Hi Ricci, Enchilada & All,
Quote:
Originally Posted by Enchilada
IMPORTANT CAUTIONARY NOTE
I would honestly suggest visual observation near the sun during daylight is very dangerous without adequate shielding from the sun's ray.
(Between about the 12th March to 6th April,
unless you are experienced, NO ONE SHOULD TRY IT!)
If you REALLY WANT TO DO IT, use an eye patch to stop glimpsing the sun as its brightness. Sunlight a bedazzling effect that stops you seeing very much let alone the crescent Venus - probably buggers up your deep-sky observing if you do it too long!
Also try and place the telescope in the shadow of a building, where it is impossible to point the optics at the Sun.
|
Ricci, don't take this as a criticism in any way but more a matter of adding a proper caveat to observing Venus when it is so close to the Sun. This is, as Enchilada has rightly pointed out,
very,
very important!
I robustly endorse Enchilada's comment/caveat. This should only be attemted by people who are very experienced and understand the proper precautions -- and take those proper precautions.
The only way I'd be doing it is by putting something like a building between the Sun and the 'scope so the 'scope is in the shade while the planet is visible. An accurately aligned GOTO 'scope is also a big advantage -- but still make sure the Sun is behind the building!
Now, I observed Venus on 5 June 2004 (approx 70 hours before the transit on 8 June 2004 and had also done so the few days before that. In this case I was using the 40cm Schmidt Cassegrain at Sydney Observatory (linked to The Sky v6.0) which I had very carefully aligned (to within a couple of arc-mins) with 2 stars (yep, in daylight -- it can be done). Venus was 4.8 degrees from the Sun at the time. I rotated the dome so that *most* of the 'scope was in the shade of the dome, but positioned so that it was impossible for the Sun to be able to pass right through the optical train of the telescope.
Here is a reproduction of what I posted on the AMASTRO mailing list that evening regarding the observation:
Just thought I'd report an observation of Venus made this afternoon with the 0.40m S/C at Sydney Observatory.
At 05:30 hrs U.T on 5 June (3.30pm local time), Venus was still detectable, now just slightly < 3 days before the transit. It was very difficult to see in the field at about 140x, because of the glare from the light of the Sun scattered in the atmosphere and in the dust of the optics. It was not visible in the 50mm finder at all. Not visible to the naked eye. Even in the main 'scope the field was incredibly bright, much worse than a full moon, and it took 15+ seconds to pick it up.
Indeed after locating Venus and the 10 mins of viewing, I walked past the front end of the 'scope and was quite alarmed to see that off axis light from the Sun was illuminating a brilliant 'doughnut' on the corrector plate after first being reflected off the primary mirror
However, time at the eyepiece was rewarding, the crescent is easily seen
stretching about 270 - 300 degrees around the disc, and I almost had the
impression from time to time, like Brian, that you could make out the full
circle, but I'm not willing to put the house on it. One of the staff at Sydney
Obs took a pic with a digital camera using the afocal method and we were
surprised to see it came out pretty well.
Venus was 0.38% illuminated from our angle at the time of observation. I don't know whether anyone can see it any closer to transit time (anyone out there like to have a go?)
Weather prospects for observing the transit from Sydney are pretty favorable for Tue afternoon. Basically pretty clear with some broken cloud is predicted.
Best wishes for good weather to you all, so we can all tick this one off the
list of things to see."
Just had a look through a few of the subsequent posts of others, Tom Polakis saw it the following evening (US time) but that was it. Please bear in mind that the membership of the AMASTRO list are almost without exception very, very experienced amateurs.
On a highly related issue, around the start of this decade I remember an article by a prominent writer/editor of a widely circulated (unnamed here), overseas-based astro magazine (it wasn't S&T) who wrote in his column about observing Venus in daylight. The advice that person gave was so casual and frankly glib in nature it
really got me steamed up. What was written amounted to
something like:
"work out how far Venus is from the Sun, measure it out by handspan or fingerspan and then look at that spot through the binoculars and if its not immediately visible, waggle them about a bit."
When I read that ... I saw
red! Dashed off a letter to the editor (which surprisingly was reproduced in full) and the columnist "modified" his advice in reply with a proper caveat. How the original column/comment made it through the proofreaders/editors and lawyers unscathed is anyone's guess.
Observing with a 'scope or binoculars near the Sun is very, very dangerous: Only for the very experienced and the very cautious.
As Frank Spencer's flying instructor (Some Mothers do 'av 'em") told Frank during his first lesson:
"There are old pilots, and there are bold pilots ... but there are no old, bold pilots."
You've only got one set of eyes after all ...
Best,
Les D
Important Cautionary Note
