What is the Universe?

• The universe is all of space and time and its contents, including planets, stars, galaxies, and all other forms of matter and energy.

• The Big Bang Theory is the prevailing cosmological description of the development of the universe.

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How big is the Universe?

• The universe is considered to be infinite.

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What are the main components of the Universe?

• The main components of the Universe are: Galaxies, Nebulae, Stars, Planets, Satellites/Moons, Asteroids, Meteors, and Comets.

What are the biggest parts of the Universe?

• Galaxies

• A galaxy is a gravitationally bound system of stars, nebulae, stellar remnants, interstellar gas, dust, and dark matter.

Are there different types of galaxies?

• The three main types of galaxies are Spiral, Elliptical and Irregular.

• There are also Barred Spiral, Peculiar, and Lenticular

• We live in the spiral galaxy called the Milky Way

What are the largest components of galaxies?

• Nebulae

• A nebula is an interstellar cloud of dust, hydrogen, helium, and other ionized gases, visible in the night sky either as an indistinct bright patch or as a dark silhouette against other luminous matter

What is a Star?

• A star is a large celestial body made of mostly hydrogen and helium gases that emits light due to nuclear (fusion) reactions.

• What is the star closest to the Earth?

• The nearest star to Earth is the Sun.

What is a planet?

• A planet is a celestial body that (a) is in orbit around a star, (b) (nearly round) shape, and (c) has cleared the neighborhood around its orbit.

What is a moon or natural satellite?

• In a generic sense, a moon is a natural satellite that orbits a planet.

• In a specific sense, the Moon is the only natural satellite of Earth and the fifth largest such object. It is the brightest object in the Earth's sky after the Sun.

What are asteroids?

• An asteroid is a small irregualar rocky body orbiting the sun.

• Large numbers of these, ranging in size from nearly 600 miles (1,000 km) across (Ceres) to dust particles, are found (as the asteroid belt ) especially between the orbits of Mars and Jupiter, though some have more eccentric orbits, and a few pass close to the earth or enter the atmosphere as meteors

What is a meteroid?

• A meteoroid is a small body moving in the solar system that would become a meteor if it entered the earth's atmosphere.

• What is a meteor?

• A meteor is a small body of matter from outer space that enters the earth's atmosphere, becoming incandescent as a result of friction and appearing as a streak of light.

What is a comet?

• A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing.

• This produces a visible atmosphere or coma, and sometimes also a tail.