. Reflection nebulae and emission nebulae are often seen together and are sometimes both referred to as diffuse nebulae.
Woah technology is amazing (at National Museum of Scotland)
is masturbating while smoking weed called masturblazing
no its called highjacking
guys no it’s weedwhacking
no its called dissapointing ur mother
“The concept is simple. Take a blank sheet with nothing but the basic outline of a pinup girl and illustrate a unique scene around her.”
I’ll probably always reblog this cuz it’s just mind-blowing, holy cow
God we fuck up teenagers’ heads. We tell them that biological conditions are moral punishments and then we get all shocked when they don’t practice rational risk management of biological conditions. We teach them “sex is super desirable and all the cool kids do it, and it’s hideously shameful and will destroy your life” and we wonder why they act an eensy bit neurotic about it. If you tried to design a system for making sexually active kids confused and unsafe, you couldn’t do much better than the American media and school system.
And for once, the answer is relatively simple. Just talk about sex like it’s a part of life. Some people have sex and some people don’t, because people are different. STIs aren’t bad because they’re Dirty Crotch Rot; they’re bad because they’re contagious illnesses like strep throat or whooping cough, and you can ask a doctor to check for and treat them just like you would with strep throat. Unwanted pregnancy isn’t a scarlet A; it’s a mostly-preventable accident that sometimes occurs when people are going about their normal business of having sex. You can ask the school counselor about a variety of topics, including career planning, problems at home, questions about sex, or conflicts with teachers.
If we could just get the goddamn stick out of our collective ass and accept that sex is a human activity and teenagers are humans, maybe there wouldn’t be quite so many plaintive “I don’t understand my body and I’m confused and scared and I don’t know anyone I can ask in person” messages flying out into the world.
college should be $25
I want these. So bad.