Speed of light
Hubble Space Telescope
Big bang theory
Specialty of Professor Carl Sagan
Specialty of Professor Stephen Hawking
The most common type of galaxy in the universe is the elliptical galaxy, but the Milky Way is a spiral galaxy.
Elliptical galaxies are spherical or ellipse-shaped. The Milky Way is flattened and has spiral arms.
Most (but not all) elliptical galaxies are dwarfs that contain fewer than one million stars; the Milky Way and most spiral galaxies are large. The Milky Way contains about 400 billion stars.
The Milky Way is the only galaxy scientists know of that has living organisms.
The Milky Way is smaller than most elliptical galaxies.
Scientists know that the dark matter and dark energy absorb all light in the visible spectrum, which means they are black in color.
Dark matter and dark energy cannot be seen or detected directly (only indirectly).
The existence of dark matter and dark energy is inferred from observed effects -- not by seeing them.