What to do with a telescope in the summer?
The nights are shorter, and the only decent time is in the "middle of the night".Heading towards the "Longest Day", the time for decent observation is getting shorter and shorter.
The Sun spoils the view of the Moon and the stars.
So what to do?
Well, why not look at the Sun instead?
The Sun is VERY bright, and gives out quite a lot of UV radiation and IR (heat) radiation, as well as visible light.
The UV is bad for your eyes (UV can easily cause PERMANENT retinal damage), and the IR, as any child who has burnt paper using a magnifying glass will testify, can damage equipment and/or your eyes! - if it can burn paper, think what it can do to your eyes!
Clearly, some sort of filter is needed to go over the "end" of the telescope to cut down the light, remove the dangerous UV radiation, and reduce the IR (heat) radiation to an tolerable level.
Eyepiece filters can help, but they are not going to protect the insides of the 'scope from the IR.
So why not play it safe and get a large filter to go over the "end"?
First question is ... what size is the "end"?
Technical terms like aperture or indside diameter and outside diameter may be quoted for some common 'scopes, but you may have a dewshield or suchlike, so the actual filter size required may be more than the "listed" size.
For common telescopes like a Celestron etc., chances are a quick Google search will bring up an online telescope shop with filters for your telescope.
But what if you have something less common, like my TAL-120?
Time to get out the ruler, and get measuring ...
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| My TAL-120 telescope is about 140mm across the "open" end. |
But your 'scope (unless it is a similar model TAL-120) is likely to have a different size tube ("body"), as it depends on how thick the tube is, how much clearance there is between the mirror and the tube, and whether the tube has a wide ring at the end (mine does), or you are using a dewshield, and the filter is going over the end of that rather than the telescope tube (in that case just measure across the dewshield!)
After you know what size you want, you can go to an online shop like Green Witch (in the UK), who sell the excellent range of "Kendrick" Solar Filters, which have little locking screws to hold the filter on securely - you certainly don't want a gust of wind blowing the filter off when you are looking at the Sun !!!
Remember that the filter has to fit over the telescope, so the fit can't be too tight - my TAL-120 measures in at about 140mm, so I would have the choice of a Kendrick filter with a 130mm to 140mm size range, or (the next size filter up) one with a 139mm to 149mm size range.
With my measured telescope tube size of 139mm/140mm (approx), the "safe" option would be to buy the larger (139-149mm) size, and that would also allow me the option of fitting a "dewshield" at a later date, if I want.
The other alternative is to take your telescope to a "physical" astronomical shop, and discuss your needs with them.
The Kendrick filters use the excellent (and widely considered the safest for your eyes!) Baader Astro Solar film.
The Kendrick filter is not cheap (£76 in the UK, so that is about $120 in the US, and about 95 Euros), but, without wishing to be overly dramatic, how much are your eyes worth?
In another article in the future, I will show you how to buy a sheet of the same filter material (Baader Astro Solar), and make your own filter at home, but be sure you are careful, and follow the precautions, and you are confident you understand what you are doing - if you have any doubts, then buy a ready-made filter (other makes of solar filter are available, and most use the same Baader Astro Solar material, so if properly fitted will allow an equivalent image to be viewed/photographed, and with an equivalent degree of safety).
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