Unit 3 Space Exploration Telescopes Unit 3 Space Exploration

1. History 2. Lenses & Hardware 3. Reflecting Telescopes 4. Refracting Telescopes

History of Telescopes Hans Lippershey Galileo Kepler Invented the “spyglass” (1608) Galileo The first to use a telescope in astronomy. Galileo’s improved the “spyglass” by designing a telescope with a combination of convex and concave lenses. (1609) Kepler Improved the design to have two convex lenses, which made the image upside-down. Kepler's design is still the major design of refractors today, with a few later improvements in the lenses and the glass to make them. (1611)

Crash Course Astronomy

Why can’t you see an object that is far away? The answer is simple: the object does not take up much space on retina, your eye’s screen. This can be corrected by bending the light with lenses.

Analogy Using a digital camera analogy, at 150 feet the writing on a dime does not cover enough pixels on your retinal sensor for you to read the writing.

Prior Knowledge Concave vs. Convex Lens

Lenses The lens in your eyes works like a glass lens. The light bends as it goes through a different medium. Light rays are bent when they intersect glass; a curved surface can produce an image. In your eye, the image is then focused at the retina.

How does this apply to telescopes? If you had a bigger eye, you could collect more light from the object. This image could be magnified so it stretches out over more pixels in your retina. In a telescope, two pieces make this possible: objective lens (refractor telescopes) or primary mirror (reflecting telescopes) the eye piece

The objective lens (in refractors) or primary mirror (in reflectors) collects lots of light from a distant object and brings that light, or image, to a point or focus. REFRACTOR TELESCOPE REFLECTOR TELESCOPE

An eyepiece lens takes the bright light from the focus of the objective lens or primary mirror and "spreads it out" (magnifies it) to take up a large portion of the retina.

Eyepiece Lens Analogy This is the same principle that a magnifying glass (lens) uses; it takes a small image on the paper and spreads it out over the retina of your eye so that it looks big.

(1) (3) (2) f Diagram of a simple telescope. Parallel light rays enter from the right, pass through the objective lens (1), come to a focus at the focal point (2), and exit through the eyepiece lens (3). The focal length of the objective is F, and the focal length of the eyepiece is f. www.ifa.hawaii.edu F

When you combine the objective lens or primary mirror with the eyepiece, you have a telescope. Again, the basic idea is to collect lots of light to form a bright image inside the telescope, and then use something like a magnifying glass to magnify (enlarge) that bright image so that it takes up a lot of space on your retina.

Properties of Telescopes Aperture – how well it can collect the light Magnification – how much it can magnify the image Which is more important?

The Aperture The aperture is the diameter of the lens or mirror used to gather light. Generally, the larger the aperture, the more light the telescope collects and brings to focus, and the brighter the final image.

Magnification The telescope's magnification is the ability to enlarge an image. It depends on the combination of lenses used. The eyepiece lens performs the magnification. The higher the number, the greater the magnification.

Which is more important? Since any magnification can be achieved by almost any telescope by using different eyepieces, aperture is a more important feature than magnification

The Powers of a Telescope Light Gathering Power – The ability of a telescope to collect a lot more light than the human eye. A large telescope can intercept and focus more starlight than does a small telescope. As a result, a larger telescope will produce brighter images and will be able to deduct fainter objects.

The Powers of a Telescope Resolving Power – is the capacity of an instrument to resolve two points which are close together. A large telescope also increases the sharpness of the image and the extent to which fine details can be distinguished.

The Powers of a Telescope Magnifying Power The ability of the telescope to make the object’s optical image appear bigger while being observed. A larger magnification does not improve the resolving power of the telescope.

A closer look at eyepieces What is different about the image?

Eyepiece The purposes of the eyepiece are to: produce and allow you to change the telescope's magnification produce a sharp image provide comfortable eye relief or the distance between your eye and the eyepiece when the image is in focus.

Telescope’s Field of View Apparent - how much of the sky, in degrees, is seen edge-to-edge through the eyepiece alone (specified on the eyepiece) True or real - how much of the sky can be seen when that eyepiece is placed in the telescope (apparent field/magnification)

Filters Filters are pieces of glass or plastic that you can place in the barrel of an eyepiece to restrict the wavelengths of light that come through in the image. Set of filters for viewing, including a light pollution filter (left) and colored filters for enhancing contrast in planetary images.

What are the benefits of filters? Enhance the viewing of faint sky objects in light-polluted skies. Enhance the contrast of fine features and details on the moon and planets Safely view the sun through their use. Example