A light year is the distance light travels in one year -- about 5.88 trillion miles (9.5 trillion km).

Thallophytes (like algae) are plants that have no stem, roots or leaves.

Concave or hollow objects have centers of mass inside their "shells", so the center of mass of a Frisbee will not lie inside the object, but rather outside towards the curved surface.

If a body covers a displacement of 50 meters in 10 seconds, it is traveling at a velocity of 5 meters per second.

A hydrogen atom (H) contains one electron and H+ represents a hydrogen ion, which means it has lost its only electron.

Metals are not permeable because they don't allow liquids and gases to pass through them.

Computer models show that not only is Jupiter's ocean (made of liquid hydrogen) the largest in the solar system, but that it is about 25,000 miles (40,000 km) deep -- roughly as deep as the Earth is around!

Unexpected changes in the orbit of Mercury helped confirm Einstein's theory of general relativity: The orbit of Mercury is shifting very gradually over time, due to the curvature of space-time around the massive sun. In a few billion years, it could even collide with Earth.

It does rain in Venus's atmosphere, but the rain evaporates 25 kilometers above the surface, so none gets to the surface.

On July 29, 2005, astronomers at Caltech announced the discovery of a new trans-Neptunian object, Eris, which was believed at the time to be bigger than Pluto. This led the International Astronomical Union to define the term "planet" formally in 2006, during their 26th General Assembly. That definition excluded Pluto and reclassified it as a dwarf planet.