stargazing 101 “stargazing equipment” chapter 5 september 22, 2009

Stargazing 101Stargazing 101““Stargazing Equipment”Stargazing Equipment”

Chapter 5Chapter 5

September 22, 2009September 22, 2009

What did you see this

past week?

September 2009www.OrionTelescope.com

Viewing the StarsViewing the Stars

1. Naked-eye viewing

2. Binoculars

3. Telescopes

Viewing the Stars – Viewing the Stars – Naked-Naked-eyeeye

1. 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 Star Brightness – Little DipperDipper

• 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

Kochab

Viewing the Stars – Viewing the Stars – BinocularsBinoculars

2. 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

BinocularsBinoculars • 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


• 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


• 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 – TypesBinoculars – 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 –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 – Binoculars – Roof Roof prismsprisms

• 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 Binoculars – lens coatingscoatings

• 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 binocularsHow 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 Novel ways to steady binocularsbinoculars

• The author recommends using: • A reclining lawn chair • A child-size inflatable dinghy

NightWatch, p. 62

Selecting binocularsSelecting binoculars• Some questions to consider when deciding on

particular binoculars: 1. How heavy are they, for their size?

2. Are they easy or awkward to use?

3. Are they difficult to focus?

4. Are objects at the edge of the field distractingly fuzzy, even though the center of the field is in focus?

5. And, the Bottom Line: How much do you want to spend?• Best to plan to spend around $100 or more

Selecting binocularsSelecting binoculars• “Binoculars under $100”

• Astronomy Magazine, April 2005

Viewing the StarsViewing the Stars –– TelescopesTelescopes

Orion Catalogue

3. Telescopes3. Telescopes

• Three distinct types of telescopic power

1. Collecting Power (also called light gathering power or light grasp)

2. Magnifying Power

3. Resolving Power

1. Collecting Power1. 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 most significant factor

Explorations: An Introduction to Astronomy, Thomas T. Arny, p. 155)

1. Collecting Power1. 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 Power2. 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 Power3. 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 Power3. Resolving Power

http://physics.uoregon.edu

Types of TelescopesTypes of Telescopes

• Three basic types of telescopes

1. Refractors

2. Reflectors

3. Cassegrains (catadioptric)• Maksutov-Cassegrain• Schmidt-Cassegrain

Telescopes - Telescopes - RefractorsRefractors1. 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 imageOrion Catalogue

How a lens focuses lightHow a lens focuses light

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


FocalPoint

Telescopes - Telescopes - RefractorsRefractors

• 60mm Refractor (2.4”)

• Meade model 285

• Light Grasp = 4.4 sq. inches• Focal length = 900mm

www.meade.com

Telescopes - Telescopes - ReflectorsReflectors2. 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 - Telescopes - ReflectorsReflectors2. 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 How a curved mirror focuses lightlight

• 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

Telescopes - Telescopes - ReflectorsReflectors

• 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


• 10 inch Reflector• Orion® Atlas 10 EQ

• Light Grasp = 78.5 sq. inches• Focal length = 1200 mm• Weight = 117 pounds


Orion Catalogue

Telescopes – RTelescopes – Reflectorseflectors

• 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


• 8 inch Reflector• Orion® SkyQuestTM XT8

IntelliScope®

• Light Grasp = 50.2 sq. inches

• Focal length = 1200 mm• Weight = 41.6 pounds


Orion Catalogue

Telescopes - Telescopes - CassegrainsCassegrains

3. 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 - Telescopes - CassegrainsCassegrains3. 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 TelescopeUFO Telescope

• Meade LX200R 12”• 305 mm (12 in.)

• Advanced Ritchey-Chrétien optical design

• Focal length = 3048 mm• Weight = 125 lbs.


www.meade.com

Telescopes – Telescopes – EyepiecesEyepieces

• An eyepiece brings the light rays gathered by the telescope into sharp focus.

• The eyepiece determines the magnification, as well as its brightness and contrast

Your eye

Orion Catalogue


• Eyepieces with shorter focal 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


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


• Eyepieces• Medium Lengths

• 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 Calculating MagnificationMagnification

Magnification = Telescope focal length Eyepiece focal length

• Telescope focal 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 Catalogue

Orion AstroView Meade LX200R

Calculating MagnificationCalculating MagnificationMagnification = 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)

Orion Catalogue

Calculating MagnificationCalculating MagnificationMagnification = 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 MagnificationCalculating Magnification

Magnification = Telescope focal length

Eyepiece focal length

Eyepieces for Meade LX200R 12”

3048 mm = 117x

26 mm

3048 mm = 218x

14 mm

Telescopes – Telescopes – Eye ReliefEye 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


• 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.

17mm 6 mm

NightWatch, p. 76

Orion Catalogue


• 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

Telescopes – Telescopes – Barlow lensBarlow lens

• Barlow lens is a simple, relatively inexpensive lens which doubles or triples the magnifying power of a given lens.

Orion Catalogue

Telescopes – Telescopes – Finder Finder scopesscopes

• 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 telescopeNightWatch, p. 67

Finder scopeEyepiece

Telescopes – Telescopes – Tripods/MountsTripods/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 – Telescopes – Tripods/MountsTripods/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

Mount

Tripod

Orion Catalogue

Telescopes – Telescopes – MountsMounts• 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

NightWatch, p. 67Orion Catalogue

AccessorieAccessoriess

• Electronic drive systems compensate for the rotation of the Earth and keep the image centered in the telescope

• Single axis and dual axis drives are available

www.meade.com

AccessoriesAccessories

• “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

www.meade.com

AccessoriesAccessories• 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 Telescope – lens coatingscoatings

• 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 Selecting TelescopesTelescopes

• 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 Selecting TelescopesTelescopes

• 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 ClockClear 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• http://www.cleardarksky.com

• Set for Dayton, Ohio or where ever you want• http://www.cleardarksky.com/c/Dayton_OHkey.html?1

AccuweatherAccuweather• “Satellite” view

• http://wwwa.accuweather.com/index-forecast.asp?partner=accuweather&traveler=0&zipcode=45409&u=1

• “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

WebsitesWebsites• Celestron Telescopes

• http://www.celestron.com/main.php• Meade Telescopes

• http://www.meade.com• Orion Telescopes and Binoculars

• http://www.telescope.com• Astronomy Picture of the Day

• http://antwrp.gsfc.nasa.gov/apod/astropix.html • Hubble Site

• http://hubblesite.org• NASA

• http://www.nasa.gov/home/index.html

Autumnal EquinoxAutumnal 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• StarDate.org (September 21, 2009) Track #46

Biology: Concepts and Connections, 5th ed. Benjamin Cummings

Autumnal EquinoxAutumnal Equinox

stargazing 101 “stargazing equipment” chapter 5 september 22, 2009

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