Until 2006 Pluto was classified as the ninth planet. At that time, it was declassified as a planet and reclassified as a "dwarf planet."

Neptune is the eighth planet in our solar system. Titan and Ganymede are moods of Saturn and Jupiter, respectively.

Until 2006 Pluto was classified as the ninth planet. At that time, it was declassified as a planet and reclassified as a "dwarf planet."

Neptune is the eighth planet in our solar system. Titan and Ganymede are moods of Saturn and Jupiter, respectively.

Until 2006 Pluto was classified as the ninth planet. At that time, it was declassified as a planet and reclassified as a "dwarf planet."

Neptune is the eighth planet in our solar system. Titan and Ganymede are moods of Saturn and Jupiter, respectively.

Helium is frequently used in balloons at parties. It is lighter in mass than the surrounding air, allowing it to "float" upwards. As a noble gas, helium is also largely inert and has numerous practical purposes in chemistry due to this property.

Beginning in 2013, the amount of helium used began to far exceed the supply, resulting in a helium shortage.

Neon and argon are noble gases (like helium). Hydrogen is not a noble gas, and is actually highly reactive.

Helium is frequently used in balloons at parties. It is lighter in mass than the surrounding air, allowing it to "float" upwards. As a noble gas, helium is also largely inert and has numerous practical purposes in chemistry due to this property.

Beginning in 2013, the amount of helium used began to far exceed the supply, resulting in a helium shortage.

Neon and argon are noble gases (like helium). Hydrogen is not a noble gas, and is actually highly reactive.

Helium is frequently used in balloons at parties. It is lighter in mass than the surrounding air, allowing it to "float" upwards. As a noble gas, helium is also largely inert and has numerous practical purposes in chemistry due to this property.

Beginning in 2013, the amount of helium used began to far exceed the supply, resulting in a helium shortage.

Neon and argon are noble gases (like helium). Hydrogen is not a noble gas, and is actually highly reactive.

The universe was thought to begin because of the Big Bang, which occurred around 14 billion years ago.

The universe was thought to begin because of the Big Bang, which occurred around 14 billion years ago.

The universe was thought to begin because of the Big Bang, which occurred around 14 billion years ago.

The air in the atmosphere is largely composed of nitrogen and oxygen. Nitrogen represents the largest contributor, composing approximately 79% of the earth's atmosphere. Oxygen represents about 20% of the earth's atmosphere. Other gases, such as hydrogen, carbon dioxide, and methane, comprise less than 1% of the atmosphere.