Telescopes – Solstice Seasonings

Telescopes – Winter Solstice Seasonings

by Pat Browne

Winter solstice marks our Northern Hemisphere’s  shortest day and longest night of the year, when the sun’s daily maximum elevation in the sky is the lowest .You can see this effect during these days,  on a clear evening when the occasional cloud is illuminated by the low sun setting not long after 4PM,  very closely hugging a south-westerly horizon. The motion of the Sun our Star as reflected in our axial tilt making the position and motion of the closest star to us, the Sun vary throughout the year as follows

 

sunpaths

Information courtesy http://www.astronomynotes.com/nakedeye/s5.htm

The US Naval Observatory says winter solstice 2013 is at Dec 21 17:11  UT, and the Royal Greenwich Observatory concurs. That would be 5 hours earlier,  12:11pm EST (Local time). During this solstice season,  a telescope may “present” itself. If this occurs, you will want to be know how to use this tool  while the sun remains below the horizon for a longer period of time . So…

What is a Telescope?

• A tool to help see things that appear very dim and/or very small.
• Telescopes perform two basic functions:
1. Collect light (much more than your eye). This is the stuff emitted by celestial objects – moon, planets stars, star clusters, galaxies
2. Focus the light into an image we can see . The image represents photons emitted hundreds to thousands to millions of light years ago.
• Three main types you are likely to encounter:

1. Refractor

refractorTelescope2. Reflector

reflectorTelescope3. Compound Reflector

compoundReflector

Eyepieces for Visual Observing

Amateur astronomers have a choice of how they use the telescope to gather the light.

  1. They can look through an eyepiece into the telescope – this is called visual observing. The ratio between the focal length of the eyepiece
  2. They can capture the light using a camera (normally a digital camera although it used to be using special film emulsions).

For Visual observing, the choice of eyepiece is important. Most people think that the ‘strength’ or power of the telescope lies in its magnification. In fact, this is not really true in practice. With a sufficiently dark sky and dark adapted observer (you must allow your eyes to adjust to their night-time vision) you can observe deep sky objects in a telescope field of view with only 50x magniciation. 

For example, the little StarGazer Steve red scope that we use at our Night Sky Course Night Sky Course Observing Sessions (April 2014) is a 6″ aperture (primary mirror) and a focal length multiplier of 8.  48″ focal length is 1200 mm. It is roughly the length of the tube assembly. So for a given eyepiece we measure: For a wide field view we used a 24mm eyepiece:

Magnification = Focal Length Primary Mirror/ Focal Length Eye Piece

                                                                  Magnification = 1200 mm / 24 mm  = 50X

The most pleasing view in this scope is the eyepiece designed for this scope which is 18mm i.e. 4/3 or 66X Wide fields are ‘rich fields’. We can take in more of the cluster or more than 1 galaxy if we are looking at clusters. To do close-up work,to split doubles, or look at the detail on the planet – that’s when we want higher power! For this we would use 8mm (150) or smaller.

telescope-eyepiece4 eyepiece

For more information you can get lots of help from the Royal Astronomical Society of Canada . There are clubs in each province: for example – http://calgary.rasc.ca/telescopes/

Mounting Platform

Because we live on a platform that rotates 1 revolution in roughly 24 hours, objects that are closer to earth such as the planets, will not stay fixed in your field of view, For observing visually (meaning looking through an eyepiece into the telescope) this is not a big problem. If you walk away from the scope, you will need to re-center the object – this helps keep you aware of the sidereal rate of the earth’s turning – roughly 15 seconds of arc in the sky per second!

Telescopes are mounted on platforms called ‘telescope mounts’. Your telescope will probably be mounted on one of the following:

  1. Altitude=Azimuth mounts.
  2. Dobsonian mounts (for simple reflectors)
  3. Equatorial mounts

telescopeMounts

When the equatorial mount is properly aligned such that the Right Ascension axis is aligned with the North Celestial Pole, then the Declination axis is aligned with the Celestial Equator.

Celestial-Equator-Plane_300

Coutesy: http://www.astronomysource.com/tag/german-equatorial-mount/

 

When we have aligned the mount exactly with the polar axis, we have calibrated the mount’s celestial equator as well. The celestial equator is always orthogonal (right angle) to the polar axis. This mount is most suitable to be motor driven for tracking objects in the sky.To learn how to align equatorial mounts, here is an excellent resource: Polar Alignment Tutorial

Visual Observing with a Telescope – What to Expect

If you have never really looked through a telescope

  • at the Moon
  • at a Binary star system
  • at a nebula star or star system
  • at the larger planets
    • Saturn
    • Jupiter
  • at a Galaxy
    • or at a star cluster
    • or at a group of galaxies

OR If you have never really looked through a pair of binoculars

  • at the Pleaides
  • at a comet
  • at a colourful optical binary star system

You may not know what to expect or even where to look, or how to look!  If you are focusing on visual astronomy it will be best to come out and observe with other people and get a feel for what to see and how to look. One thing is for certain; what you see in the eyepiece is not what you see in photographs. The photons coursing through your optical path and tickling your retina came a very long distance to trigger your imagination!

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