Science 9: Unit E: Space Exploration Topic 2 – Stronger Eyes and Better Numbers (Or, Telescopes and the Law of Universal Gravitation)

Telescopes  Telescopes exist to do two things: magnify distant objects, and collect as much light as possible from very dim sources of light. The bigger the telescope, the more light it collects.  The size of the telescope’s objective lens/mirror helps determine its resolving power. The larger the objective, the more detail you can see. To see any detail in Mars, for example, a 6” objective is minimum.

Telescopes Continued  A telescope collects light with its objective lens or mirror. This is the larger lens that light must refract through or reflect off of. The telescope we use has a 6” objective mirror.  A telescope focuses its light onto the eye of an observer through the eyepiece lens. The larger the eyepiece the better the image quality.

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

I. Refractor Telescope ObjectiveFeaturesAdvantagesDisadvantages Lens Collects light through a lens which is then focused onto the eyepiece. - Used by Galileo to support Heliocentric Model. Can produce the best quality images. - Very expensive to make larger objective lenses. - Color of objects is often distorted (Halo).

II. Reflector Telescope ObjectiveFeaturesAdvantagesDisadvantages Mirror - Collects light through a concave mirror which is then focused onto a secondary mirror and finally passed to the eyepiece lens. - Invented by Newton. Much cheaper than refractors. - Can be made much larger, and therefore can see deeper into space. - Images not as sharp as with refractors.

III. Combination Telescopes ObjectiveFeaturesAdvantagesDisadvantages Mirror Light first focused by lens onto concave objective mirror which is then reflected onto secondary mirror and finally focused through opening in objective mirror to eyepiece. Produces good quality images. Produces good quality images. Very powerful for its size Very powerful for its size - Expensive.

Significance of Telescopes Without the telescope Galileo could not make his discoveries supporting the Heliocentric Model. In particular he discovered that: Without the telescope Galileo could not make his discoveries supporting the Heliocentric Model. In particular he discovered that:  The planets, moon, and sun were not perfect objects in space.  Objects orbit the sun or other planets (Jupiter’s moons). Not the Earth.  Saturn has rings

Calculating Magnification of a Telescope  Focal Length of a telescope – the length that light has to travel before it hits the objective lens or mirror.  Focal Length of an Eyepiece – The diameter of an eyepiece lens.  Magnification of a telescope is found by:  Magnification = Focal length of telescope  Focal Length of eyepiece.

Magnification Example  Eg. Mr. Branco’s telescope has a focal length of 1200 mm. If he uses an eyepiece with a 25 mm focal length, what is his magnification?  M = 1200 mm  25 mm = 48X

Resolving Power  - The ability to capture greater detail. The larger the objective, the greater the resolving power of the telescope. EyeEye BinocsBinocs TELeTELe

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

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

The Universal Law of Gravity  Isaac Newton, discovered the law that explained how gravity works between all objects.  Newton’s law says that any two objects will have an attractive gravitational force between them.  Let’s say you were alone in empty space except for a pencil. The pencil and you would move closer together. Let’s say that you threw the pencil as far away as possible. It would eventually come back.

The Universal Law of Gravity  The more mass an object has, the more it pulls on other objects. That’s why we don’t crash into each other, because our masses are all so small compared to the Earth.  The same things applies to the planets, they are kept in their orbits by their attraction to the massive sun. The only reason they don’t crash into the sun is because they are constantly in motion.

Universal Law of Gravity Fun Fact: G (6.67* ), 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.