Jun 192017

The sky last night was one of the darkest (and clearest) we have had in quite a few weeks. I was able to get a short JunoCam series before Jupiter hit my western tree line.

Ideally, if you want to image for an hour, the best time as far as the atmosphere is concerned, is the half-hour before the target gets to the zenith and the half-hour after it passes the zenith. But right now Jupiter gets only 55° high and is well past the meridian before the sky gets dark. That means the planet starts with less than optimal airmass and as the night progresses descends into ever increasing airmass.

Airmass is the length of the pathway through the atmosphere that the photons from the object you are looking at have to pass. The path length above the zenith is about 100 km and the path length along the horizon is about 1020 km. By definition, airmass is 1.0 for an object directly on the observer’s zenith. The lower in the sky, the higher the airmass gets. The longer atmospheric path means more distortion, absorption and refraction.

Close to the horizon, the object doesn’t look like it really does (distortion), isn’t as bright as it really is (absorption) and isn’t where it looks like it is (refraction).

 Posted by at 20:11
Apr 232017

Last night the SkySentinel meteor camera that I host here at the PTO caught sight of a set of sprites as a weather front approached from the northwest. Sprites are only one of several “Transient Luminous Events” associated with thunderstorms. Reports by pilots of ‘lightning’ above the clouds were once dismissed outright by meteorologists. Once directly imaged in 1989 and finally accepted by scientists as a real phenomenon, sprites and their relations have been recorded all over the planet as well as from the International Space Station. One estimate has several million of these high-altitude events occur each year.

North is at the top; northwest upper right.

These electrical discharges occur 50-90 kilometers above the ground. The sprites in this video are only visible on two frames. Look carefully and you will see the flash of ‘normal’ lightning reflecting off of low lying clouds immediately after the sprites.

 Posted by at 18:50
Mar 112016

First, the PTO is finally back online. Now the painful details:

The original diagnosis of the new mount having a personality problem was incorrect. The control box and hand paddle checked out fine and were returned unharmed. As expected, the mount still suffered from pointing problems; both in positioning and parking. After an additional session of phone diagnostics with George from Astro-Physics (thanks George) the RA gearbox was dismounted and sent back to the factory for inspection and repair. George also requested the GTOCP3 control box accompany the gearbox (its second trip back home). The return paperwork listed new spur and cluster gears as the fix. While they had the control panel the troops at AP ran modeling software on the repaired gearbox and loaded a new PEC model into it.

With the repaired and reprogrammed parts reinstalled, the mount was ready for testing. We finally got some clear skies to align and test it and the results are amazing. With the old mount I was able to reliably take an unguided 30 second exposure without any visible distortion in a star’s image. A guided 300 second image would routinely pass a 0.2 roundness test. Now I can take an unguided 300 second image where the stars routinely pass a 0.05 roundness test.

The old mount’s less than optimal performance is not entirely its fault. First, I had loaded the mount right to its advertised limit (and over time probably a little more). Also, the polar alignment was off slightly in elevation. I found making fine adjustments to the elevation axis very difficult. I’m pretty sure this was mostly due to the design of the adjusting mechanism dealing with the weight the mount was carrying.

Of course, the primary reason for the observatory upgrade was to increase the load capability of the mount for the new (refurbished) telescope.

Installing the new scope will be the final step in this PTO upgrade. Watch this space.

<<< Progress report (Part 2) Progress report (Part 4) >>>
 Posted by at 11:22
Jan 272016

I am still fighting the somewhat troublesome new mount. When the mount is commanded to slew to a target it gets close but does not center it, even in a wide FOV eyepiece. Most importantly, the mount does not track precisely. Even in a short 30 second exposure the stars streak significantly. Finally, the mount also does not park all the way. It also gets close but does not reach the designed position.

After several fruitless iterations of user group questions and answers, the group moderator had me call the factory and talk with the technicians. A short troubleshooting session over the phone led the technician to a quick diagnosis. His suspicion is the control panel thinks it is on a different model mount. He classified it as a ‘personality’ problem. It is technically possible to update the control panel’s internal settings over the internet, but the “regular crew chief” is out sick, so the control panel is now in the hands of the post office.

Meanwhile, I have had plenty of time (and adequate weather) to resume work on the floor panel reconfiguration. Now finished, it is obvious which panels are new due to the new carpet, but they should weather fairly quickly and blend in once summer arrives and drives the temperature up in the dome room. But, most importantly, I can now pull up the floor and work on the wiring and plumbing without having to disconnect anything.

<<< Progress report (Part 1) Progress report (Part 3) >>>
 Posted by at 11:13
Jan 112016

The floor tasks have been put on hold for more conducive weather conditions and to be ready for the occultation on the 12th.

The original configuration of the control wiring and plumbing through the floor has been restored. However, the wiring configuration at the mount has changed drastically. The AP1600 allows the cabling to the focusers and cameras to be routed through the mount. I’ve rolled the dice and also routed the cooling hoses through it as well. This routing scheme significantly reduces the chance of wiring or hoses snagging on something. The size of the Losmandy mount prevented through the mount cabling so it was all external.

One of the challenges of a German equatorial mount has always been cable routing. Over time I had come up with a fairly good configuration, but there were certain positions in the sky that could result in a temporary snag. These weren’t critical enough to damage equipment; they would just cause enough drag to upset the guiding and ruin an exposure. The snag would then release and most of the time the mount guiding would recover. Once in a while I would have to go into the dome room and adjust the way the cables were hanging. Hopefully, that tasking is over.

So, here is progress made in the list of upgrade tasks:

  • The scope has been balanced. The mount is fairly stiff and with the current weight load nowhere near the advertised limit, balancing it was not as finicky as the Losmandy. I still have another counterweight in the box for the 12.5″ scope. It may not be enough.
  • The new ASCOM driver has been installed and is operational. Since the polar alignment software that came with the mount required it, installing it was moved up in the list. So far, all the supporting software packages seem to be playing well with the new scope control system.
  • I started the polar alignment process on the 6th of Jan. and was able to get most of the way through it before clouds moved in. Finished initial alignment on the 7th.
  • Characterizing any periodic error has not been accomplished yet. All recommendations that I have found said to perform the mount alignment first.
  • In order to accurately position the slit in the dome, the dome controller needs to know where the mount RA axis of rotation and Dec axis of rotation intersect. If that intersection is not at the center of the dome, the differences need to measured and entered into the mount driver. Obviously the new mount is at least 18″ higher in the dome with the pier spacer. The intersection of the mount RA and Dec axes are also not the same as the G-11. So, I had to restring the dome and measure the new offsets. That has been done.

The AP1600 has 4 predefined parking orientations. I always parked the G-11 in the traditional equatorial position that everyone thinks of; telescope pointed at the north celestial pole with the counterweight bar down. However, that position is not the preferred position for this mount. Park position #4 has the telescope parallel to the ground facing south and the counterweight bar parallel to the ground facing west. It is definitely unconventional looking but has a totally unanticipated benefit. With both axes parallel to the ground and with the addition of the 18″ pier spacer, the lowest point of any piece of equipment is 6’2″ above the floor. I can now walk around the dome room without fear of bumping the mount and having to re-do a mount alignment.

UPDATE: There is significant star streaking during a 30 sec exposure. I have spent the last two days trying different techniques to eliminate the streaking. So far, no joy.

<<< PTO Upgrade Progress report (Part 2) >>>
 Posted by at 14:44