Science 9: Unit E: Science 9: Unit E: Space ExplorationSpace Exploration

Topic 2 – Stronger Eyes and Better Topic 2 – Stronger Eyes and Better Numbers (Or, Telescopes and the Law of Numbers (Or, Telescopes and the Law of

Universal Gravitation)Universal Gravitation)

TelescopesTelescopes

Telescopes exist to do two things: magnify Telescopes exist to do two things: magnify distant objects, and collect as much light distant objects, and collect as much light as possible from very dim sources of light. as possible from very dim sources of light. The bigger the telescope, the more light it The bigger the telescope, the more light it collects.collects.

The size of the telescope’s objective The size of the telescope’s objective lens/mirror helps determine its resolving lens/mirror helps determine its resolving power. The larger the objective, the more power. The larger the objective, the more detail you can see. To see any detail in detail you can see. To see any detail in Mars, for example, a 6” objective is Mars, for example, a 6” objective is minimum.minimum.

Telescopes ContinuedTelescopes Continued

A telescope collects light with its objective A telescope collects light with its objective lens or mirror. This is the larger lens that lens or mirror. This is the larger lens that light must refract through or reflect off of. light must refract through or reflect off of. The telescope we use has a 6” objective The telescope we use has a 6” objective mirror. mirror.

A telescope focuses its light onto the eye A telescope focuses its light onto the eye of an observer through the eyepiece lens. of an observer through the eyepiece lens. The larger the eyepiece the better the The larger the eyepiece the better the image quality.image quality.

Types of telescopesTypes of telescopes

There are three main types of There are three main types of telescopes, each with their own telescopes, each with their own advantages and disadvantages.advantages and disadvantages.

I. Refractor TelescopeI. Refractor Telescope

Objective Objective Features Features Advantages Advantages DisadvantageDisadvantages s

Lens Lens Collects light Collects light through a lens through a lens which is then which is then focused onto focused onto the eyepiece.the eyepiece.

- Used by - Used by Galileo to Galileo to support support Heliocentric Heliocentric

Model.Model.

Can Can produce the produce the best quality best quality images. images.

- Very expensive - Very expensive to make larger to make larger objective lenses.objective lenses.

- Color of objects - Color of objects is often distorted is often distorted (Halo). (Halo).

II. Reflector TelescopeII. Reflector Telescope

Objective Objective Features Features Advantages Advantages Disadvantages Disadvantages

Mirror Mirror -Collects light Collects light through a through a concave mirror concave mirror which is then which is then focused onto a focused onto a secondary secondary mirror and mirror and finally passed finally passed to the eyepiece to the eyepiece lens.lens.-Invented by Invented by Newton.Newton.

Much cheaper Much cheaper than than refractors.refractors.

- Can be made - Can be made much larger, much larger, and therefore and therefore can see can see deeper into deeper into space.space.

- Images not - Images not as sharp as as sharp as with with refractors. refractors.

III. Combination TelescopesIII. Combination Telescopes

ObjectiveObjective FeaturesFeatures AdvantagesAdvantages DisadvantagesDisadvantages

Mirror Mirror Light first Light first focused by focused by lens onto lens onto concave concave objective objective mirror which is mirror which is then reflected then reflected onto secondary onto secondary mirror and mirror and finally focused finally focused through through opening in opening in objective objective mirror to mirror to eyepiece. eyepiece.

Produces Produces good good quality quality images.images.

Very Very powerful powerful for its size for its size

- Expensive. - Expensive.

Significance of TelescopesSignificance of Telescopes

Without the telescope Galileo could not Without the telescope Galileo could not make his discoveries supporting the make his discoveries supporting the Heliocentric Model. In particular he Heliocentric Model. In particular he discovered that:discovered that:

The planets, moon, and sun were not The planets, moon, and sun were not perfect objects in space.perfect objects in space.

Objects orbit the sun or other planets Objects orbit the sun or other planets (Jupiter’s moons). Not the Earth.(Jupiter’s moons). Not the Earth.

Saturn has ringsSaturn has rings

Calculating Magnification of a Calculating Magnification of a TelescopeTelescope

Focal Length of a telescope – the length Focal Length of a telescope – the length that light has to travel before it hits the that light has to travel before it hits the objective lens or mirror.objective lens or mirror.

Focal Length of an Eyepiece – The Focal Length of an Eyepiece – The diameter of an eyepiece lens.diameter of an eyepiece lens.

Magnification of a telescope is found by:Magnification of a telescope is found by: Magnification = Focal length of Magnification = Focal length of

telescope telescope Focal Length of eyepiece. Focal Length of eyepiece.

Magnification ExampleMagnification Example

Eg. Mr. Branco’s telescope has a Eg. Mr. Branco’s telescope has a focal length of 1200 mm. If he uses focal length of 1200 mm. If he uses an eyepiece with a 25 mm focal an eyepiece with a 25 mm focal length, what is his magnification?length, what is his magnification?

M = 1200 mm M = 1200 mm 25 mm = 48X 25 mm = 48X

Resolving PowerResolving Power

- The - The ability to ability to capture capture greater greater detail. The detail. The larger the larger the objective, objective, the the greater greater the the resolving resolving power of power of the the telescope.telescope.

Eye

Binocs

T

E

L

e

Problems with the Heliocentric ModelProblems with the Heliocentric Model

Copernicus thought as many did, Copernicus thought as many did, that circles were the perfect shape. that circles were the perfect shape. Because of this he made the planet’s Because of this he made the planet’s orbits circular, however the planets’ orbits circular, however the planets’ orbits did not appear to be circular, orbits did not appear to be circular, so Copernicus again relied on so Copernicus again relied on epicycles to explain this problem. His epicycles to explain this problem. His model was no better at explaining model was no better at explaining how things worked than the old how things worked than the old Geocentric Model.Geocentric Model.

Problems with the Heliocentric Model Cont’dProblems with the Heliocentric Model Cont’d

Through the work of German scientist Through the work of German scientist Johannes Kepler, the truth about the Johannes Kepler, the truth about the planets’ orbits came out: they were planets’ orbits came out: they were ellipses or oval. This is because of the ellipses or oval. This is because of the force of gravity pulling the planets to the force of gravity pulling the planets to the sun. The planets speed up the closer they sun. The planets speed up the closer they get to the sun and slow down as they get to the sun and slow down as they move away from it. This explains the move away from it. This explains the changing speed of the planets in the sky.changing speed of the planets in the sky.

The Universal Law of GravityThe Universal Law of Gravity

Isaac Newton, discovered the law that Isaac Newton, discovered the law that explained how gravity works between all explained how gravity works between all objects. objects.

Newton’s law says that any two objects Newton’s law says that any two objects will have an attractive gravitational force will have an attractive gravitational force between them. between them.

Let’s say you were alone in empty space Let’s say you were alone in empty space except for a pencil. The pencil and you except for a pencil. The pencil and you would move closer together. Let’s say that would move closer together. Let’s say that you threw the pencil as far away as you threw the pencil as far away as possible. It would eventually come back.possible. It would eventually come back.

The Universal Law of GravityThe Universal Law of Gravity

The more mass an object has, the more it The more mass an object has, the more it pulls on other objects. That’s why we don’t pulls on other objects. That’s why we don’t crash into each other, because our masses crash into each other, because our masses are all so small compared to the Earth.are all so small compared to the Earth.

The same things applies to the planets, The same things applies to the planets, they are kept in their orbits by their they are kept in their orbits by their attraction to the massive sun. The only attraction to the massive sun. The only reason they don’t crash into the sun is reason they don’t crash into the sun is because they are constantly in motion.because they are constantly in motion.

Universal Law of GravityUniversal Law of Gravity

Fun Fact: G (6.67*10-11 ), not to be confused with g (9.8 N/kg) is one of the universe constants that if it were just a little bit off, the universe as we know it could not exist.