A simple way to think of it would be if you lay a doughnut flat on a table and measure the thickness from the outside edge to the hole. Let's say it's 2 inches thick. Then measure the distance across the entire doughnut on the right and left edges without touching the hole. The amount of dough there may be 5 inches thick when seen edge on. The same principle works for a shell of gas. The shell of gas in a planetary nebula reflects more light from the edges because you are seeing more gas. The center seems hollow because you are looking through less gas. No matter where you look from, when you look right into the center you see less reflected light than around the edges so it looks like a ring.
Latitude is zero at every point on the equator.
yes.
I am not sure but on the move 2012 they said it was 3 million years....
Like EVERY naked-eye star AND virtually every star that can be resolved with anything short of world class optics, mu Cephei is a member of our Milky Way galaxy.
Pluto may be found about 40 astronomical units away from the star Sol. You could also say it is about 328 light minutes from Sol. Sol itself is in one of the spiral arms of the Milky Way galaxy, about 2/3rds from the center.
No. Nebulae exist in almost every galaxy.
Yes, unless it's a galaxy or nebula outside of the Milky Way... all the singular stars you can see are within our galaxy.
Planets> Pluto, Mercury Mars Venus, Earth, Neptune, Uranus, Saturn, Jupiter Stars> Sun, Sirius, Pollux, Arcturus, Aldebaren, Rigel, Pistol Star, Betelguese, Antares, V354 Cephei, VV Cephei A, VY Canis Majoris There are nebulas and galaxies. Nebulas> Homunculus Nebula, Sting Ray Nebula, Cat's Eye Nebula, Hourglass Nebula, Blinking Nebula, Ring Nebula, Boomerang Nebula, Horsehead Nebula, Bubble Nebula, Cone Nebula, Pillars Of Creation, Crab Nebula, Orion Nebula, Eagle Nebula, Great Nebula Of Carina, Rossete Nebula, Lagoon Nebula, Barnard's Loop, Tarentula Nebula Galaxies> Canis Major Dwarf Galaxy, Sagittarius Dwarf Galaxy, Small Magellanic Cloud, Large Magellanic Cloud, Sombrero Galaxy, Trianglum Galaxy, Milky Way Galaxy, Andromeda Galaxy, Cartwheel Galaxy, Pinwheel Galaxy, Whirlpool Galaxy, Tadpole Galaxy, NGC 4889, IC 1101, I don't really know the names of these> Abell 2029, Local Group, Virgo Cluster, Virgo Supercluster, Eridanus Supervoid, Pisces-Cetus, Supercluster Complex Diameter Of The Universe> At Least 150 Billion Light-Years
Every rotation of a planet on its axis is a planetary day.
Every galaxy interacts, via gravity, with every other galaxy.
No galaxy returns every 76 years. Halley's Comet, which is a comet, not a galaxy, becomes visible every 76 years.
The Milky Way (our galaxy) is believed to have one in the center. Every or almost every galaxy has a black hole in the middle of it.
There are white dwarfs in every galaxy.
No. Every star in the galaxy is a sun.
Every galaxy contains stars, if that's what you mean. "Galaxy" means "big bunch of stars". No stars ===> no galaxy.
Latitude is zero at every point on the equator.
You get every green star.