Physical Geography

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Mars is the fourth planet from the Sun and the second smallest planet in the Solar System. Named after the Roman god of war, it is often described as the “Red Planet”, as the iron oxide prevalent on its surface gives it a reddish appearance.

A nebula is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, nebula was a name for any extended astronomical object, including galaxies beyond the Milky Way.

Because it is “tidally-locked” to the Earth. The Earth’s gravity slows down the moon’s rotation, so that it rotates at the same speed as it revolves around the Earth. Imagine a person who walks around a center pole, but shifts their body so they are always facing it as they walk.

Jupiter's radius is about 1/10 the radius of the Sun, and its mass is 0.001 times the mass of the Sun. Jupiter's mass is 2.5 times that of all the other planets in the Solar System combined—this is so massive that its barycenter with the Sun lies above the Sun's surface at 1.068 solar radii from the Sun's center.

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Venus is often called the Earth's sister planet. The Earth and Venus are very similar in size with only a 638 km difference in diameter, Venus having 81.5% of the Earth's mass.

Being the largest planet of solar system, its mass is one thousandth of the mass of the Sun. Jupiter, the giant among giants, has enough mass to make 318 Earths. Its diameter is about 11 times that of Earth (and about one tenth that of the Sun).

Jupiter is the fastest spinning planet in our Solar System rotating on average once in just under 10 hours. That is very fast especially considering how large Jupiter is. This means that Jupiter has the shortest days of all the planets in the Solar System.

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The Moon's atmosphere is negligibly thin, essentially vacuum, so its sky is always black, as in the case of Mercury. However, the Sun is so bright that it is impossible to see stars during the daytime, unless the observer is well shielded from sunlight (direct or reflected from the ground).

Light travels through space at just over 186,000 miles per second. The moon is just under 250,000 miles from Earth, so light from the Moon's surface has to travel more than one second (about 1.3 seconds) to reach us.

Comets go around the Sun in a highly elliptical orbit. They can spend hundreds and thousands of years out in the depths of the solar system before they return to Sun at their perihelion. Like all orbiting bodies, comets follow Kepler's Laws - the closer they are to the Sun, the faster they move.

The planets are kept in motion in their respective orbits by Gravitation and centrifugal force. The Sun's gravity pulls on the planets, just as Earth's gravity pulls down anything that is not held up by some other force and keeps you and me on the ground.

Ursa Major is a constellation in the northern sky, whose associated mythology likely dates back into prehistory. Its latin name means "greater she-bear", standing as a reference to and in direct contrast with nearby Ursa Minor, the lesser bear.