The Universe

THE UNIVERSE The universe is commonly defined as the totality of everything that exists, including all physical matter and energy, the planets, stars, galaxies, and the contents of intergalactic spaceexists

CONSTELLATION a constellation is a group of celestial bodies, usually stars, which appear to form a pattern in the sky.

STARS A star is a massive, luminous ball of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible from Earth during the night when they are not outshone by the Sun or blocked by atmospheric phenomena. Historically, the most prominent stars on the celestial sphere were grouped together into constellations and asterisms, and the brightest stars gained proper namesplasmagravitydegenerate matterEarthSunenergycelestial sphereconstellationsasterisms

ASTEROID Are a class of small Solar System bodies in orbit around the Sun. Any of numerous small celestial bodies that revolve around the sun, with orbits lying chiefly between Mars and Jupiter and characteristic diameters between a few and several hundred kilometers. Also called minor planet, planetoid.small Solar System bodiesSun

COMET A celestial body, observed only in that part of its orbit that is relatively close to the sun, having a head consisting of a solid nucleus surrounded by a nebulous coma up to 2.4 million kilometers (1.5 million miles) in diameter and an elongated curved vapor tail arising from the coma when sufficiently close to the sun. Comets are thought to consist chiefly of ammonia, methane, carbon dioxide, and water.

METEORITE A meteorite is a natural object originating in outer space that survives an impact with the Earth's surface. A meteoroid is a sand to boulder sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's (or another body's) atmosphere is called a meteor.

SATELLITE A celestial body that orbits a planet; a moon.

THE MOON The Moon is the only natural satellite of Earth. The moon is a cold, dry orb whose surface is studded with craters and strewn with rocks and dust. The moon has no atmosphere. Recent lunar missions indicate that there might be some frozen ice at the poles. Earthfrozen ice at the poles

The Moon.

GALAXY Any of numerous large-scale aggregates of stars, gas, and dust that constitute the universe, containing an average of 100 billion (10 11 ) solar masses and ranging in diameter from 1,500 to 300,000 light- years. Also called nebula.

THE MILKY WAY Milky Way Galaxy, commonly referred to as just the Milky Way, or sometimes simply as the Galaxy, is the galaxy in which the Solar System is located. The Milky Way is a barred spiral galaxy that is part of the Local Group of galaxies. It is one of hundreds of billions of galaxies in the observable universe.galaxySolar Systembarred spiral galaxyLocal Groupobservable universe

The Milky Way

THE SOLAR SYSTEM Our solar neighborhood is an exciting place. The Solar System is full of planets, moons, asteroids, comets, minor planets, and many other exciting objects.

The Solar System Our solar system consists of an average star we call the Sun, the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. It includes: the satellites of the planets; numerous comets, asteroids, and meteoroids; and the interplanetary medium. The Sun is the richest source of electromagnetic energy (mostly in the form of heat and light) in the solar system. The whole solar system, together with the local stars visible on a clear night, orbits the center of our home galaxy, a spiral disk of 200 billion stars we call the Milky Way. The Milky Way has two small galaxies orbiting it nearby, which are visible from the southern hemisphere. The nearest large galaxy is the Andromeda Galaxy. It is a spiral galaxy like the Milky Way but is 4 times as massive and is 2 million light years away. Our galaxy, one of billions of galaxies known, is traveling through intergalactic space.Sun MercuryVenusEarthMarsJupiterSaturnUranusNeptunePlutocometsasteroidsMilky WayAndromeda Galaxy