Novas

Space is mostly made up of vacuum, which is space devoid of matter. However, space does contain small amounts of particles such as atoms, cosmic dust, and radiation. These particles are spread out across vast distances in space.

A pulsar is a type of neutron star, a collapsed core of an extremely massive star that exploded in a supernova. Whereas white dwarfs have incredibly high densities by earthly standards, neutron stars are even denser, cramming roughly 1.3 solar masses into a city-sized sphere.

Our common terms for distance, miles and kilometers, are useful enough to measure distances around town, and even around the country. But for distances beyond our solar system, it's cumbersome to carry around a bushel-basket full of zeroes to add to the distance measurements.

So we typically phrase things in terms of "light-years", the distance that light would travel on one year. Light moves at 186,000 miles or 300,000 kilometers per SECOND, so a light year is quite a distance; 186000 * 60 * 60 * 24 * 365.24 miles, which is 5,869,552,900,000 miles. The nearest star, Proxima Centauri, is four times FURTHER away at 4.2 light-years, so you can see that the distances to even the nearer stars are quite cumbersome when expressed in conventional units.

In metric terms, we have, perhaps, another way to go. The standard distance is the "meter", and latinate prefixes are used to denote larger quantities, such as the kilo-meter, for 1,000 meters; about 6-tenths of a mile.

In computer terms, the word "byte" is used to designate the storage space required to store one ASCII character. A "kilo-byte" is a thousand bytes (actually, 1024 bytes, but close) and a "megabyte" is a million (plus a bit) bytes. A gigabyte is a billion, and a terabyte is a trillion.

So, let's extend that to astronomy. One light year is 5.8 tera-miles.

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Yes!!

An extremely dense dying star is called a neutron star. It is formed when a massive star collapses in a supernova explosion, leaving behind a core made mostly of neutrons. Neutron stars are incredibly dense, packing the mass of the sun into a sphere only about 12 miles in diameter.

Supernova. There are Chinese and European accounts from centuries ago of "guest stars," new stars that appeared and faded from view. We can see the expanding remnants of those supernova today--one is the Crab Nebula.

Light Speed. 186,000 mps