What are shark skeletons made of, instead of bone?

What famous catalog of deep-sky objects, compiled by a French astronomer in the 1700s, contains 110 entries?

What type of coral does not rely on photosynthetic algae and must be fed directly?

The red supergiant UY Scuti is one of the largest known stars. By current estimates, its radius is roughly how many times the Sun's?

What phenomenon causes stars to appear to twinkle when viewed from Earth's surface?

What type of filtration uses live rock and sand beds to naturally process waste in a marine aquarium?

What is the nitrogen cycle process called that must occur before adding fish to a new saltwater tank?