Monthly Archives: November 2010

Nov 27: Several clear hours, sudden cloud.

Saturday evening. There is snow cover on the ground now, and we had freezing rain yesterday, so it certainly feels like winter is in the process of arriving. There were snow flurries this morning, but the sky cleared up mid-afternoon and is still clear now. The temperature is -6 in the dome.

2010-11-27-M15-SC-01-DDPAbout 6:00 I went outside and opened up. I hope to do some data gathering on galaxy NGC2403 tonight, but it is presently behind my large pine tree, and won’t be in the part of the sky I can see until about 9:00. M15 is presently well situated, though, so I am taking a couple of hours of exposure on it, in a mix of 1- and 5- minute subs (thinking I may want the 1-minute subs to mix in to bring out detail in the core, which will otherwise likely be overexposed).

2010-11-27-NGC2403-SC-02-DDPAfter an hour and a half of data gathering on M15, NGC2403 has risen above the hedge, so I’ve switched over to that, about 8:15 PM. I’m gathering 5- and 10-minute subs.

After 1.5 hours, my session was cut short. The sky clouded over completely, very suddenly. Within one 5-minute exposure it went from clear to flat gray. So, I closed everything down and called it a night.

Adjusting G11 Worm Gear Backlash

The Losmandy G11 mount in the observatory is fitted with the OVision upgraded worm gear for higher-precision tracking. This page illustrates the adjustment of the slack for this gear – the amount of “looseness” between the worm and the gear mounted on the RA shaft. An equivalent adjustment is available on all mounts, and the right balance of looseness (for smooth tracking) and tightness (for minimal backlash) must be found. OVision gears are run quite loose. Continue reading

Nov 10: More M27, start 2 new targets

Tonight looks like a repeat of last night – the sky is clear and the CSC says excellent transparency all night. I’ve opened the dome at 7:30 PM, and am taking another 2 hours of M27 in 15-minute subs, to add to the data collected the last couple of nights.

I just noticed that for the first 500 seconds of the first 900-second sub, I forgot to turn PEC on. It was still guided, but more correction needed than I would have liked. So I may end up discarding this first sub – we’ll see how it turns out. The other 1.75 hours will be PEC-corrected in any case.
Sure enough, in post-processing Maxim recommended discarding the first sub (and another) for poor star-roundness, so I went along with this. The result, with 4.5 hours of data, is starting to look nice – detail in the outer gas envelope is beginning to show well.

Continue reading

Clear night: More M27 time and some other targets

November 9, 2010. The moon has set and, with DST over but no snow cover yet, it is surprisingly dark in my back yard. It’s clear and not too cold – about 5 degrees.

2010-11-08-M27_0Gathered 2 more hours of data on M27, this time in 15-minute subs. I’ve bumped this up from 10-minute subs just to see the effect. I would expect slightly deeper results, and slightly better S/N, than with more shorter subs. On the other hand, the longer the exposures, the greater the chance that something like a passing plane will ruin them. So I’ll try 15 and see how that works, and maybe push even longer for the next run.

Watching the guiding graph, I note that RA guiding is still tending to oscillate back-and-forth across the zero axis, so I have tried turning the x-aggressiveness down a bit, to 60%, to see if it can further smooth out the curve. Watching the results for a couple of minutes, it does seem to have resulted in a flatter error curve. Continue reading

Improved Periodic Error and some M27 Data

The CSC predicted clear skies last night, but reality disagreed, and it was completely overcast. Tonight seems better – the sky is clear and steady, and it’s dark earlier because today is the day we went off Daylight Savings time. It’s cold out – 1 degree Celsius.

Yesterday during the day I adjusted the RA worm gear, increasing the slack to the OVision specs, hoping that will improve the Periodic Error of the mount, so tonight I am doing a PEMPRO run to get new PE data and generate a new PE Correction curve. I’ve just started a 15-minute data gathering run, and am typing this from inside while the data collect.

The initial run gave under +/- 4” error, with a reasonably repeating curve (which already seems better than the rather ragged guiding track I was seeing the other night, before adjusting the RA slack). Better, the frequency plot of the error showed it is largely periodic on the worm cycle, so it will respond well to PEC. So I uploaded a calculated PEC set to the mount, and did another data gathering run with PEC turned on.

Oops. The new run had a weird spike in data right at the start, and I realized that I had slewed the scope but then not taken the slack out of the RA gear. So it took until the RA drive “crossed the gap” of the RA backlash before accurate tracking was underway. Lesson learned, and I started the run again.

Great results – PE with correction is now showing at +/- 1.1”. Continue reading

Back up after a long break

The usual Autumn stretch of poor weather, combined with the municipal election, kept me off the air for several weeks. Tonight conditions were very good, but cold, and I started everything up again.

More configuration work was needed, still recovering from a computer hard disk change a few months ago. Then I recalibrated the mount’s home position (using a great method from Arizona Skys), re-did a sky model, and did some tests. Periodic error is a little more ragged than I would like, so some daytime session I’ll check and adjust the play in the RA gear.

Meanwhile, most of the raggedness could be guided out. I took a few test images for fun. This one, of M27, shows nice colour. It’s a simple stack of 3 10-minute exposures, uncalibrated. (I need to collect a new set of Flats and Darks, which I’ll do with the dome closed next free and cloudy night.)

Still to do: I have no reference data for setting the colour balance when de-bayering images from this one-shot colour camera. I plan to gather either some bright moon surface images or some G2V stars (ideally, both) to calculate proper colour ratios.