RE: Transit of the sun. RE: SAFE SOLAR VIEWING

From: MALEY, PAUL D. (JSC-DO511) (USA) (
Date: Mon Apr 22 2002 - 08:11:55 EDT

  • Next message: Ed Davies: "Re: Transit of the sun. RE: SAFE SOLAR VIEWING"

    I want to add my concurrence to Dave's warning as someone who has been to 25
    solar eclipses as well as attempted to view satellites transiting the sun. I
    always construct an eclipse safety briefing with strong words of caution to
    eclipse observers in order to minimize any possibility that someone could
    suffer eye damage as a result of not having correct advice. The human eye
    can tolerate a lot before experiencing injury and since the cornea has no
    pain sensors, a person would not be aware of anything until long after the
    damage is done. Making a homemade solar filter is not a wise thing to do.
    Since ISS transits of the sun are perhaps going to be more widely publicized
    as ISS grows larger in size structurally, SEESAT should be diligent in
    providing the best eye safety advice in connection with this level of
    hobbyist interest.
    Use of any "sunglasses material" in any part of the optical chain is
    potentially dangerous to anyone attempting to view satellites during the
    day. Note also that the problem with mylar when bought in the form of solar
    blanket or thin film available in rolls is that you cannot always be sure
    you have the correct density, hence the bright field of view that often
    results when viewing after the material (one or two layers) is placed IN
    FRONT OF the telescope objective. I capitalize "IN FRONT OF" because some
    people have actually used mylar between the eye and eyepiece--an inherently
    dangerous practice also.  The mylar itself normally provides good protection
    assuming 1) it is used correctly in the optical chain, 2) it has no
    pinholes, 3) it is of the correct density.
    However, when the observer can easily detect that the field is 'bright', the
    thickness of the mylar is not high enough or there is light leaking
    somewhere around the mylar and being scattered inside the telescope. I don't
    think it was intentioned to say that sunglasses were OK to use, and that
    Ralph was just trying to dim the background after already using mylar to get
    it to a comfortable level. But the mere mention of using sunglass material
    may give some novice readers the erroneous impression that it is a safe
    I propose that there should be a standard rule in daytime satellite
    observation that states: "Warning: Observing satellites transiting the sun
    SHOULD NEVER BE ATTEMPTED unless the observer utilizes a neutral density 5.0
    filter placed IN FRONT OF the telescope objective." Perhaps such a warning
    ought to be placed on the SEESAT web page.
    As R.Chou points out in his advice to eclipse observers, there are a variety
    of bizarre materials that people have used to view the sun durign eclipses
    such as black and white/color exposed photographic film, CD's, smoked glass,
    the small green sun filters that often come with cheap telescopes that are
    screwed onto the back of an eyepiece (extreme danger here!), sunglasses,
    aluminum foil, clouds, reflections from a pail of water, etc. All of these
    are potentially dangerous and must never be used even if there is a marginal
    possibility that eye damage might be incurred. There are two other similar
    safe sun viewing methods that are not applicable for satellite viewing: 1)
    pinhole camera; 2) eyepiece projection onto a white screen.
    Paul D. Maley
    Tel. 281.244.0208, Fax. 281.244.1140
    Lat. 29.6049N, Lon. 95.1069W, Alt. 6m
    -----Original Message-----
    From: []
    Sent: Sunday, April 21, 2002 1:25 PM
    Subject: Was: Transit of the sun. RE: SAFE SOLAR VIEWING
    In a message dated 4/20/02 1:52:22 PM Mountain Daylight Time, writes:
    << About 30 minutes before the transit I set off with a Meade ETX-90
     with a doubled-over piece of silverized Mylar over the front for a solar
     filter . . .  One other problem was that the sun was
     still a little too bright in the scope, but I solved that problem by making
     a poor-man's neutral density filter by holding a pair of clip-on sunglasses
     between my eye and the ocular. >>
    Ralph --
    I got chills reading this.  I hope no one else attempts to watch a solar 
    transit with a homebrew Mylar filter like this.  Your eye is telling you 
    something, I think, if there is too much light to view in comfort.  Even if 
    you are comfortable with a homemade filter, you can damage your eye and feel
    no pain, if IR and UV are excessive, as they easily could have been.  
    Eyepiece mounted solar filters, exposed photographic film, smoked glass, 
    pieces of compact disk, foil-coated wrappers: all are inappropriate in a 
    solar telescope.
    Please spend the nominal $ to obtain a safe solar filter with a securely 
    attached cell, and spare yourself the risk of of a scotoma in the middle of 
    your visual field.
    Baader Astro-Solar film is inexpensive, available in sheets or mounted, and 
    gives a solar image markedly superior to typical glass and Mylar filters.
    view of sunspot detail and solar granulation markedly improved when I 
    switched to the Baader film from a US-made glass unit.  The sharpness and 
    contrast are much better, and the color is neutral.
    In the US, it can be obtained from Astro-Physics;  Jim Kendrick in Canada 
    supplies it in cells.  Perhaps Markus Ludes carries it Germany, or can 
    recommend a source.
    Dan Laszlo
    Fort Collins CO
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