William Parsons was the first astronomer to show that spiral nebulae have large Doppler shifts.
What are Spiral nebulae?
- In space, a nebula is a huge cloud of gas and dust. Some nebulae, including multiple nebulae, are made of gas and dust that have been released from the explosion of a dead star called a supernova. There are other nebulae that are star-forming regions.
- Edwin Hubble began observing Cepheid variables in many spiral nebulae, including the alleged Andromeda Nebula, in 1923, demonstrating that they are, in fact, full-fledged galaxies outside our own. Since then, the phrase spiral nebula has lost favor.
- One group of astronomers believed that spiral nebulae were parts of our Milky Way galaxy, whereas the other group believed that these objects were actual galaxies that were outside of the Milky Way galaxy.
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