Chapter 2: Light and Telescopes

A blackbody emits all its radiation at a single frequency.

Earth's atmosphere is transparent to all forms of electromagnetic radiation.

The peak of an object's emitted radiation occurs at a frequency determined by the object's temperature.

Imagine an emission spectrum produced by a container of hydrogen gas. Changing the amount of hydrogen in the container will change the colors of the lines in the spectrum.

The wavelengths of the emission lines produced by an element are different from the wavelengths of the absorption lines produced by the same element.

As a rule, larger telescopes can detect fainter objects.

An object having a temperature of 300 K would be best observed with an infrared telescope.

Visible light is a particular type of [blank_start]electromagnetic[blank_end] radiation and travels through space in the form of a [blank_start]wave[blank_end].

A [blank_start]wave[blank_end] is characterized by its [blank_start]period[blank_end], the length of time taken for one complete cycle; its [blank_start]wavelength[blank_end], the distance between successive wave crests; and its [blank_start]amplitude[blank_end], which measures the size of the disturbance associated with the wave.

A wave's [blank_start]frequency[blank_end] counts the number of wave [blank_start]crests[blank_end] passing a given point in one second.

A beam of white light is bent, or [blank_start]refracted[blank_end], as it passes through a prism.

Different frequencies of light are refracted by different amounts, splitting light into its component colors: the [blank_start]visible[blank_end] spectrum.

The color of visible light indicates its wavelength: red light has a [blank_start]longer[blank_end] wavelength than blue light.

The entire [blank_start]electromagnetic[blank_end] spectrum consists of (in order of increasing frequency) [blank_start]radio waves[blank_end], [blank_start]infrared radiation[blank_end], [blank_start]visible light[blank_end], [blank_start]ultraviolet radiation[blank_end], [blank_start]X-rays[blank_end], and [blank_start]gamma rays[blank_end].

The [blank_start]temperature[blank_end] of an object is a measure of the speed of its component particles.

The intensity of radiation of different frequencies emitted by a hot object has a characteristic distribution, called a [blank_start]blackbody[blank_end] [blank_start]curve[blank_end], that depends only on the object's temperature.

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

A [blank_start]spectroscope[blank_end] is a device for splitting a beam of radiation into its component frequencies and displaying them on a screen or detector for detailed study.

Many hot objects emit a continuous [blank_start]spectrum[blank_end] of [blank_start]radiation[blank_end], containing light of all [blank_start]wavelengths[blank_end].