after it has fragmented from a interstellar gas cloud but before it has collapsed sufficiently for nuclear fusion reactions to begin. It may last from 100,000 to 10 million years, depending on the mass of the star. A protostar is surrounded by a dense cocoon of gas and dust that blocks visible light, but allows through large amounts of far infrared and microwave radiation. Protostars glow because of gravitational energy, as the matter collapses, it releases energy, making the star hot and glow.
This is not to scale! But it emphasizes this point: We are not unique! The Sun is one of billions of stars in our galaxy that is surrounded by planets, other, alien solar systems! Some like ours, some totally different.
Watch Pluto video
Comets are beautiful, and it is very cool when one passes by. They can look huge in the sky. How many people have seen a comet? Hale-Bopp perhaps? Does anyone remember Halleys in 1986? You can see why people were fascinated by them. Since ancient times, people have documented the coming of comets, and sometimes took them to be bad omens, because they didn’t know what they were. Can you imagine if something like this just appeared in the sky for a several weeks, and then went away? Must have been very confusing and scary.A modern photoFrom a Medieval TapestryFrom a Turkish AstronomerA Woodcarving from Amsterdam in the 1600s
Remember that the Sun is a G star. We know there are planets around G stars.
Could there be solar systems around red dwarfs?
Could there be solar systems around two stars, so when you look up in the sky you would see two Suns?
Up until 20 years ago, we could only guess. We could not do science yet, because we didn’t have the right technology. But that all changed very quickly, when astronomers began to be able to take extremely detailed spectra of stars. Spectra again, hmmm, they seem to be pretty important…