From: "Terrence R. Redding, Ph.D." <tredding@mac.com>
Date: October 4, 2009 4:22:57 PM MDT
To: Steve Welch <swelch@complex.org>
Cc: Derek Breit <breit_ideas@hotmail.com>, Becky Ramotowski <beckster@cotse.net>, Pete Eschman <eschman@unm.edu>, David Dunham <dunham@starpower.net>, palmbeachastro@yahoogroups.com, "iotAoccultations@yahoogroups.com" <IOTAoccultations@yahoogroups.com>, macastronomer@yahoogroups.com, astro_IIDC@yahoogroups.com
Subject: Re: [TAAS-L] telescope needs for lcross
Steve, yes, I am following the various discussion on the subject of observing the LCROSS event.
I am copying all with my reply to you, and adding your hometown astronomy club here in the Palm Beaches, and a couple of Mac computer groups that have expressed an interest in either visually observing the event, or video taping the event.
As we move into the fall here in the Palm Beaches of Florida our skies are becoming more transparent. Just before sun rise I am seeing mag 4 skies from my back yard. Surprising really, and so I am expecting to have a good shot at imaging the event. I will do it with three scopes aligned with each other. The 14" will be high power on the target crater using a IR cutoff filter and a Tele Vue Powermate 2.5 feeding a WAT-120N+ camera, the Vixen ED80sf will use a Tele Vue Powermate 5.0X and another WAT-120N+, and the Stellarvue will be a prime focus with a Watec 902H2 Ultimate.
After the mutual event tonight I may play with the configuration to see whether I should adjust the optical paths. But that is my current thinking.
I have not identified a good source for a polarizing filter and would enjoy hearing recommendations on the score. I was out yesterday at about 7:30 AM to see if the sky would cooperate. It is very light at that time. While the observatory is in the shadow of the house, my block runs east west and at 3 degrees, the sun is already shining direct sunlight down my block.
I would encourage all copied here to read Steve Welches detailed message below on his plans for observing LCROSS and especially his analysis of how viewable this event is going to be in even modest telescopes.
Terry - W6LMJ - 14.287
Terrence R. Redding, Ph.D.
Redding Observatory South, West Palm Beach, Florida
http://olt.net/learningstyle/Site_2/Learning_Style_Research.html
How do amateur astronomers learn?
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Observers (AAVSO): RTN http://www.aavso.org/
On Oct 4, 2009, at 3:26 PM, Steve Welch wrote:
Terry, I know you are more concerned with trying to record this event, like me, but I am sure in the Palm Beach County Astronomy club, there are a lot of hard-core photons on eyeballs types. I know they dominate my Albuquerque club, so I wrote up my take on the eyeball observing prospects of the LCROSS impact next Friday. Thought you might be interested or maybe want to pass it on.
I didn't address the additional problem you'll have on the East Coast of trying to observe this with the sun up. Of course, that will make the event much harder to observe with eyeballs. It will also shift the aperture needs way up, since in order to see the event, you'll need to throw away a large part of the light with an orange or red filter and a polarizer. Also, you'll want to get and stay dark adapted, which will be very tricky with the sun up. A black cloth hood or darkroom changing bag with your head and the telescope eyepiece inside it will probably be necessary unless the event is close to the brightness of the lunar surface.
Hmmm... this could make for some good video on America's Funniest Home Injuries, when the black-hooded observer, duct taped to the telescope, falls off the ladder! ;-)
...Just kidding!
St
---
Steve Welch -- swelch@complex.org or swelch@philzimmermann.com
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Begin forwarded message:
From: Steve Welch <swelch@complex.org>
Date: October 4, 2009 1:00:10 PM MDT
Subject: Re: [TAAS-L] telescope needs for lcross
Reply-To: TAAS-L <TAAS-L@unm.edu>
With all due respect to the NASA web site, IMNSHO, NASA's implication and occasional pronouncements that "only big telescopes will have a good chance of observing this event" is highly misleading. Actually, the web site is not totally consistent on this assertion; on the front page of the observation site it now says, "...Mission scientists estimate that the Centaur impact plume may be visible through amateur-class telescopes with apertures as small as 10 to 12 inches..." , but down deeper, it has more detail, including the great uncertainty of the predictions of the brightness of the plume. According to the guesses by various people with opinions (some of them "experts", or as the National Enquirer would put it, TOP NASA SCIENTISTS SAY! --exclamation point required ;-), the brightness of the plume will be between 6th and 11th magnitude. That's a factor of 100 in uncertainty in brightness! I have, in my usual sloppy half-assed fashion, scanned all the reasoning and hastily examined the math behind the guesses, and I believe that it will be near or beyond the bright end of the brightness estimates. Note that many years ago, I was identified by the National Enquirer as a TOP NASA SCIENTIST! (ask me about it sometime when you have nothing to do for an hour or two--I love to talk about myself! ;-), so I have some authority here.
Seriously, though, no matter what the brightness of the ejecta plume is within the predicted range, it would NOT take much aperture to see it through a telescope, if this plume occurred in a dark sky. Even an 11th Mag planetary nebula as small as this object is going to be (a few arcsecs across) would be a cinch to see in a decent 3 or 4 inch scope. The problem is that with the gibbous moon surrounding the event, the contrast between the plume and the crater shadow against which we will be seeing the plume will depend mostly upon the amount of scattered light from the moon. So, we want clear skies and clean optics, most importantly! A 16" SCT with a dirty corrector plate, mediocre baffling, and/or some poor or damaged blacking on the secondary mirror mount is going to be less likely to see it than a perfectly clean 100mm refractor with a decent multicoated high power eyepiece. Again, this is In My Not So Humble Opinion.
I and other people have done some tests and I feel confident that we will be able to record this event on video, even if it is on the dim side of the predictions. At GNTO, I feel confident that we will be able to see and record the plume with both the 16" Isengard Newtonian and the 6" Astrophysics refractor at video or near video frame rates, working with focal lengths around 5 meters.
Things are not so certain with respect to observing the ejecta plume with actual photons on eyeballs, though... As we all know, contrast is a factor in being able to see faint objects with our eyes looking through eyepieces. However it is not the only factor. In addition, the human eye has a dark adaptation "problem" that we are all familiar with. If this event is on the dimmer side of the predictions, this will be the most important factor. That is, on the bright side of the predictions, the "surface brightness" of the event will be as bright or brighter than that of the sunlit moon, and just about any scope with a high enough power to resolve the shadowed part of the crater we will be looking at (Cabeus) will be able to see the crater shadow (about 20 x 5 arcsec) partly "fill in" behind the mountain peak that is in front of the shadow. On the dim side of the predictions, *assuming the scattered light present in that "black" crater shadow is low enough*, seeing the plume with your eye will be a function of how dark adapted your eye is.
There are two components to dark adaptation (at least--I'm not an expert on this). One is the eye's iris diameter, which shouldn't be a problem here, since we will all be observing this event with as high power as possible (tiny exit pupils for the light cylinder coming out of the eyepieces). The second is the chemical (and electrical?) sensitivity of the eye's receptors to light. (Actually, I am ignoring the fact that there are two different kinds of receptors, rods and cones--hopefully, you'll let that pass for this discussion, although it may be a complicating factor here--as I said, I'm no expert). The bottom line is that there is an automatic gain control process that takes place in the eye/brain system, enabling us to clearly see in light conditions that vary from a bright sunny day to a moonlit evening. There is about a factor of one million difference of illumination between these two conditions (look it up!) The human eye's Iris can only vary over a factor of about 200 or so (~0.5mm to ~7 mm diameter) in light gathering power. To observe this event with your eyes (again, if it is on the dimmer side of the predictions), you'll need to be as dark adapted as you can be when observing the moon through a scope. This means the sunlit portions of the moon must be as dim as possible, which in turn means you want to use as high a power as possible. Also, you'll need to preserve your dark adaptation by not looking at the moon with your naked eye before the event.
The best finder chart I've found for this is a processed image taken here in by someone here in New Mexico with a 24" scope. A link to the image is here:
http://astronomy.nmsu.edu/rthamilt/LCROSS/media/NMSU_LCROSS_new_target.png
Note that the image this finder chart is based on was taken last month, so the night of the event it will look somewhat different--I think the shadowed area the plume will appear against will be a bit smaller, but I am not sure. More importantly, the field of view here corresponds to an eyepiece field at about 1300 power, so you will be seeing more of the moon than this through your eyepiece (very likely!).
Good Luck, all!
St
On Oct 4, 2009, at 10:39 AM, William Ferrell wrote:
Dee
Finally got around to reading those emails sent earlier concerning lcross event. Apparently, only the big telescopes will have a good chance of viewing the event.
I plan to be at your place on 9 Oct for event.
According to NASA web site, the scope will need minimum of 200x magnification, but higher is better. My scope has the aperture but it would be good if someone would bring an 1.25" eyepiece of 3 or 4mm to use as I have no eyepiece that small. Also I imagine that the brightness could be a problem and suspect a moon filter is equally necessary. I have no such filter.
Guess we will do with what we've got but, if someone is coming to Dee's star party (is that what it is??) and has such items, it would be appreciated.
Will
