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Stargazing 101

Stargazing 101

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Stargazing 101

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  1. Stargazing 101 “Stargazing Equipment” Chapter 5 September 22, 2009

  2. What did you see this past week? September 2009 www.OrionTelescope.com

  3. Viewing the Stars • Naked-eye viewing • Binoculars • Telescopes

  4. Viewing the Stars – Naked-eye • Naked-eye viewing is the best way to start • Need to start with the big picture • See the entire sky, piece by piece • Learn the relative positions of stars and constellations to each other • After awhile you will know where to look for the various stars and constellations • Don’t rush into buying equipment

  5. Star Brightness – Little Dipper Kochab • Sky conditions affect star visibility • Light pollution, moisture in air and atmospheric turbulence can make stars appear dimmer. • To “rate” sky conditions on a particular night use the Little Dipper – Polaris [2.0] • Compare the stars you see with the diagram • What is the dimmest star you can see? • Naked-eye limit is around 6 magnitude on the clearest, darkest nights Orion Catalogue

  6. Viewing the Stars – Binoculars • Binoculars • Very useful midway point between naked-eye viewing and a telescope • Great way to start (before buying telescope) • See more detail on the Moon • See four of Jupiter’s moons • Very useful for seeing open star clusters, like the Pleiades (maybe the best view), and many double stars, not visible to the naked eye • Colors of stars are more evident • Stars will still be points of light

  7. Binoculars • Binocular sizes • Expressed in two numbers, such as 10x50 • The first number is the magnification (or power) • The second is the diameter (aperture) of the front lens, in millimeters • Thus, a 10x50 binocular provides 10-times magnification and has a 50mm aperture

  8. Binoculars • Binocular sizes • Magnification • 7x or 8x – somewhat steady image, when hand-held • 10x – shaky and may need to be mounted on tripod. • 12x or greater, you will need to mount it on a tripod • The author recommends 10x maximum Tripod mount NightWatch, p. 62-63

  9. Binoculars • Binocular sizes • Aperture • The larger the aperture (front lens) the brighter the images will appear • The more light gets to your eye • For stargazing, the author recommends 40-50mm Aperture, in mm

  10. Binoculars – Types • There are two main types of binoculars • Porro prisms • Roof prisms • Prisms, in binoculars, turn what would be an upside-down image, right-side up.

  11. Binoculars –Porro prisms • Porro prisms are easier to align precisely at the factory • So, Porro prism binoculars tend to cost less for a given size • But, they also tend to be heavier than roof prism binoculars Orion Catalogue

  12. Binoculars – Roof prisms • Roof prisms binoculars have a more streamlined shape • Tend to be lighter • Tend to be more expensive • Roof prisms lose slightly more light to reflection than Porro prisms. • This is a disadvantage for astronomical use Orion Catalogue

  13. Binoculars – lens coatings • Anti-reflection lens coatings produce much better images • Increase light transmission through lens • Reduce internal reflections that cause ghost images • Adds to cost of good binoculars, but well worth it.

  14. How to use binoculars • Fix your sight on the object you want to see through the binocular. • With your sight fixed on the object, move the binoculars between your eyes and the object, without looking away. • Do not move your head • If you don’t “nail” the object, bring the binoculars down and try again. • Practice in the daytime, on a variety of objects. • Harder at night, because stars look pretty much the same

  15. Novel ways to steady binoculars • The author recommends using: • A reclining lawn chair • A child-size inflatable dinghy NightWatch, p. 62

  16. Selecting binoculars • Some questions to consider when deciding on particular binoculars: • How heavy are they, for their size? • Are they easy or awkward to use? • Are they difficult to focus? • Are objects at the edge of the field distractingly fuzzy, even though the center of the field is in focus? • And, the Bottom Line: How much do you want to spend? • Best to plan to spend around $100 or more

  17. Selecting binoculars • “Binoculars under $100” • Astronomy Magazine, April 2005

  18. Viewing the Stars–Telescopes Orion Catalogue

  19. 3. Telescopes • Three distinct types of telescopic power • Collecting Power (also called light gathering power or light grasp) • Magnifying Power • Resolving Power

  20. 1. Collecting Power • Collecting Power=the amount of light the telescope is able to focus into the eyepiece • The more light it collects, the brighter the image • Stars will always look like points of light, but you will be able to see more (fainter ones) and they will be brighter • This is the mostsignificant factor Explorations: An Introduction to Astronomy, Thomas T. Arny, p. 155)

  21. 1. Collecting Power • Light-collecting ability varies with the square of the aperture. • Thus, a 90mm telescope (a little under 4”) collects only 1/5 as much light as an 8” telescope Orion Catalogue

  22. 2. Magnifying Power • Magnifying Power= the number of times a telescope (or binocular) can increase the apparent size of an object. • 8x, 100x, etc. • We’ll discuss how to calculate magnifying power later.

  23. 3. Resolving Power • Resolving Power = the ability of the instrument to discriminate fine detail. • How sharp or fuzzy the image is • The limitation on resolving power is imposed by the interaction of light and optics. • The quality of the optics is a major factor • Lens, mirrors, eyepieces, etc. • Usually, you get what you pay for • The turbulence in the air column you are looking through, moisture in the air, etc. also effect this.

  24. 3. Resolving Power http://physics.uoregon.edu

  25. Types of Telescopes • Three basic types of telescopes • Refractors • Reflectors • Cassegrains(catadioptric) • Maksutov-Cassegrain • Schmidt-Cassegrain

  26. Telescopes - Refractors • Refractors– Use two or more lens to bend (refract) the light, so it focuses on the eyepiece at the end of the telescope. • Usually the least expensive • Since there are no mirrors, they can have the most distortion-free images • Good for both astronomy and terrestrial viewing • Other telescopes invert or reverse the image Orion Catalogue

  27. How a lens focuses light • A lens bends (or refracts) the light and focuses it on a point Focal Point Explorations: An Introduction to Astronomy, Thomas T. Arny, p. 155)

  28. Telescopes - Refractors • 60mm Refractor(2.4”) • Meade model 285 • Light Grasp = 4.4 sq. inches • Focal length = 900mm www.meade.com

  29. Telescopes - Reflectors • Reflectors– gather light at the primary mirror (curved) on the far end of the tube, which focuses the image onto the secondary mirror (flat), that redirects the light at a right angle into the eyepiece, mounted on the side of the telescope. Orion Catalogue

  30. Telescopes - Reflectors • Reflectors • Also called Newtonian Reflectors • First designed by Isaac Newton, around 1670 • The best light-gathering capability • Quality of mirrors very critical • Good for astronomy viewing only • They invert the image (objects look upside down) Orion Catalogue

  31. How a curved mirror focuses light • Mirrors that are made of glass that has been shaped to a smooth curve, polished and then coated with a thin layer of aluminum or some other highly reflective material Focal Point Explorations: An Introduction to Astronomy, Thomas T. Arny, p. 158)

  32. Telescopes - Reflectors • 6 inch Reflector • Orion® AstroViewTM 6 EQ Reflector • Light Grasp = 27.4 sq. inches • Focal length = 750 mm • Weight = 39 pounds • (telescope and tripod) Orion Catalogue

  33. Telescopes - Reflectors • 10 inch Reflector • Orion® Atlas 10 EQ • Light Grasp = 78.5 sq. inches • Focal length = 1200 mm • Weight = 117 pounds • (telescope and tripod) Orion Catalogue

  34. Telescopes – Reflectors • Dobsonian mounts were designed for larger reflectors that were too unstable on tripods. • They sit on the ground • Simple structures with Teflon bearings that provide smooth vertical/horizontal movement • Lighter than tripods Orion Catalogue

  35. Telescopes - Reflectors • 8 inch Reflector • Orion® SkyQuestTM XT8 IntelliScope® • Light Grasp = 50.2 sq. inches • Focal length = 1200 mm • Weight = 41.6 pounds • (telescope and tripod) Orion Catalogue

  36. Telescopes - Cassegrains • Cassegrains– have a compact tube which incorporates primary and secondary mirrors that fold the light path and focus the light into the eyepiece at the end of the tube. Orion Catalogue

  37. Telescopes - Cassegrains • Cassegrains(catadioptric) • Maksutov-Cassegrain • Schmidt-Cassegrain • Shorter and lighter than the others • Tend to be more expensive • Good for both astronomy and terrestrial viewing • Image is right side up but reversed left to right. Orion Catalogue

  38. UFO Telescope • Meade LX200R 12” • 305 mm (12 in.) • Advanced Ritchey-Chrétien optical design • Focal length = 3048 mm • Weight = 125 lbs. • (telescope and tripod) www.meade.com

  39. Telescopes – Eyepieces Your eye • An eyepiecebrings the light rays gathered by the telescope into sharp focus. • The eyepiece determines the magnification, as well as its brightness and contrast Orion Catalogue

  40. Telescopes – Eyepieces • Eyepieces with shorterfocal lengths (lower numbers) provide higher magnifications • Ex. 4 mm to 12 mm focal length • Images under high magnifications become more and more fuzzy, depending on the quality of the optics

  41. Telescopes – Eyepieces • Eyepieces with longerfocal lengths (larger numbers) provide lower magnification, but yield brighter, sharper images • Ex. 20 mm to 40 mm (wider angle)

  42. Telescopes – Eyepieces • Eyepieces • MediumLengths • 13 mm to 19 mm • The author recommends having at least one low (20-40 mm) and one medium (12-19 mm) power eyepiece.

  43. Calculating Magnification Magnification = Telescopefocal length Eyepiece focal length • Telescopefocal length = The distance from the center of a curved mirror or the center of the lens (where light passes through the first element of the telescope) to the focal point. Orion AstroView Meade LX200R Orion Catalogue

  44. Magnification = Telescope focal length Eyepiece focal length Eyepiece focal length = The distance from the center of the field lens (where light passes through the first element of the eyepiece) to the focal point. Given in millimeters ex. 25 mm, 14 mm, 7.5 mm) Calculating Magnification Orion Catalogue

  45. Magnification= Telescope focal length Eyepiece focal length Examples 750 mm = 30x (my telescope) 25 mm 3048 mm = 122x (12” Meade) 25 mm OR 750 mm = 100x (my telescope) 7.5mm 3048 mm = 406x (12” Meade) 7.5 mm Calculating Magnification

  46. Magnification = Telescope focal length Eyepiece focal length Eyepieces for Meade LX200R 12” 3048 mm = 117x 26 mm 3048 mm = 218x 14 mm Calculating Magnification

  47. Telescopes – Eye Relief • Eye Relief is the distance between your eye and the eyepiece lens, when the image is in focus • Eyeglass wearers need at least 15mm Orion Catalogue

  48. Telescopes – Eye Relief • Shorter focal-length eyepieces tend to have shorter eye relief than longer focal length eyepieces. • Smaller lens openings • You need to get closer to them to see the image • Like looking through a peek-hole. NightWatch, p. 76 17mm 6 mm Orion Catalogue

  49. Telescopes – Eye Relief • Eye Relief can be improved • Larger eyepiece lens openings to make it easier to see the image with your eye farther away • Much more comfortable viewing • These eyepieces will be more expensive 3.8mm 9.5mm Orion Catalogue

  50. Telescopes – Barlow lens • Barlow lensis a simple, relatively inexpensive lens which doubles or triples the magnifying power of a given lens. Orion Catalogue