Intro to Astro

1. Intro to Astro Cosmic Perspective and Telescopes

15. How fast are we moving with all this? • Daily Motion • Earth completes one rotation in 24 hours • Must move at close to 1000 miles per hour (1600 km/hr) at the equator (less at the poles) • Yearly Motion •  Earth's orbit is close to 600 million miles (970 million km) which we travel in one year • takes a speed of 66,000 miles per hour (107,000 km/hr) • Solar system motion • Moving within our Milky Way Galaxy • Sun and the Earth are moving at about 43,000 miles per hour (70,000 km/hr) • Orbiting in the Galaxy • Galaxy is in spinning motion like an enormous pinwheel • takes our Sun approximately 225 million years to make the trip around our Galaxy • Sun has to move is an astounding 483,000 miles per hour (792,000 km/hr) • Galactic movement • 1.3 million miles per hour (2.1 million km/hr)

16. Telescopes Essential question: How do scientists view far away and invisible objects in space? Warm-up: What is the most interesting thing you have seen in the night sky?

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

18. 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.

19. 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: • the objective lens (refractor telescopes) or primary mirror (reflecting telescopes) • the eye piece

20. 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. • 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. 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.

22. 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.

23. A telescope has two general properties • how well it can collect the light (the aperature) • how much it can magnify the image (the magnification)

24. The Aperture • A telescope's ability to collect light is directly related to the diameter of the lens or mirror -- the aperture -- that is 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.

25. Magnification • The telescope's magnification, its ability to enlarge an image, depends on the combination of lenses used. The eyepiece performs the magnification. Since any magnification can be achieved by almost any telescope by using different eyepieces, aperture is a more important feature than magnification

26. A closer look at eyepieces

27. 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. Filters can be used to: • 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

28. There are 2 main types of Telescopes • Refractor telescopes, which use glass lenses • Reflector telescopes, which use mirrors instead of lenses. Both types accomplish exactly the same thing, but in completely different ways.

29. Refractor Telescopes • Refractors are the type of telescope that most of us are familiar with. They have the following parts: • a long tube, made of metal, plastic, or wood • a glass combination lens at the front end (objective lens) • a second glass combination lens (eyepiece) • Refracting telescopes focus light rays by bending them with glass. (like a camera)

30. Refractor Telescopes Problems: - Lens can only be supported around edge. - "Chromatic aberration". - Some light absorbed in glass (especially UV, infrared). - Air bubbles and imperfections affect image quality.

31. This is the simplest telescope design you could have. A big lens gathers the light and directs it to a focal point and a small lens brings the image to your eye.

32. Refracting telescopes are not used for astronomical research (anymore) because they are large and have heavy lenses (i.e. expensive).

33. Reflecting telescopes focus light by bending them with mirrors - Can make bigger mirrors since they are supported from behind. - No chromatic aberration.

34. Refracting Telescope Reflecting Telescope Yerkes 40-inch (about 1 m). Largest refractor. Cerro-Tololo 4 -m reflector.

35. Not everything is visible… • Many modern day telescopes do not use visible light to collect images. • Radio telescopes, x-ray telescopes and infrared (IR) telescopes have become a staple of modern day astronomy, producing some amazing images. www.yorku.ca/eye/spectrum.gif

36. Famous Telescopes • Keck Telescope http://www.jpl.nasa.gov/events/lectures/dec04.cfm • Kitt Peak Observatory http://www.jpl.nasa.gov/events/lectures/dec04.cfm

37. Very Large Array (VLA)radio telescopes