Chapter 2.

emission line

Bright line in a specific location of the spectrum of radiating material, corresponding to emission of light at a certain frequency. A heated gas in a glass container produces emission lines in its spectrum.

atom

Building block of matter, composed of positively charged protons and neutral neutrons in the nucleus surrounded by negatively charged electrons.

telescope

Instrument used to capture as many photons as possible from a given region of the sky and concentrate them into a focused beam for analysis.

spectroscope

Instrument used to view a light source so that it is split into its component colors.

temperature

A measure of the amount of heat in an object, and an indication of the speed of the particles that comprise it.

proton

An elementary particle carrying a positive electric charge, a component of all atomic nuclei. The number of protons in the nucleus of an atom dictates what type of atom it is.

nucleus

Dense, central region of an atom, containing both protons and neutrons, and orbited by one or more electrons.

photon

Individual packet of electromagnetic energy that makes up electromagnetic radiation.

gamma ray

Region of the electromagnetic spectrum, far beyond the visible spectrum, corresponding to radiation of very high frequency and very short wavelength.

ultraviolet

Region of the electromagnetic spectrum, just beyond the visible range, corresponding to wavelengths slightly shorter than blue light.

high-energy telescope

Telescope designed to detect X- and gamma-ray radiation.

infrared telescope

Telescope designed to detect infrared radiation. Many such telescopes are designed to be lightweight so that they can be carried above (most of) Earth's atmosphere by balloons, airplanes, or satellites.

angular resolution

The ability of a telescope to distinguish between adjacent objects in the sky.

blackbody curve

The characteristic way in which the intensity of radiation emitted by a hot object depends on frequency. The frequency at which the emitted intensity is highest is an indication of the temperature of the radiating object. Also referred to as the Planck curve.

wave

A pattern that repeats itself cyclically in both time and space. Waves are characterized by the speed at which they move, their frequency, and their wavelength.

ultraviolet telescope

A telescope that is designed to collect radiation in the ultraviolet part of the spectrum. Earth's atmosphere is partially opaque to these wavelengths, so ultraviolet telescopes are put on rockets, balloons, and satellites to get high above most or all of the atmosphere.

molecule

A tightly bound collection of atoms held together by the atoms' electromagnetic fields. Molecules, like atoms, emit and absorb photons at specific wavelengths.

neutron

An elementary particle with roughly the same mass as a proton, but which is electrically neutral. Along with protons, neutrons form the nuclei of atoms.

electromagnetic radiation

Another term for light, electromagnetic radiation transfers energy and information from one place to another.

interferometer

Collection of two or more telescopes working together as a team, observing the same object at the same time and at the same wavelength. The effective diameter of an interferometer is equal to the distance between its outermost telescopes.

absorption line

Dark line in an otherwise continuous bright spectrum, where light within one narrow frequency range has been removed.

radio wave

Electromagnetic radiation with wavelength in the radio part of the spectrum

radio telescope

Large instrument designed to detect radiation from space at radio wavelengths.

X-ray

Region of the electromagnetic spectrum corresponding to radiation of high frequency and short wavelength, far beyond the visible spectrum.

infrared

Region of the electromagnetic spectrum just outside the visible range, corresponding to light of a slightly longer wavelength than red light.

continuous spectrum

Spectrum in which the radiation is distributed over all frequencies, not just a few specific frequency ranges. A prime example is the blackbody radiation emitted by a hot, dense body.

electromagnetic spectrum

The complete range of electromagnetic radiation, from radio waves to gamma rays, including the visible spectrum. All types of electromagnetic radiation are basically the same phenomenon, differing only by wavelength, and all move at the speed of light.

wavelength

The distance from one wave crest (or trough) to the next, at a given instant in time.

frequency

The number of wave crests passing any given point in a unit time.

emission spectrum

The pattern of spectral emission lines produced by an element. Each element has its own unique emission spectrum.

visible light

The small range of the electromagnetic spectrum that human eyes perceive as light. The visible spectrum ranges from about 400-700 nm, corresponding to blue through red light.

period

The time needed for an orbiting body to complete one revolution about another body.

collecting area

The total area of a telescope capable of capturing incoming radiation. The larger the telescope, the greater its collecting area, and the fainter the objects it can detect.