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Stars grouped into patterns


A device that determines the position and motion of the heavenly bodies


Sextant and octant were handheld instruments having a movable index arm that indicated the angle of elevation between a star the sun or moon and the horizon

Refractor telescope

The telescope Galileo Galilei invented


Make (a ray of light) change direction when it enters at an angle.

Objective lens

the lens or system of lenses in a telescope or microscope that is nearest the object being viewed.


Eye piece or magnifying lens


The ability of a telescope to bring out details in an image

Wave length

A slightly different angle of refraction in a given lens

Compound lens

Moderns refractors avoid chromatic aberration by using special lenses consisting of two different kinds of glass cemented together

Reflector telescope

Telescope that Sir Issac Newton created

Newtonian reflector

The arrangement in which the image is viewed through the side of a tube

Cassegrainian reflector

A more compact reflector telescope design that is easier to use

Composite telescope

A telescope that uses both mirrors and correcting objective lens to gather light

Schmidt-cassegrainian telescope

In this form the light path enters the telescope through a special lens and then continues through a hole in the main mirror as with a standard cassegrainian

Radio telescope

An instrument used to detect radio emissions from the sky, whether from natural celestial objects or from artificial satellites

Hubble space telescope

A special instrument that spans the optical and nonoptical categories of telescopes


The astronomical equivalent of latitude and longitude

Celestial equator

When the heavens are divided into northern and southern halves


A stars angular distance north or south of the celestial equator

Right ascension

A stars longitudinal position

Prime hour circle

The starting line for right ascension


A measure of its relative brightness

Red shift

The mathematical rule that relates the stretching of wavelengths of their light with increasing distances

Proper motion

Movements across the sky as we see it

Radial motion

Movement directly toward or away from us


The color of a star

Super giant

A red star that is five times larger than the sun

White dwarf

Some very hot blue white stars are that are relatively small

Eclipsing binaries

Variable star pairs like Agol

Cepheid variables

Stars that expand and contract regularly


How long a star takes to go from one bright spurt to the next


Occasionally a star may increase it brightness by twenty magnitudes or more in an explosion that practically destroys the star


A star that will be visible for several month or years that no one has recorded then it will fade away

Neutron star

An extremely dense small dark star in which atomic particles (electrons and protons) have combined to from neutrons

Star cluster

Several stars that have the same motions


Consists of millions of stars


The many types of objects that Messier and Dreyer cataloged which are clouds of gas and or dust


A massive and extremely remote celestial object, emitting exceptionally large amounts of energy and typically having a starlike image in a telescope

Black hole

The most mysterious and unusual objects in the universe.

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