Last entry: Sept. 1, 2008
   

 

Pluto: Visual Sightings Logbook
Introduction
This log is a log of small-scope, visual sightings of Pluto, that I've compiled from the Internet.  It will assist Pluto spotters by providing a record of the telescope type, aperture, power, and viewing conditions employed by successful observers.

Since the 203-mm/8-inch instrument is pretty standard fair and has the light-grasp to easily see the planet, I consider "small-scope," for Pluto viewing purposes, to mean instruments with objective diameters of less than  152-mm/6-inches -- mostly those much less.  

At first glance, many of these entries seem impossible; instruments this small seem to defy limiting magnitude norms for visual detection of the planet.  For these entries is Pluto in the "eye of the beholder?" -- the brain "filling in the blank" with expected data?  

But, consider that magnitude limit formulas (such as:  4.5 + 4.4 * Log D, where 'D' is aperture in millimeters) are empirically derived from observation.  As solely a function of aperture, the formula doesn't account for the variability in quality of the observer, optics, or sky: these are averaged and accounted for in the fixed terms.  Formulated aperture limits should be exceed by someone with any combination of exceptional eyesight, optics, and observing location.

Entries are sorted by decreasing aperture of the telescope, in mm/inch format.  If you know of any similar observation reports posted on the Internet (on a web-page, message board, newsgroup posting, etc.), that don't require passwords to access, send me the link for evaluation.

Log Entries

140-mm / 5.5- inch

 I'm happy to say that after quite a struggle I did manage to see it in my 5.5" refractor under reasonable but not pristine skys (about mag 5 outer suburban).
--T.W.     more

114-mm/
4.5-inch

 'I have observed pluto many times through my 4.5" f/7.9 reflector,...'
-- J.M.     more

102-mm /
4.0-inch

 'With difficulty and always using averted vision at 176x and 220x, I could see a very dim "star" at the location where Pluto should be. There should be no star there and there are no other stars in the vicinity.'
-- R.B.     more

94-mm/
3.7-inch

 'One evening last year, I found Pluto in my ten inch and then used my variable aperture stop to stop things down to around 94mm. I could still just "barely" see Pluto even at that aperture.'
-- D.K.     more

92-mm/
3.6-inch

 "I need some help to back up an observation I made of Pluto at approximately 12:30-1 AM PST on 5/28/00 at RTMC (7600') with a 92mm refractor. Seeing was good in this aperture and the magnifications used (112x, 150x)." 
-- D.W.     more

90-mm/
3.5-inch

 'When I found it easily in my 8", and knew it was in a star-poor area, I tried my 90mm Mak. It winked in and out, but was in the same star field. It was hard, but not impossible.' 
-- D.P.     more #1     more #2

81-mm/
3.2-inch

 '... also with a 3.2" refractor several times last apparition. In my experience Pluto is an easy target with small apertures under decent skies (although 3.2" is pushing the envelope a bit for me).' 
-- J.M.     more

70-mm/
2.8-inch

 "Anyway, I got several reliable detections at 95x in the Pronto..." 
-- B.S.     more #1     more#2

 

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