What is gravity? - NASA
Newton's "law" of gravity is a mathematical description of the way bodies are observed to attract one another, based on many scientific experiments and observations. The gravitational equation says that the force of gravity is proportional to the product of the two masses (m 1 and m 2 ), and inversely proportional to the square of the distance ...
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: 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: Galaxies - NASA
A galaxy is a cluster of stars, dust, and gas which is held together by gravity. Galaxies are scattered throughout the universe and they vary greatly in size. A galaxy may be alone or it may be in a large group of galaxies called a "supercluster". Galaxies are classified by scientists according to their shape and appearance.
StarChild: Stars - NASA
The last of the hydrogen gas in the outer shell is blown away to form a ring around the core. This ring is called a planetary nebula. When the last of the helium atoms in the core are fused into carbon atoms, the medium size star begins to die. Gravity causes the last of the star's matter to collapse inward and compact.
Gravity/Gravitational Field | NASA Earthdata
Gravity/Gravitational Field Dealing with the determination of the size and shape of the earth, the Earth's gravitational field, and the location of points fixed to the Earth's crust in an Earth-referred coordinate system.
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StarChild: Glossary - NASA
An invisible object in outer space formed when a massive star collapses from its own gravity. A black hole has such a strong pull of gravity that not even light can escape from it. BLUR To make less clear, to run together. BIG BANG THEORY A theory that says the universe began with a super-powerful explosion. BOLT A flash of lightning. BOULDER
StarChild: Galaxies - NASA
A galaxy contains stars, gas, and dust which are held together as a group by gravity. There may be millions, or even billions, of stars in one galaxy. There are billions of galaxies in the universe. Galaxies are labeled according to their shape. Some galaxies are called "spiral", because they look like giant pinwheels in the sky.
How do we know that dark matter exists? - NASA
The cluster does not behave as scientists would expect it to if only the visible matter is generating the gravity present in the cluster. 'Dark matter' theory suggests that a huge amount of dark (invisible to direct observation) matter, interacting gravitationally with the normal, visible matter in the universe, exists.