Asteroid is one.
astronomy
anatomical, anatomy,
Gas
A science letter that starts with A is ASTRONOMY!!
Zenith, zodiac, zodiacal light.
Flares is a space word. It begins with the letter f.
· orbit · ozone, maybe Orion Oort cloud
any anatomy astrology astronomy allegory allegedly advisably
X-ray star, and X-ray astronomy :)
Astronomy is the study of the stars and galaxies. To start learning about astronomy take a college class or check out books from your local library.
There are lots of such words. I suggest you either read an introductory article on Astronomy, for example on Wikipedia; or do a Google search for "Astronomy glossary".
Some words do not have opposites. Astronomy is one of them.