Only Mars (and Mercury, in theory) have a visible surface

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Planetary Observing

• Presented by John Bishop
• June 2007

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This Talk

• Focused on visual observing only
• No planetary mechanics (go to ST for whats up
  tonight)
• Lots of how-tos
• Some equipment considerations
• Theres also a human side

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Planets Are Different!

• Small
• Bright
• Detailed
• Individual

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Planets are Small

• Neptune is 2 arc-seconds Venus can be almost 60
  arc-seconds during a transit but thats still
  quite small!
• Small means you need to magnify
• Small means seeing is very important
• Small means smoothness (quality) of optics is
  important

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How Much To Magnify?

• Atmosphere limits us to about one arc-second
  seeing image blur pixels are thus about one
  arc-second dots
• Our eyes have pixels that are about one
  arc-minute dots
• The minimum magnification to see all the detail
  is thus about 60x.
• But theres more!

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More on Magnification

• Use changes in magnification to
• Adjust the brightness to a comfortable level
• Change the visibility of colors (more later)
• Change the contrast (more later)
• Tease out more detail by matching the pixels of
  the contrast to your eye pixels
• Prepare your image for the lucky instant of
  good seeing

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Magnification and Tracking

• Magnification magnifies Earths rotation as well
• You can hand-track at 300x but then you cant
  do anything else!
• Tracking is a huge help
• Equatorial mount
• Tracking table
• If you cant track, use a lower magnification

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Planets Are Bright

• Magnitude 8 to -4 (Venus is the third brightest
  natural thing in the sky!)
• Dont need to gather lots of light
• Glare (too much light) can be a problem
• Color sensed varies by light level
• Too much or too little washes out color
• Good news brightness permits the use of filters

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Planets Are Detailed

• They have details going way below 1 arc-second
• They have color and brightness variations
• They have high-contrast and low-contrast features
• Only Mars (and Mercury, in theory) have a visible
  surface Jupiter has long-lasting cloud features
  Saturn has ring features
• They can be oblate Venus and Mercury can be
  crescents

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Color and Colored filters

• Colored filters can increase contrast at the cost
  of dimming (use lower magnification)
• Named by Wratten numbers (A)
• Light filters are better than dark ones were
  after subtle effects, not mood lighting
• Dark filters require a bright image (big aperture
  and/or low magnification)
• There are special Planetary Contrast filters I
  havent tried them
• Try any you have!

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The Filters I Use Most Often

• light yellow (8)
• light blue (82)
• magenta (30, Minus Green hard to find, worth
  finding)
• orange (21)
• nebula (e.g., DGM VHT, good on Mars if you dont
  have magenta)
• neutral (Moon filter)

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Filters I Have And Dont Use

• Green (56)
• Dark Blue (80)
• Red (25)
• Dark Yellow (12 Minus Blue)
• Violet (47)

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Filters Which Might Be Useful

• Yellow-Green (11)
• Light Amber or Salmon Pink (85)
• Planetary Contrast
• Mars BandMates, Mars A, Mars B
• O-III
• H-a
• H-ß

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Filters I Cant Find

• Minus Yellow Cyan (?)
• Minus Red Blue-green (44)

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Planets Are Individual

• Each planet is different and should be treated
  differently
• Some are very rewarding to observe, some are not
• They have history and a connection to myth
• They are well-placed or otherwise!

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Rewarding Planets

• The rewarding ones are also the big
  crowd-pleasers at sky-watches
• Mars the winner for those who like science
  fiction
• Jupiter the winner for those who like moons
• Saturn the winner for those who like rings

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The Planet Mars

• Varies in apparent size up to 27 arc-seconds
• Good apparitions about every 2 years
• Lots of surface detail (and its a real surface!)
• Cool names (Syrtis Major, etc.)
• Ice cap, clouds vary from day to day
• Sandstorms

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Mars Observing How-to

• Yellow, orange or red filters bring out dark
  areas
• Neutral can bring out Hellas basis
• Blue can bring out cloud details
• Magenta filters are great close to natural
  color and greater contrast of dark areas!
• Nebula filter exaggerates colors, makes a bit
  blurry
• Check ice cap edge varies as melting happens
• Rotates at near-Earth rate so youll see the
  same side night after night
• Responds well to changing magnification

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The Planet Jupiter

• Huge 40 to 44 arc-seconds
• Many different colors (blue, brown, white, pink)
• Lots of cloud detail, to limit of resolution
• Rotates very fast changes as you watch
• Visibly oblate
• Moons add interest

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Jupiter Observing How-to

• Try all your color filters!
• Try varying magnification
• Two big dark bands look for detail beyond them
• Zones (white stripes)
• Thinner bands (dark lines)
• Spots (in zones and bands)
• Festoons (diagonal stripes or interrupted lines)
• Barges (next level down of detail, I think)
• Great Red Spot is a Pale Pink Spot these
  days look for Red Jr.

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Jupiters Moons

• Move while you watch
• Moon goes behind Jupiter occultation
• Moon goes into Jupiters shadow eclipse
• Moon in front of Jupiter transit (hard to see)
• Moons shadow on Jupiter shadow transit
  (dramatic)

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Observing Saturn

• Everyone loves the rings use yellow filter to
  bring out Cassinis Division
• Use blue filter to emphasize ring details
• 1 to 6 moons visible the inner ones move while
  you watch
• Planet has subtle banding (use yellow and blue
  filters)

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Not-so-Rewarding Planets

• Mercury
• Venus
• Uranus
• Neptune
• The rest

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Observing Mercury

• Has phases
• Always close to sun and thus usually near horizon
  can use Horizon Wedge to see without color
  blur
• No easily-visible surface detail (like highlands
  of Moon all craters)
• Old guys thought they saw features and timed
  Mercurys rotation they were wrong!

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Horizon Wedges

• Atmosphere acts like a prism near the horizon
  (atmospheric dispersion)
• You can get 2- or 4-degree prisms to compensate
  for atmospheric dispersion
• Get the 2-degree prism if you want 4-degrees of
  correction, get two of them
• Require lots of back-focus may need Barlow-ing
  to achieve focus
• Big improvement, but cant completely compensate
  for dispersion
• Really only good for Mercury or sky-watches when
  you want to show a planet and the only one around
  is low

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Observing Venus

• Has phases
• Very large at times good in small scopes
• Usually no surface detail -- violet filters are
  said to show cloud detail

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Observing Uranus

• No detail visible in 4 arc-second disc
• Gorgeous bright yellow-green or green
• Obvious, non-stellar color
• Titania is mag 14, visible in very large
  telescopes

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Observing Neptune

• No detail visible in 2 arc-second disc
• Dark blue edge indistinct due to limb darkening
• Greener in big telescopes
• Obvious, non-stellar color
• Triton visible in larger scopes, mag 13.6

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Observing the Rest

• Mostly you look at these just to say you saw them
• Pluto just a mag 13 dot
• Asteriods brighter dots
• Galilean Moons 1 arc-second discs but bright
  people have seen detail on Ganymede

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The Ideal Planetary Telescope

• Right eyepieces simple, narrow-angle
• Right focal length long, f/big
• Right aperture small
• Right design unobstructed, driven
• The old guys werent so dumb after all!

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The Right Eyepieces

• You want non-coloring, contrast-saving designs
• Small number of surfaces is best (less
  scattering)
• Some edge distortion is ok
• Wide angles are definitely not needed
• Most eyepiece designs work best between 10 mm and
  20 mm
• Barlows remove contrast you want single
  eyepieces if possible
• Orthoscopics and Monocentrics are the classic
  choices Plossls ok

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The Right Focal Length

• You want powers between 60x and 300x
• 300x with a 10 mm eyepiece means a focal length
  of 3000 mm 60x with a 20 mm means a focal length
  of 1200 mm
• You have to make some compromises
• The ideal focal length is at least 1500 mm 2000
  mm is better.

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The Right Aperture

• You dont need lots of light-gathering
• You want resolution, but the maximum the sky
  supports is about 1 arc-second
• 4 inches gives 1 arc-second resolution, 8 gives ½
  arc-second
• Larger apertures may have more seeing issues
• Larger apertures are hard to make high-quality
• The ideal aperture is thus a bit over 4 inches 5
  or 6 is great, 8 maybe too much of a good thing.

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The Right Design

• Obstructions rob contrast
• Under 15 not too bad planetary-optimized
  Newtonians
• Maksutovs and SCTs are losers here (30 or more)
• Refractors are good if they are long enough
• Long focal lengths (4-inch f/10, 6-inch f/20)
  mean that achromats will have almost no color
  error superior correction of apochromats not
  needed short apo-s not long enough
• Unobstructed reflectors have no color problems at
  all
• Off-axis Newtonian
• Schiefspieglers
• Yolos
• Even-more exotic designs exist (tetra-schiefs...)
• Schupman medials are great (ATMOB has one)
• Mounting and tracking a long scope is an issue

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If Your Scope Isnt Perfect

• Non-planetary Newtonian
• Short-focus apochromat
• Short-focus achromat
• SCT or Maksutov

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Newtonians

• Use high and low magnifications
• Try an off-axis mask on 12-inch or bigger
• Hole should be a convex shape
• Position between spider vanes
• Re-collimate telescope for best results
• Collimate normally
• Add mask
• Re-center secondary to point to off-axis section
• Re-collimate primary with star collimation

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Short-focus Apochromat

• Use Barlow or Powermate to get higher
  magnifications
• Learn to see details at low magnifications

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Short-focus Achromat

• Use Barlow or Powermate to get higher
  magnifications
• Use anti-violet filters to eliminate color
  fringes at higher powers
• Better get used to the color-error and train
  yourself to see past it.
• Consider a mask (90, 80)
• Raises f-number
• Reduces color error

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Achromat Example

• Rule of thumb is for an N-inch achromat to have
  minimal color error, it should be f/3N
• Orion 120 mm f/8.3 has a 1000 mm focal length
• A 110 mm mask produces a 4.3-inch f/9
• A 100 mm mask produces a 4-inch f/10
• A 92 mm mask produces a 3.6 f/10.8 (fits the
  rule)
• Trade color error for brightness and resolution

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SCT Or Maksutov

• Use very high or very low magnifications to put
  the contrast frequency of interest in the sweet
  spot (rapid variation)
• Aperture will compensate somewhat for obstruction

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The Human Side

• Your eye is not a camera and your brain is very
  involved with perception
• Your perception can be trained the more you
  know, the more youll see
• You can accumulate perceptions (even if you cant
  accumulate photons)
• If you just look, you wont observe engage your
  mind
• Therefore

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Draw What You See

• Accumulates transitory details
• Even one flash of detail is probably real
• Accumulates information from all magnifications
  and filters
• Forces you to really see details (a blob vs. a
  one-tenth diameter dot two-thirds of the way out
  from the center towards 2 oclock)
• Gives you a permanent record to show other people

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How to Draw Planets

• Make a circle 2-inches or more in diameter
  beforehand
• Sketch in details with pencil as you observe
• Talk to yourself and take notes
• Use a dim red light to guide your drawing note
  color with labels
• Have a solid base for the paper tape down so
  wind doesnt move it
• Finish or copy afterwards using ink and colored
  pencils

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Notes on Saturn banding
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Pencil Sketch of Saturn (31 March 2007)
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Mars Rough Sketch (26 Sept 2005)
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Mars, based on sketch
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Mars, 7 Nov 2005