Star Gazing – Useful Information

Glossary and Useful Formulae

Magnification (Power) of telescope  = Focal length of telescope / Focal length of eyepiece

Focal Ratio (f/stop) = Focal length of telescope / Aperture of telescope mirror or lens
A “fast” speed (f/11, f/12 – f/15) is good for high power observing (moon, planets, splitting doubles)
A “slow” speed (f/4, f/5) is good for low power, wide-field observing (star fields, Andromeda nebula)
A “medium” speed (f/6 – f/10) is good for both types of observing

Actual or True Field of View  – How much of the sky the eyepiece can see when in the telescope = Apparent Field of View / Magnification of Eyepiece

Apparent Field of View – How much of the sky the eyepiece can see before it is fitted to the telescope

Exit Pupil (the narrowest point of the cone of light leaving your telescope) = Diameter of Primary Mirror / Magnification
The exit pupil should match or be less than the size of your pupil at night. For a 30-year old this is typically  7mm, reducing by 1mm per decade, so for a 60-year old, it will be 4mm. All figures are averages

Focal Length of Eyepiece – The distance between the lens and point of focus (focal plane). 

Eye Relief – How far your eye should be from the eyepiece to see all the field of view

Greek Alphabet

Order Character Symbol Excel Alt Code (Symbol)
1 Alpha α a ALT 97
2 Beta β b ALT 98
3 Gamma γ g ALT 103
4 Delta δ d ALT 100
5 Epsilon ε e ALT 101
6 Zeta ζ z ALT 122
7 Eta η h ALT 104
8 Theta θ q ALT 113
9 Iota Ι i ALT 105
10 Kappa κ k ALT 107
11 Lambda λ l ALT 108
12 Mu μ m ALT 109
13 Nu ν n ALT 110
14 Xi ξ x ALT 120
15 Omicron ο o ALT 111
16 Pi π p ALT 112
17 Rho ρ r ALT 114
18 Sigma σ s ALT 115
19 Tau τ t ALT 116
20 Upsilon υ u ALT 117
21 Phi φ j ALT 106
22 Chi χ c ALT 99
23 Psi ψ y ALT 121
24 Omega ω w ALT 119

Lessons Learnt

  1. Stellarium and SkEye are VERY impressive but I still love my 1971 Norton Atlas
  2. An Avon toiletries bag is a perfect place to hold eyepieces, lens caps and tools
  3. Feet are colder, backs are stiffer and bending over is harder in 2020 than in 1972
  4. Yoga teachers’ recommend a viewfinder without a right angle eye-piece
  5. A height adjustable chair is an essential accessory.
  6. Put thick walking socks on over a thinner pair at the start of observation periods
  7. Walking boots are better insulators than trainers and both transfer mud  outdoors<>indoors very efficiently
  8. Just because you can’t see mud in the dark does not mean that it is not there when you go indoors
  9. Your partner may not wish to see Venus at 6.45am
  10. Just because SkEye tells you that the Spindle Galaxy is visible from your location does not mean that you can find it on your first date with Dobo.
  11. Just because you can find Alkaid, does not mean you can find the Whirlpool Galaxy
  12. Up means down and left means right makes pointing difficult.
  13. Sometimes just looking though the eyepiece at a load of dim stars is wonderful especially when you think what those little dots actually are, how old they are and how far away they are!
  14. Patience is a good thing – M51 will still be there tomorrow (weather permitting)
  15. Plan what you want to see at least the night before
  16. Just because you can see Andromeda my moving your telescope in a different part of the garden, does not mean that moving your telescope is a good thing to do.
  17. In terms of easily finding things, my binoculars are better than my telescope 
  18. I need a finder scope on my finder scope!
  19. FLO are a nice company to deal with.
  20. You can find the ISS by “accident” without planning a view
  21. The amount of traffic on roads today compared to  45 years ago equates to the number of man-made objects that pass across your eyepiece
  22. The number of man-made objects that pass your eyepiece is alluring and frightening at the same time
  23. You do not need a hearing aid to Skywatch
  24. Learning star patterns (asterisms) helps you to find “difficult” objects
  25. Starting with M1 may not be the best / easiest way to start a Messier tick list  
  26. 8” is the Dobsonian sweet spot
  27. Doctors should prescribe star gazing to insomniacs
  28. Holding a phone to an eyepiece to capture the moon is like balancing a pencil on its flat end
  29. Holding a phone to an eyepiece to capture a planet is like balancing a pencil on its pointy end

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