Observations by Curtis Roelle S1C
Subject: Observations of Impact Sites From Westminster
Instrument: Tectron 20
Optics:
Newtonian Reflector
20-inch aperture
F/5 focal length
Mounting:
Open truss
Dobsonian (altazimuth)
Magnification:
195x (13 mm Televue Nagler)
362x (7 mm Televue Nagler)
Abbreviatons
GRS Great Red Spot
Sf South-following
Sp South-preceeding
Thursday, July 28
Observed from 8:45 - 10:30p EDT starting with impact complex labeled
K/U/W on finder charts generated using Jason Goodman's
"jup_realtime_letters.pro" IDL program.
These observations were made using a yellow #15 filter from Orion.
Before twilight ended two dark regions were visible, but their
separation was greater than indicated by the charts. The leading spot
transited approx 1:05 UT (+/- 5 minutes); nothing appeared on the
chart at this position. The spot was fairly dark, but not as dark as
the second spot following it as Jupiter rotated.
The second spot was the darker of the two. It had an elongated delta
shape, with a linear protrusion extending from its "nose" in the
direction of rotation, pointing toward the leading spot, protruding
approx. 1/2 the distance to it. According to Jason Goodman, this spot
contains all of the spots labeled K, U, and W on his finder charts.
Between both spots and to the south, and slightly closer in longitude
to the leading spot, was a third, tiny brown spot. It appeared to be
connected to the leading spot by a faint brown bridge, lighter than
the spots themselves, but darker than Jupiter's bands. During moments
of good seeing, there were hints of a much fainter bridge connecting
the third spot to the second spot. The charts had nothing marked at
the position of the third spot.
Here is an ascii sketch of what this region looked like:
.
/ `
O --O (South Up)
1 3 2 <--- Direction of Rotation
The spots are numbered in the order in which they are discussed above.
The South Tropical Band had an interesting feature. It was darker
where it passed north of the impact regions discussed above.
By the time the L and G spots had rolled around to the front the
seeing had degraded considerably and some clouds in the southwest
started to interfere.
Tuesday, July 26
Observation began at 8:50p EDT after clouds cleared with fair seeing.
Used updated finder charts which represent each spot with a letter
whose font is proportional to the size of the impact region. As the
finder charts evolve, the identification of regions already observed
keep changing and is a significant problem.
Spots U and K (?) were already past transit. Both are small, very dark,
and appeared similar in size.
L was large and circular and about one hour prior to transit. A darkening
along the morning limb was G, experiencing local sunrise. Even at
this glancing view, the complexity of the G region was readily apparent.
As G became better placed for observing at 10p EDT, the dark needle-like
extension viewed Sunday (July 24) could be seen protruding from G along
the direction of rotation.
At 10:30p EDT, as G was approaching the Meridan, it could be clearly
discerned as a double spot. The spot that immediately trailed G, as
Jupiter rotated, and slightly to its north, was the S region (or
possbily R?).
At 11p EDT some clouds started to interfere by dimming the image that
was already shimmering quite badly.
Sunday, July 24
Observation began several minutes before 9p EDT, prior to end of civil
twilight. L and G regions both appeared to be rather complex. L has
a dark center, and a linear feature tangent to its SW edge that extended
NW-SE. Let "." represent the dark center and "/" the linear feature;
L looked like this: "/." (south up).
Circular and linear features were visible at region G, which appeared
to be either a system of three or more impacts, or perhaps a result of
that region's evolution and development. There was a small black
circular spot which had at its southern edge a linear protrusion
stretching out to the west (direction of rotation). In addition
another dark area flared south and east, away from the circular spot.
The use of a Yellow #15 filter improved the contrast of the impact regions.
As rotation carried these two regions toward the evening terminator,
two other spots came into view from the morning side. These were
evidently Q1 and H (but I could be wrong). The Q1 candidate was very
small, circular and dark. H was a little larger, and somewhat
elongated N-S.
Another very small spot formed a triangle with Q1 and H, located
between but at a higher southerly latitude. This spot does not
correlate with any impact sites on the finder charts that I had
available.
It was good weather and a favorable configuration of impact sites. At
around 10p EDT all five regions described above were visible at the
same time.
Saturday, July 23
Although skies were hazy with occasional clouds passing in front of
the planet, Jupiter sported two small black wounds from Shoemaker-Levy
9. These regions were either from fragments A and C or from C and
K/U/W.
Experimentation with a set of visual filters from "Orion Telescope
Center" was performed. The red #25 showed no improvement at all, and
the Blue #80A had minimal improvement, although the latter did help
with Jupiter's brownish cloud bands. The green improved contrast, but
the yellow #15 was the best. With the yellow filter the spots
revealed more structure and added a warm inviting tint to the planet.
As Jupiter was sinking toward the southwestern horizon and the seeing
suffered more from the thicker atmosphere through which Jupiter was
being viewed, a large dark region appeared at the morning limb: The L
fragment's impact region was rotating into view. by 11:30 p.m. the
seeing because of Jupiter's low altitude had deteriorated to the point
where the bands were no longer visible.
I have noticed that some impact regions (at least K and L) appear
large when viewed along the limb, but as they move away from the limb
they tend to "dissolve", leaving behind a small dark impact site.
WEDNESDAY, JULY 20 (fragments H, E or F, and K)
Skies clear and free of haze. Started observing at 9p EDT near end of
civil twilight. The GRS had already transited and two dark impact
regions were visible. With respect to the GRS and direction of
rotation one impact site was Sp and one was Sf. The former was
nearing the limb and I suppose this was the impact from SL-9 fragment
H, a fairly old impact which was on its 7th revolution of Jupiter.
Initially I thought the second region was the impact from fragment F,
but its location corresponds more closely with that predicted for the
older impact site of fragment E.
During moments of good seeing at 362x region E (or F?) seemed to be
located along the following edge of a gray oval ring. The ring was
not complete and resembled a letter "C" with the open part facing the
direction of rotation. The area inside the oval ring was as bright
as the area outside. Perhaps this ring is what remains of the
healed over impact region from fragment F?
At 11:45p EDT the impact region from fragment K had rotated into view. By
this time the seeing had degraded due to Jupiter's decreasing altitude as
the entire planet shimmered and boiled.
TUESDAY, JULY 19 (fragments G, L, and H)
The sky was very hazy and the Moon was heavily obscured. However,
Jupiter was visible to the naked eye. I began observing the planet
from my driveway at 10p EDT.
At 195x Jupiter appeared to have two huge dark eyes staring back from
its southern hemisphere. One spot was near the central meridian,
while the second was preceeding it about 2/3 of the way to the limb.
Both spots appeared to be comparable to the diameter of Earth, with
the central spot being the larger of the two. At 365x the central
spot looked a little darker toward its center.
These impacts were from the L (near the limb) and G (central)
fragments. The impact site from fragment L was only four hours old
when I started viewing it.
These spots were so prominent they would certainly have been visible
in smaller instruments -- probably even in a 3" refractor or 4"
reflector. A friend of mine in California reported easily observing
impacts from two smaller fragments with an 8" reflector on Sunday
night from California.
The L impact region rotated around to the backside within about 1/2
hour. Then as the G region was approaching the limb at 11:15p EDT I
noticed a third impact site had rotated around to the front. It
looked like a little black dot, much smaller than the G and L regions,
but still more prominent than the shadow of a Galilean satellite (not
to mention at a very high southerly latitude). This impact was almost
certainly caused from fragment H, whose predicted Jovian impact time
was Monday at 3:26p EDT.
Curt Roelle Curtis_Roelle@jhuapl.edu
Space Department / Space Sciences Branch
Johns Hopkins University -- Applied Physics Laboratory