| Notes
from the Imagers: |
Clyde Tombaugh discovered Pluto in early
1930 after taking two exposures of the same section of the sky 6 days
apart. It was not by accident that he found the 9th planet for his job was
to systematically image the area of the sky around the ecliptic in the
hopes of finding the long sought and elusive 'Planet
X.' When he was not photographing, he was comparing pairs of plates to
find a 'star' that moved between them. Clyde took 60 minutes exposures
using a 13-inch (3 lens element), f/5.3 refractor called an astrograph (an
astrograph is a telescope that has a wide field of view). The Lowell
Observatory does not have any information about the film speed of the
original 14x17 inch glass plates used, but after seeing copies of the
original discovery plates, I estimate that the film speed was no higher
than 50, probably 25 or lower.
In Clydešs honor, I imaged Pluto on
emulsion, using off-the-shelf ISO400 negative film, with a 4-inch Tele
Vue, TV NP101 refractor working at f/10.8 (used a barlow). My
Astro-Physics 155 F7 Starfire EDF served as the guidescope with an
attached ST-4 autoguider. The biggest advantage I had over Clyde is
knowing exactly where Pluto is located and I obtained this information
from the Astronomical Calendar 2003 by Guy Ottewell. Pluto was
around magnitude 13.8 at the time I took these pictures. The 13-inch
astrograph had 10 times more light gathering capability than my 4-inch
refractor but todayšs modern films far surpass those of 1930 so I was
able to easily image our smallest planet in just 20 minutes.
-- ken graun |
