What is gravity? - NASA
Gravity is a force of attraction that exists between any two masses, any two bodies, any two particles. Gravity is not just the attraction between objects and the Earth. It is an attraction that exists between all objects, everywhere in the universe. Sir Isaac Newton (1642 -- 1727) discovered that a force is required to change the speed or ...
Teachers' Center Activity: Gravity Effects on Planet Motion - NASA
Gravity and Its Effect on Planetary Orbits 1. Introduction: Review the definition of gravity; Drop a ball and explain why it falls downward; Explain that the strength of a gravitational pull is determined by the masses of the objects involved and the distance between the objects
StarChild: Dark Matter - NASA
Dark matter is composed of particles that do not absorb, reflect, or emit light, so they cannot be detected by observing electromagnetic radiation. Dark matter is material that cannot be seen directly. We know that dark matter exists because of the effect it has on objects that we can observe directly. Scientists study dark matter by looking at ...
StarChild: Glossary - NASA
A cluster of stars, dust, and gas held together by gravity. GAMMA-RAYS Penetrating short wave electromagnetic radiation of very high frequency. GEOSYNCHRONOUS An orbit in which a satellite's rate of revolution matches the Earth's rate of rotation. This allows the satellite to stay over the same site on the Earth's surface at all times.
StarChild: Stars - NASA
A star is a brilliantly glowing sphere of hot gas whose energy is produced by an internal nuclear fusion process. Stars are contained in galaxies. A galaxy contains not only stars, but clouds of gas and dust. These clouds are called nebulae, and it is in a nebula where stars are born. In the nebula is hydrogen gas which is pulled together by ...
StarChild: The Planets and Dwarf Planets - NASA
The Planets and Dwarf Planets. A planet is a large space body which reflects the light of a star around which it . The planets in our are classified as inner planets and outer planets. The inner planets, the closest to the Sun, are solid spheres of rock and include Mercury, Venus, Earth, and Mars. The inner planets were constantly bombarded by ...
What is a brown dwarf? - NASA
In other words, a planet is not hot enough or heavy enough to produce its own light. Brown dwarfs are objects which have a size between that of a giant planet like Jupiter and that of a small star. In fact, most astronomers would classify any object with between 15 times the mass of Jupiter and 75 times the mass of Jupiter to be a brown dwarf.
StarChild: The Asteroid Belt - NASA
The Asteroid Belt. Asteroids are often referred to as minor planets or planetoids. An asteroid is a rocky body in space which may be only a few hundred feet wide or it may be several hundred miles wide. They are considered to be debris left over from the formation of the solar system. Many asteroids orbit the Sun in a region between Mars and ...
What is a light-year and how is it used?? - NASA
Question: What is a light-year and how is it used? Answer: A light-year is a unit of distance. It is the distance that light can travel in one year. Light moves at a velocity of about 300,000 kilometers (km) each second. So in one year, it can travel about 10 trillion km. More p recisely, one light-year is equal to 9,500,000,000,000 kilometers ...
Where did the Moon come from? - NASA
The Capture Theory: This theory proposes that the Moon was formed somewhere else in the solar system, and was later captured by the gravitational field of the Earth. The Moon's different chemical composition could be explained if it formed elsewhere in the solar system, however, capture into the Moon's present orbit is very improbable.