I Saw the Impact Site

Date: 2009-07-24
Time: 02:11 UT
Location: Snellville, GA
Telescope: 10-in f/4.5 Dobsonian, stopped down off-axis to 3.5-in f/15
Magnification: 110x
Object: Jupiter and impact site
Seeing: 4 (0--4)
Atmosphere: Moderate clouds passing over Jupiter.

Again, I'm adding this entry after the fact. Here are my live tweets. (Tweet times are EDT).

Jupiter I can see the impact site. It is tiny and intense black. It comes and goes in the seeing.10:11 PM Jul 23rd

jupiter I am literally observing through passing clouds. The planet is fading in and out.10:13 PM Jul 23rd

Pickering Seeing Scale

I used to always keep the Pickering seeing scale with my notes. Here it is from Sky and Telescope for reference.

…here is the scale in its early form as described by Harvard College Observatory's William H. Pickering (1858-1938). Pickering used a 5-inch refractor. His comments about diffraction disks and rings will have to be modified for larger or smaller instruments, but they're a starting point:

1 — Star image is usually about twice the diameter of the third diffraction ring if the ring could be seen; star image 13 arcseconds (13") in diameter.

2 — Image occasionally twice the diameter of the third ring (13").

3 — Image about the same diameter as the third ring (6.7"), and brighter at the center.

4 — The central Airy diffraction disk often visible; arcs of diffraction rings sometimes seen on brighter stars.

5 — Airy disk always visible; arcs frequently seen on brighter stars.

6 — Airy disk always visible; short arcs constantly seen.

7 — Disk sometimes sharply defined; diffraction rings seen as long arcs or complete circles.

8 — Disk always sharply defined; rings seen as long arcs or complete circles, but always in motion.

9 — The inner diffraction ring is stationary. Outer rings momentarily stationary.

10 — The complete diffraction pattern is stationary.

On this scale 1 to 3 is considered very bad, 4 to 5 poor, 6 to 7 good, and 8 to 10 excellent.

Jupiter and the Asteroid Impact Site

Date: 2009-07-22
Time: 04:33 UT
Location: Snellville, GA
Telescope: 10-in Dobsonian f/4.5
Magnifications: 44x, 110x
Object: Jupiter
Seeing (scale 0--4) Started out at 1 and worked it's way up to 3.
Atmosphere: Light clouds. Cool air for the summer.

I'm entering these notes nearly two days after the observations.

I started observing before the telescope had come to temperature. Also Jupiter was quite low in the East so, from at least those two factors, the seeing was quite terrible. The four Galilean moons were dancing sparklers and it was very difficult to see any detail on the planet other than the main belts.

I'll include the tweets I made at the time.

Observing Jupiter. 10-in f/5.4 Dob, 110x. Seeing is terrible, 1 (0--4). SEB and GEB easy but no GRS or impact site.12:33 AM Jul 22nd .

As the planet rose higher and the telescope settled down, the viewing was much better. I was easily able to see the North Equatorial Belt and the North Temperate Belt (NTeB). The South Equatorial Belt (SEB) was also easily divided into it's two parts.

Seeing is better, 3. Tel has settled down and planet is higher. NEB a d belt just north easy. Still no GRS or impact.12:47 AM Jul 22nd

I couldn't see the GRS, Great Red Spot (hollow), at all though it may have rotated to the limb at the time.

As the seeing improved, the four moons became tiny disks. One was leading (Io) and three following (Ganymede, Europa and Callisto from west to east away from Jupiter). The identification is based on Sky and Telescope's moon Javascript program.

For much of the time I used the 3.5-in aperture stop which makes my Newtonian an f/15 unobstructed off-axis telescope. Most observing was done at 110x.

By 5:00 UT thin clouds covered the planet but I continued to observe through them. They mainly just attenuated the brightness.

I was never able to resolve the impact site. It should have been there but at this magnitude, with the seeing and maybe my eyes, I couldn't resolve it. I could see a lot of belt detail and could see the belts including the dark higher latitude belts in the South.

I can see excellent belt detail but no impact site visible in North. Maybe it's smeared?1:01 AM Jul 22nd

Well I don't see it. The SEB appears split in two. I can see the faint belt N of the NEB. But no impact site.1:19 AM Jul 22nd

I stopped observing sometime around 5:19 UT.

Reference: Sky and Telescope Jupiter Observing Guide

Trying a web log

I kept an observing notebook for many years. Recently I pulled my 10-in f/4.5 Dobsonian telescope out of it's storage cabinet, dusted it off, fixed the ailing mirror cell, cleaned all of the optics except for the primary, collimated it and took it out for a spin.

It occurred to me to try logging observations with Twitter and maybe a blog. So here it is. This may not work too well. For one thing, I don't know if I can dim my phone display enough for it to be useful for entering notes when observing in the dark. However, in my driveway where I have a nearby street light and other lights, and I was looking at Jupiter, it worked okay.

As is often the case, this is an experiment.