Telescopes

Why Telescopes are Important We spend a lot of time talking about light and images But none of that does us any good if we don’t have a way of collecting that light in the first place This is where telescopes come in

What is a Telescope? So just what is a telescope? An object that uses lenses or reflecting surfaces to collect light from a distant object

The History of the Telescope It is a common misconception that Galileo invented the first telescopes In fact, Hans Lippershey, a Dutch spectacle make, is credited with designing the first telescope Galileo is the first person known to have turned a telescope to the sky(he gets the credit)

Galileo’s Telescope He was astonished by what he saw The rings of Saturn Stars in the Milky Way The moons of Jupiter Spots on the sun He also went blind-----

Can You Imagine? Just imagine what he must have felt, being the first person to see these things It was all completely unexpected----- Galileo’s observations, and those of others, would literally change the course of human history

Telescopes Today Telescopes have come a long way since then The biggest single telescopes have main mirrors that are over 12 meters in diameter! Some telescopes are actually arrays that are made of dozens of smaller telescopes linked together

Largest GranTeCan or GTC 10.4m

Keck 1 & 2 USA , Hi 10M

Tied for 3rd at 9. 2m The Hobby-Eberly Telescope or HET Ft Tied for 3rd at 9.2m The Hobby-Eberly Telescope or HET Ft. Davis, Texas

The Giant Magellan Telescope or GMT in 2020 will have 7-8 The Giant Magellan Telescope or GMT in 2020 will have 7-8.4m mirrors(24.5m)

Today, there are telescopes that are designed to see radio, microwave, infrared, visible, ultraviolet, x-ray and gamma-ray light? True False

How Telescopes Work There are two main types of telescopes Refracting telescopes use lenses to focus light to a point Reflecting telescopes use mirrors to focus the light Catadioptric telescopes are a combination of the two

Refracting and Reflecting Telescopes

Anatomy of a Telescope Although there are many types of telescopes, all have some basic key parts

Anatomy of a Telescope Aperture Primary Secondary Eyepiece Optical Tube Finder Detector

Anatomy of a Telescope The aperture is simply the part of the telescope that lets light in The primary bends the light, bringing the rays to a point The secondary aids in this process

Focusing Light The idea of focusing light is important Telescopes collect light from a large area By focusing the light, we concentrate its power The focal plane is the plane where the light rays meet The focal length is the distance from the primary lens (or mirror) to the focal plane

Focusing Light

Focusing Light

The Focal Plane If we put our eye at the focal plane, we would only see a bright point The eye piece straightens out the rays of light so our eye can see the image If we move the eyepiece out of the focal plane, the image will be distorted

Anatomy of a Telescope The optical tube protects the rest of the telescope and blocks stray rays of light The finder is a small telescope used for honing in on objects The detector is the thing that actually records the light Could be your eye

Common Reflectors

Some Other Telescope Properties There are some other properties of telescopes that astronomers are interested in Some of these things are Collecting Area Resolution Magnification Cost

What is the most important property of a telescope for astronomers? Magnification Collecting Area Focal Length

Collecting Area Collecting area is the area of the surface that the telescope uses to collect light This is usually the primary lens or mirror Many people think that magnification is the most important property of a telescope, but it is actually collecting area

Collecting Area Why is collecting area important? Suppose you are trying to see a very faint source If it is faint, then it is not sending many photons to Earth We need to collect as many photons as we can Having a large collecting area does this – like casting a big net to catch more fish

Collecting Area Most astronomical objects are pretty faint, so we need to collect as much light as we can

Resolution The resolution of a telescope defines how much detail we can see All optical systems have some resolution limit Eventually, the separation between objects becomes too small for us to see

Angular Size We measure the separation of objects in terms of angles Remember that there are 360° in a full circle There are 60 arc minutes in a degree, and 60 arc seconds in an arc minute So there are 3600 arc seconds for every degree of sky.

Back To Resolution Consider looking at a distant mountain Although the mountain is covered in trees, we cannot make out the trees themselves Our eyes have too low of a resolution