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the scientific study of the universe.


the time required for the earth to orbit once around the sun.


roughly the time required for the moon to orbit once around Earth.


the time required for Earth to rotate once on its axis.

Ptolemaic theory

belief that earth is the center of the universe


thought that the sun was the center of the universe and that Earth and all planets orbit the sun.

Tycho Brahe

thought that the sun and the moon rovolved around the Earth and that all other planets revolved around the sun.

Johannes Kepler

thought that all planets revolved around the sun in eliptical orbits and that the sun was not in the exact center of the orbits - also stated three laws of planetary motion.


one of the first to use telescopes to observe objects in space.

Isaac Newton

showed that all objects in the universe attract each other through gravitational force.

Edwin Hubble

proved that other galaxies existed beyond the edge of the Milky Way.


an instrument that collects electromagnetic radiation from the sky and concentrates it fo better observation.

refracting telescope

uses a set of lenses to gather and focus light from distant objects.

reflecting telescope

uses a curved mirror to gather and focus light from distant objects

focal point

the point where the rays of light that pass through the lens of that reflect from a mirror converge.

objective lens

collects light and forms an image at the back of the telescope.

electromagnetic radiation

the radiation associated with an electric and magnetic field


a region of the sky that contains a recognizable star pattern and that is used to describe the location of objects in space


the point in the sky directly above an observer on Earth


the angle between an object in the sky and the horizon


the line where the sky and the Earth appear to meet

celestial equator

an imaginary circle created by extending Earth's equator into space


apparent path of the sun across the sky throughout the year


measured in degrees north or south of the celestial equator

right ascension

measured n hours eastward from the vernal equinox

circumpolar stars

stars that can be seen at all times of the year and all times of night.


the distance that light travels in one year, about 9.46 trillion kilometers


occurs when a light source is moving quickly away from an observer


occurs when a light source is moving quickly toward and observer

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