Introduction
Week 5 will explore the design, concepts and use of telescopes.
- Observing has been the life-blood of astronomy since Galileo first turned his small telescope towards the skies, and observed sun-spots and some planets, showing for the very first time that there were imperfections in the heavens. He studied the satellites of Jupiter (the four bright Galilean satellites) from which the speed or velocity of light was later determined.
- Using some type of telescope becomes a must for anyone interested in astronomy, although it now would be possible to conduct many interesting observations using software and Internet images from professional facilities. We will describe in some detail the various telescope and mounting designs, the setting-up process and the need for a motor driven polar axis. Techniques for observing faint objects will be included, and we will study carefully how to safely project the solar image.
- Analysis is the recognition and evaluation of useful observations and often for this an accurate timing source is required. A short wave radio and tape recorder are favoured equipment to supplement a good telescopic observation so that you may obtain maximum value from your hobby. Finally we will touch on the analysis of your data by computer programming techniques so that you can see the value of original work in astronomy.
Sharing data: It is very important to make other astronomers in this country and overseas aware of your observations. I have therefore provided Internet links to the primary sites of appropriate establishments working in specific areas..
Telescope design
Activity: Here is a link concerning one of the newest amateur telescope designs, the Dobsonian which is an altitude-azimuth mounting (see Week 1):
http://zebu.uoregon.edu/~mbartels/scopes/scopes.html Try this link to robotic telescopes, some of which can be operated or used via an internet link: http://www.eia.brad.ac.uk/rti/automated.html
Telescope use
Activity: This a link shows the very wide range of telescopes commercially available from Celestron in the USA. Look at it to see the various types and designs available. (I have included this link for information not as an advertisement!
Telescope setting-up
This is a corner-stone of this course! Without a correctly set telescope observing can be at best very difficult if not impossible. Let us first deal with a moderately sized equatorial reflecting telescope, noting that the principles are the same for an equatorially mounted refractor.
We will start with the two illustrations of my small Newtonian equatorially mounted telescope to which I referred you in Week 3. Let us use these to guide you through the correct settings procedure. Firstly adjust the angle of the polar axis to suit your previously determined latitude. This is done by releasing the locking screw near the top of the tripod and setting the polar axis angle to your latitude as accurately as possible (in my case to 35 1/2 degrees) and then tightening the lock.
Next set the polar axis to point to the South Celestial Pole (SCP) by aligning the telescope tube to a magnetic compass set on level ground at the centre of the tripod. This can be a little tricky due to parallax with the tube well above the ground, but persevere until the alignment is the best achievable.
Once you are satisfied with these settings, make permanent marks on the level surface on which the instrument has been setup so that you may return quickly to this setting.
As a check on your SCP setting, we need to consult an ephemeris to find the time of solar transit for your location. At the time of transit (given here for the latter part of 1999 in local time for Canberra at longitude 149 degrees E) draw a chalk line on the level surface with a straight edged piece of timber to coincide with the shadow; this will point accurately to the SCP. Compare it with the magnetic heading previously used; they should indicate the SCP equally well, but some magnetic variation may apply at your location so use the solar transit as a preference.
Observing
At the beginning
You will probably do most, if not all, your observing at night, so at the beginning make this easier by setting up during daylight, your telescope on the markings made for the tripod, it will become second nature in the dark later after some practice. I recommend a torchlight, but you should be aware that this can upset your night vision.
When approaching the instrument, take your time as your eyes need to adjust to the darkness; To upset the telescope at the beginning of your observing session by bumping into it saps your confidence.
Start with an easily observed object such as the moon or Jupiter. Most telescopes are fitted with a small finder refractor telescope with cross-hairs, which can be pointed at the object sought. Move the main instrument in right ascension about the polar axis, and in declination about the declination axis after loosening the clamping screws on BOTH axes.
Look through the finder with (say) the right eye and bring the two images, the magnified one from the finder (right eye) and the naked eye image (left eye) to coincide. You should now have the required object in field of view of the main telescope, so carefully clamp the two axes and check in the eyepiece. If you do not see, slowly adjust each axis using their slow motion screws to centre the object in the finder cross-hairs and then, as required, in the eyepiece field of view of the main telescope.
The rotation of the earth will be very noticeable at high magnification, so slowly turn the polar axis adjusting screw to match this rotation. This will require a lot of practice AT FIRST, but it will become second nature as you become absorbed in your observing.
Advanced observing
If your telescope is fitted with setting circles, you can attempt more difficult objects. On the polar axis there is a circle showing right ascension (RA), or hour angle and on the declination axis, declination (Dec) in degrees.
The two axis setting circles need to be set on a star that can be easily seen, such as the Bayer named alpha1 centauri at RA (14h 39.5m) and Dec. (- 60 degrees 50 minutes). Once this double star has been located (it is the top star of the Pointers normally above the Southern Cross) check and adjust the setting circles to these coordinates. The coordinates of astronomical objects such as stars and nebulae are always the same for a particular epoch and once these coordinates are set, other objects can be dialled-in for easier location. The coordinates of objects of interest can be found from a CD-ROM, or a simple set of charts such as the Norton Star Atlas and Reference book (Mine is dated 1973, but there are later editions). It is good practice to check the coordinates before observing each night.
Other objects such as nebulae, Messier and NGC objects as well as some of the fainter planets, can be found using RA and Dec settings. Here again, practice makes perfect and observing with a telescope will be become a rewarding adventure if you use the principles outlined here.
Safe solar observing
Never, never look directly at the sun with your naked eyes, finder or main telescope. The heat from the sun will blind you in less than a second. Always see the sun via a projected image.
How to project an image of the sun
To locate the sun, always leave the dust cap on the finder, place a hand behind it and watch its shadow.
Move the telescope so that only a circular shadow is seen (and not an elongated cylinder).
Once this has been achieved, prepare a white projection disk and place this some distance (approximately 20 cm) from the main telescope eyepiece and normal to it.
Carefully focus the image of the sun onto this disk, and the projected image from the opposite side of the telescope. If others are present make sure they are NOT on the side where the disk is positioned so that nobody can try to look directly into the eyepiece.
The white projection disk can be conveniently supported back to the telescope to allow comfortable viewing of the image. On favourable days, sun spots can be seen and you might observe the transit of Mercury from 21h 18m (UT) on Monday 1999 November 15.
Remember great care is necessary, particularly in a group with children. - Guard the telescope every second while observing the sun's projected image.
Activity: Here is a good site to see the latest sun-spots observed in Hawaii
Analysis
This may take many forms, from very advanced, such as the prediction of Baily's Beads at a solar eclipse, down to the compilation of observations for the Occultation (ILOC) clearing house in Japan, or the submission of lunar eclipse crater timings to me at the Calwell Lunar Observatory for reduction and information feed back.
I started with DOS programs in 1984, and today have modified these to run on my Macintosh computer. There are many prediction suites of software commercially available, but the best satisfaction comes from writing your own. If you are interested in conducting your own analysis, please e-mail me for further guidance.
Questions for reflection
Use references to the notes and websites and see if you can answer the following questions. If you have any problems, e-mail me or put your query on the discussion page.
What are the main types of reflecting telescopes? (Hint: you should list and describe four).
How would you find the most interesting and most easily observed objects (the moon and Jupiter) with your telescope?
What is the importance of right ascension and declination when dialling-in objects?
How can you find the South Celestial Pole in the night sky?
How would you project an image of the sun with your telescope? What precautions would you take in doing this?
How would you find coordinate information for observing the planet Mars?
Activity
Continue your observations of a NGC or Messier galaxy (Week 4)
Messier objects can be observed in the night sky with a moderate telescope. See if you can find any of the Messier catalogued galaxies, or any of the NGC galaxies. If you have a CD-ROM planetarium, you can easily identify them and find their position in the night sky for your location.
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