Astronomy & Cosmology Topic 5.1 : Telescopes

Telescopes

used to magnify distant objects and capture more light than the human eye can collect

When was first telescope made and how?

Around 1608

Dutch optician put two lenses in line with each other and looked through them

When did Galileo make first useable telescope

In 1609. It was equivalent to modern binoculars. It had 20-30x magnification

What was the first telescope used for?

To look at the moon and realized it had craters

What did Galileo realize about Jupiter?

It had 4 points of light that moved around. it

What are the largest moons of Jupiter?

Galilean moons

Callisto, Ganymede, Io, Europa

Why did it contradict Greek philosophers?

They believed everything went around/orbited the Earth, yet the Earth orbited the Sun instead.

What did Galileo see about the Sun?

Saw sunspots. Claimed sun was "imperfect"

What did Galileo see with Venus?

He saw phases of Venus (different parts lit up). He saw the size of Venus changing over time

What does size changing mean?

Venus is not going around the Earth. This contradicts geocentric ideas that all planets orbit the Earth.

How do telescopes work?

Objects in space are far enough that all the light rays coming from them can be considered parallel to each other

What is a lens

A device made of transparent material that bend rays of light

How does a converging lens work

makes parallel rays of light converge towards a location called the focus

The stronger the lens

the shorter the focal length

Refraction

lenses bend light in this process

What happens to light when it goes through a prism

it bends

How are different wavelengths of light refracted?

by different amounts through any material

How much are red (longer wavelengths) refracted?

bent & refracted the least

How much are blue (shorter wavelengths) refracted?

bent and refracted the most

What can a lens be thought of?

as many prisms

What is the focus

they bend parallel lightrays towards a point

What is the length the focus is away from?

one focal length from the lens

Where are the converging lenses?

thick in the middle, thin at the edges

What are converging/convex lenses used for?

in glasses for far sighted people (reading glasses), magnifying lenses

How do parallel rays diverge ffom each other

as if they are coming from a point (the focus)

What are diverging/concave lenses used for

used in glasses for short sighted people

How does the converging lens in the front work?

It can chanfge its focal length

What does it allow the converging lenses to do?

It converge rays of light from far away and from close by onto the retina in the back

How do you correct the vision system?

When the lens don't work, you need an extra lens in front

What are the 2 main functions of a telescope?

Gather more light than the human eye can

Magnify distant objects

What are simple refracting telescopes made of?

One large lens and one small lens. We look through small lens

What do the objective lens do in a telescope?

They gather a lot of parallel rays of light and converges it to a point to make an image. The more light it gathers, the brighter and clearer the final image is

What does the smaller eyepiece lens act like?

A magnifying glass and makes image larger for us to see

Aperture

The size of the opening to the objective lens

The bigger the aperture,

the more light that is collected through the telescope

What does the large aperture mean?

more brightness (since you are getting more light)

more detail in the image

Pros of refractors

really great contrast & image quality

no maintenance required (both sides are sealed with lenses, no dust can get in)

simplest design for a telescope

Cons of refractors

large lenses are difficult to build and grind

heavy since the lenses are solid glass. this puts an upper limit on how big they can be since eventually their mounts are not strong enough to hold them up

chromatic aberration

Chromatic Aberration

The rainbow effect where lenses bend light of different wavelengths at different focal points. This makes different colors form images at slightly different places. It can be seen in strong eye-glasses.