Telescopes Chapter 5

Objectives   Telescopes……………Chapter 5 Objectives:   1. To list the parts of a telescope.   2. To describe how mirrors aid in telescope magnification.   3. To describe three different types of telescopes.   4. To construct a simple telescope.

What do you think of when someone asks you about a telescope?  Some of these terms should come to mind:       

Types of telescopes    Interferometers ( not a type of telescope, but decrease light interference )  Radio telescopes  

Telescopes  The most basic telescopes work by gathering light, then focusing and/or “ bending light ” onto a particular spot.  This causes an increase in the magnification of an image.

What are the two most important properties of a telescope? 1. ______________________________: Also called Collecting Power. Telescopes with a larger collecting area can gather a greater amount of light in a shorter time. 2. _______________________________: Also called Resolving Power. Telescopes that are larger are capable of taking images with greater detail.

Determining a good telescope  _______________________ – how much more light that a telescope can gather than the human eye.  The larger the lens, the more collecting power This allows for a brighter image (easier for you to see)This allows for a brighter image (easier for you to see) This is the primary reason for making telescopes larger.This is the primary reason for making telescopes larger.  Telescopes are first described by the diameter of its light collecting device (mirror or lens)  Once light is collected then it must be focused.

Determining a good telescope  How light is focused  ___________________ – Light is focused to form a particular image using a lens. Relies on the process of ___________________ which is the bending of light when it goes through different media. Occurs because the speed of light changes when it enters the lens.Relies on the process of ___________________ which is the bending of light when it goes through different media. Occurs because the speed of light changes when it enters the lens. Refraction also spreads the light out. Results in the colors of the rainbow.Refraction also spreads the light out. Results in the colors of the rainbow. ___________________– The spreading of light or other electromagnetic radiation into a spectrum.___________________– The spreading of light or other electromagnetic radiation into a spectrum.  The light rays are bent when they go through one media (air) and then another (glass)

Refracting Telescopes  Use _______________ to focus light  Are limited by the size and quality of the lens.  Most modern telescopes are reflecting telescopes as opposed to refracting telescopes.

Focusing Light  A camera focuses light like an eye and captures the image with a detector.  Because we can control the exposure time (amount of time the light collects on the detector), a camera can record details that are too faint to see with our eyes alone.  The CCD detectors in digital cameras are similar to those used in modern telescopes. Cameras detect light with charge- coupled devices (CCDs).

Determining a good telescope  Besides collecting light, telescopes also allow us to discern objects as single large object or several small individuals  ______________________________ – The ability of a telescope or instrument to discern fine details. Larger diameter telescopes have greater resolving power than smaller ones. Resolving power is limited because light waves can be diffracted.Resolving power is limited because light waves can be diffracted. Diffraction –Diffraction – Diffraction limits the resolving power of a telescope.Diffraction limits the resolving power of a telescope.

Reflecting telescopes  Use __________________ to collect and focus light.  Reflectors are slightly curved mirrors  Light does not go through them and as a result is not dispersed.  Most telescopes today are reflecting  Multiple mirrors bounce the light around, each time bending it slightly and thus magnifying the image.

Atmospheric Refraction  Occurs for objects viewed in the sky.  The gases of the atmosphere bend light and change the appearance of an object  ________________________ refraction makes the sun look higher in the sky than it really is.  Atmospheric refraction is stronger closer to the horizon. Causes the sun to look flat as it sets.

Interferometers  A device consisting of ____________ ______________________ connected together to work as a single instrument.  Allow for a high resolving power, the ability to see small scale features.  Can be used to increase the power of radio, infrared, and visible wavelengths.

Observatories  As far as telescopes discussed by the groups, for the test, make sure to look over the telescopes and observatories discussed in the book.  Remember that SEVERAL telescopes are located in Hawaii (Mauna Kea)  Why are so many telescopes in HI? 

Light Pollution  ___________________________ is city light scattering off the atmosphere and into a telescope.  Scattering of human-made light in the atmosphere is a growing problem for astronomy when using land-based telescopes.

Why do we put telescopes into space?

Benefits of Space Telescopes  Only radio and visible light pass easily through Earth’s atmosphere. We need telescopes in space to observe other forms. 

Non optical telescopes  Most X rays and UV light is absorbed by the atmosphere.  Radio waves can penetrate the atmosphere.  Gamma ray telescopes measure gamma rays that are released during nuclear explosions.  These explosions occur during stellar evolution.