# Telescopes

##### Study Tip
Think of wavelength as the length between two corresponding points on a wave (i.e. From the top of one wave to the top of the next). Remember, frequency how frequently as how frequent a wave shows up after one second.

• Electromagnetic (EM) radiation is energy that is transmitted through space as a wave
• e.g. light
• Two components, electric field and magnetic field, which oscillate between positive and negative values
• Wavelength: distance between two adjacent oscillations
• Frequency: measures the number of wavelengths that pass a given point every second
• Wavelength and frequency are reciprocal (as one increases, the other decreases)
##### Study Tip
Think of wavelength as the length between two corresponding points on a wave (i.e. From the top of one wave to the top of the next). Remember, frequency how frequently as how frequent a wave shows up after one second.
• Visible light: the light humans can see; comes in a variety of colors
• Color determined by wavelength
• Visible light ranges from wavelengths of 400 nm to 700 nm (colors violet to red)
• Electromagnetic spectrum: full range of electromagnetic radiation
• Like our Sun, every star emits light at a wide range of wavelengths. Astronomers can learn a lot from studying the details of the spectrum of light from a star. (a) Visible light is part of the electromagnetic spectrum, which ranges from gamma rays with very short wavelengths, to radio waves with very long wavelengths. (b) These are images of the same scene. In the top, only the wavelengths of visible light show. In the bottom, a layer of thick clouds

## Types of Telescopes

• Optical telescopes
• Refracting telescopes rely on the refraction, or bending, of light by lenses
• Reflecting telescopes rely on the reflection of light by the use of mirrors, which is significant because
• Mirrors are lighter than heavy glass lenses in refractors
• Mirrors are easier to make precisely than glass lenses
• Because they do not need to be as heavy to support the same size lens, reflectors can be made larger than refractors. Large telescopes can collect more light and thus be used to study dimmer and more distant objects. Reflecting telescopes on top of Mauna Kea in Hawaii

## Earth Science

• Radio telescopes (collect and focus radio waves or microwaves, the waves with the shortest wavelength)
• Larger telescopes which are built to collect light at longer wavelengths
• A group of radio telescopes can be linked together with a computer so that they are all observing the same object
• Space telescopes (orbit outside the Earth’s atmosphere)
• Avoids issue of Earth’s atmosphere blocking radiation and distorting light
• Can carry instruments to observe objects emitting various types of EM radiation (a) The Hubble Space Telescope orbits Earth at an altitude of 589 km (366 mi).
It collects data in visible, infrared, and ultraviolet wavelengths.
(b) This starburst cluster is one of the many fantastic images
taken by the HST over the past two decades.
##### Concept Check
• Describe each of the types of telescopes discussed here: reflecting, refracting, radio, and space.
• What are the limitations of each type of telescope discussed here?
• Look at the electromagnetic spectrum. Do you think other types of telescopes could obtain new information by gathering different wavelengths?