Before telescopes were invented in the early 1600s, most of what we now know exists in outer space was completely unimagined and largely unimaginable by ordinary human beings (like us). Galileo observed bizarre and shocking things – spots on the sun, planetlings orbiting Jupiter, countless stars never seen before – that exploded ideas in the old cosmological philosophies.

Certain fuzzy washes of light – a handful of which (like the great galaxy in the constellation Andromeda) can be seen by the unaided eye – were revealed in telescopes to exist by the dozens, and more. For decades it was generally assumed that the washes of light were all of the same ilk, although what that ilk was, was unknown. By the mid-1700s telescopes had improved, more starlight was charted, and new ideas about the structure of the cosmos were formulating out of the old. Many wild notions about the fuzzy patches eventually condensed into two basic theories: the “nebular hypothesis” and the “island universe” hypothesis.

The Latin word “nebula” means “cloud,” and the nebular hypothesis was that the fuzzy patches were distant clouds of gas slowly coalescing into planets. The French mathematician Pierre-Simon LaPlace suggested that our own sun and planets had formed this way. Even more spectacular was the idea proposed by the mighty Enlightenment philosopher Immanuel Kant, that the clouds were extremely distant island universes – collections of stars beyond our own collection, the Milky Way galaxy.

It turned out both, overall, were right. There are extragalactic galaxies, and there are several kinds of nebulae. Two hundred and some years later it’s a generally accepted fact of astronomy that so many galaxies exist, so far away, that their number is essentially unknowable. Galaxy M31 in Andromeda is an island in outer space of possibly a trillion stars about 2.2 million light-years away.

The nebulae seen in telescopes are inside our own galaxy. A nebula, as astronomers use the word, is a cloud of gas and dust floating near stars. Four basic kinds are detected in telescopes: reflection, emission, dark and planetary. A reflection nebula reflects visible light from nearby stars strongly enough for telescopes to pick up. An emission nebula glows with heat, or energy, detected by telescopes that pick up light in wavelengths the human eye can’t see (which is most of the light there is).

A dark, or absorption, nebula is a cloud of gas and dust that neither reflects light nor emits heat, but instead is seen as a silhouette against a background of star or nebula light. A dark nebula familiar in Hubble Space Telescope pictures is the Horsehead Nebula.

A planetary nebula is a shell of gas surrounding an old star. It does not actually involve planets – the phrase is a linguistic fragment left over from the ideas of philosophers like LaPlace and Kant.

It is theorized that stars are created when dust and gas condense over immensely long periods of time, and that planets coalesce from the disks of material left over from star formation. At the end of their lives, some stars explode into gas, dust and energy. New stars reformulate out of the material from the old exploded stars.

What a star explosion or a star birth is actually like, is unimaginable by ordinary beings like us. There are more things in heaven and Earth than are verified in our astronomy.