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Stargazing 101. “Stargazing Equipment” Chapter 5 September 22, 2009. What did you see this past week?. September 2009 Viewing the Stars. Naked-eye viewing Binoculars Telescopes. Viewing the Stars – Naked-eye. Naked-eye viewing is the best way to start

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stargazing 101

Stargazing 101

“Stargazing Equipment”

Chapter 5

September 22, 2009

What did you see this past week?

September 2009

viewing the stars
Viewing the Stars
  • Naked-eye viewing
  • Binoculars
  • Telescopes
viewing the stars naked eye
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
star brightness little dipper
Star Brightness – Little Dipper


  • 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

viewing the stars binoculars
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
  • 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
  • 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

  • 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

binoculars types
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.
binoculars porro prisms
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

binoculars roof prisms
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

binoculars lens coatings
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.
how to use binoculars
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
novel ways to steady binoculars
Novel ways to steady binoculars
  • The author recommends using:
    • A reclining lawn chair
    • A child-size inflatable dinghy

NightWatch, p. 62

selecting binoculars
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
selecting binoculars1
Selecting binoculars
  • “Binoculars under $100”
    • Astronomy Magazine, April 2005
3 telescopes
3. Telescopes
  • Three distinct types of telescopic power
  • Collecting Power (also called light gathering power or light grasp)
  • Magnifying Power
  • Resolving Power
1 collecting power
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)

1 collecting power1
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

2 magnifying power
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.
3 resolving power
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.
3 resolving power1
3. Resolving Power

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

how a lens focuses light
How a lens focuses light
  • A lens bends (or refracts) the light and focuses it on a point



Explorations: An Introduction to

Astronomy, Thomas T. Arny, p. 155)

telescopes refractors1
Telescopes - Refractors
  • 60mm Refractor(2.4”)
  • Meade model 285
  • Light Grasp = 4.4 sq. inches
  • Focal length = 900mm

telescopes reflectors
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

telescopes reflectors1
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

how a curved mirror focuses light
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



Explorations: An Introduction to

Astronomy, Thomas T. Arny, p. 158)

telescopes reflectors2
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

telescopes reflectors3
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

telescopes r eflectors
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

telescopes reflectors4
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

telescopes cassegrains
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

telescopes cassegrains1
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

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

telescopes eyepieces
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

telescopes eyepieces1
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
telescopes eyepieces2
Telescopes – Eyepieces
  • Eyepieces with longerfocal lengths (larger numbers) provide lower magnification, but yield brighter, sharper images
    • Ex. 20 mm to 40 mm (wider angle)
telescopes eyepieces3
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.
calculating magnification
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

calculating magnification1
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

calculating magnification2
Magnification= Telescope focal length

Eyepiece focal length


750 mm = 30x (my telescope)

25 mm

3048 mm = 122x (12” Meade)

25 mm


750 mm = 100x (my telescope)


3048 mm = 406x (12” Meade)

7.5 mm

Calculating Magnification
calculating magnification3
Magnification = Telescope focal length

Eyepiece focal length

Eyepieces for Meade LX200R 12”

3048 mm = 117x

26 mm

3048 mm = 218x

14 mm

Calculating Magnification
telescopes eye relief
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

telescopes eye relief1
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


6 mm

Orion Catalogue

telescopes eye relief2
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



Orion Catalogue

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

Orion Catalogue

telescopes finder scopes
Telescopes – Finder scopes


Finder scope

  • Finder scopes are miniature telescopes mounted parallel to the main tube that allow easy alignment of the target object.
  • Object is centered in the crosshairs of finder scope
    • Has to be adjusted to the main telescope

NightWatch, p. 67

telescopes tripods mounts
Telescopes – Tripods/Mounts
  • A sturdy tripod and mount are essential to jiggle-free viewing
    • Especially at higher magnifications
      • The slightest movement is greatly magnified
  • The mount also has to be able to smoothly adjust for the Earth’s rotation
    • Especially at higher magnifications
      • The objects move quickly through the field of view
telescopes tripods mounts1
Telescopes – Tripods/Mounts

Altazimuth Mount

Up and down (altitude), and left and right (azimuth – around the horizon) rotation controls

This model has slow- movement cable controls

Least expensive



Orion Catalogue

telescopes mounts
Telescopes – Mounts
  • Equatorial Mount
    • The polar axis on the mount is aligned toward Polaris
      • Then you only have to turn a single knob to compensate for the Earth’s rotation

Orion Catalogue

NightWatch, p. 67

  • Electronic drive systemscompensate for the rotation of the Earth and keep the image centered in the telescope
  • Single axis and dual axis drives are available

  • “Go to” computer controllers
    • A computer is built into the telescope base
    • Once the computer is aligned, the system is able to find thousands of celestial objects
      • Ex. Meade AutoStar II – has a 145,000 celestial object database

  • Filters
    • Moon – too bright when more than half the moon is lighted
    • Planets – different colors enhance the image
    • Sun – large filter that goes over the front opening
      • Otherwise, you could “cook” the inside of the telescope

Orion Catalogue

telescope lens coatings
Telescope – lens coatings
  • Anti-reflection lens coatings produce much better images
    • Increase light transmission through lens
    • Reduce internal reflections
    • Meade Ultra-High Transmission Coatings (UHTC)
      • Increases brightness by nearly 20% over their other lens coatings
selecting telescopes
Selecting Telescopes
  • How much do you have to spend?
    • The author says that if you can not spend at least $300, your best bet is to buy a good pair of binoculars and wait until you have more money to spend on a telescope
      • So you don’t get the ”Trash-Scope Blues” (p. 65)
selecting telescopes1
Selecting Telescopes
  • The author has good comments:
    • “Telescope comparisons” (p. 80)
    • “Factors to consider when selecting a first telescope” (p. 81)
    • “Trash-Scope Blues” (p.65)
clear sky clock
Clear Sky Clock
  • Transparency = total transparency of the atmosphere from ground to space
    • Calculated from the total amount of water vapor in the air
  • Seeing = being able to see fine detail at high magnifications
    • Bad seeing is caused by turbulence, combined with temperature differences in the atmosphere
      • Set for Dayton, Ohio or where ever you want
  • “Satellite” view
    • “Map in motion” to see how the clouds are moving
    • Can see if clouds are present and if they will be moving in or out
  • Celestron Telescopes
  • Meade Telescopes
  • Orion Telescopes and Binoculars
  • Astronomy Picture of the Day
  • Hubble Site
  • NASA
autumnal equinox
Autumnal Equinox
  • The Autumnal Equinox occurred earlier today, September 22, 5:18 pm (EDT)
    • “When the Sun crosses the equator heading south for the year. This event marks the start of Fall in the northern hemisphere.” (StarDate Magazine, January/February 2007)
    • The length of day and night are the same (almost – Sunrise 7:24 am, Sunset 7:33 pm)
      • Why?
    • The Sun rises due the east and sets due west
      • (September 21, 2009) Track #46
autumnal equinox1
Autumnal Equinox

Biology: Concepts and Connections, 5th ed.

Benjamin Cummings