Sky transparency — night of 19–20 September 2026

Cloud arrived at 19:15 — detected by the all-sky camera, independent of N.I.N.A. Before it the sky ran at index 0 (IQR 0–0); after it 69 (IQR 39–85). 0 of 81 light frames landed before the cloud. 51 of 51 failures are attributed to cloud. Guiding held at 0.98″ RMS (RA 0.62″, Dec 0.76″) over 8.1 h; the worst minute was 7.18″ at 04:30. The 03:39 autofocus run fitted its curve on almost no stars and should not be trusted. The 04:57 autofocus run fitted its curve on almost no stars and should not be trusted. Morning sky flats: 60 frames (H 20, O 20, S 20), 06:06–06:10, auto-exposure 1.5–3.2 s.

Index before 19:15

0 · IQR 0–0

Index after 19:15

69 · IQR 39–85

Cloud onset (all-sky)

19:15 · independent

Errors after onset

51 of 51 · solve + PHD2

Guide RMS

0.98″ · RA 0.62 · Dec 0.76

Normalised transparency index, by filter

100 = that target and filter's own clear‑sky median (rolling median over recent clear nights). Shaded columns are autofocus runs; the first target is named at the top left and dashed vertical rules mark each target change; ticks along the base are errors.

H α O III S II ▲ Plate solve failed ◆ PHD2 error

All‑sky background brightness

Mean luminance of the upper sky per all‑sky still — independent of anything N.I.N.A. recorded. The camera auto‑exposes, so this is an instrumental number, not photometry.

PHD2 guiding

RMS tracking error per minute from the PHD2 guide log, taken about zero rather than about each minute's mean, so slow drift counts as error. 2036 guide frames over 8.1 h of guiding in 23 sessions; the gaps are slews, dither settles and autofocus runs, when PHD2 was not guiding. PHD2 discarded 553 further frames — usually a lost star. The worst minute (7.18″ at 04:30) is clamped at the top of the plot.

RA RMS Dec RMS ◆ PHD2 error

All‑sky frames at the key moments

Times come from the still filenames, so they line up with the charts exactly.

All-sky at 19:12 — **19:12** · start of night

All-sky at 19:15 — **19:15** · cloud onset

All-sky at 20:12 — **20:12** · peak brightness 170.0

All-sky at 05:47 — **05:47** · end of night

Clear‑sky reference medians

The divisors behind the index — median detected stars per light sub before 19:15.

Target	Filter	Median stars	Frames	Source
NGC 346	H	731	28	earlier clear nights
NGC 346	O	680	27	earlier clear nights
NGC 346	S	843	25	earlier clear nights

Event timeline

All observatory events with their attributed causes.

19:48:08solve failedASTAP plate solve failedcloud

19:48:26solve failedASTAP plate solve failedcloud

19:48:43PHD2failed to find a suitable guide starcloud

19:49:04PHD2failed to find a suitable guide starcloud

19:50:18PHD2failed to find a suitable guide starcloud

19:59:26solve failedASTAP plate solve failedcloud

19:59:32solve failedASTAP plate solve failedcloud

19:59:43PHD2failed to find a suitable guide starcloud

20:00:57PHD2failed to find a suitable guide starcloud

20:06:22PHD2failed to find a suitable guide starcloud

20:15:24solve failedASTAP plate solve failedcloud

20:15:38solve failedASTAP plate solve failedcloud

20:20:29AF failedautofocus run started 20:15:34 did not completecloud

02:28:33PHD2timed-out waiting for guider to settlecloud

02:43:31PHD2Guiding stoppedcloud

02:46:21PHD2timed-out waiting for guider to settlecloud

03:06:14PHD2timed-out waiting for guider to settlecloud

03:08:20PHD2timed-out waiting for guider to settlecloud

03:13:24PHD2timed-out waiting for guider to settlecloud

03:21:24solve failedASTAP plate solve failedcloud

03:21:43solve failedASTAP plate solve failedcloud

03:23:32PHD2timed-out waiting for guider to settlecloud

03:28:36solve failedASTAP plate solve failedcloud

03:28:55solve failedASTAP plate solve failedcloud

03:34:33PHD2timed-out waiting for guider to settlecloud

03:47:51solve failedASTAP plate solve failedcloud

03:48:03solve failedASTAP plate solve failedcloud

03:50:09solve failedASTAP plate solve failedcloud

03:50:19solve failedASTAP plate solve failedcloud

03:52:26solve failedASTAP plate solve failedcloud

03:52:37solve failedASTAP plate solve failedcloud

04:10:13solve failedASTAP plate solve failedcloud

04:10:49solve failedASTAP plate solve failedcloud

04:16:24solve failedASTAP plate solve failedcloud

04:16:52solve failedASTAP plate solve failedcloud

04:20:44PHD2timed-out waiting for guider to settlecloud

04:25:49solve failedASTAP plate solve failedcloud

04:26:14solve failedASTAP plate solve failedcloud

04:27:57PHD2timed-out waiting for guider to settlecloud

04:33:01solve failedASTAP plate solve failedcloud

04:33:18solve failedASTAP plate solve failedcloud

04:34:19PHD2failed to find a suitable guide starcloud

04:45:01solve failedASTAP plate solve failedcloud

04:45:20solve failedASTAP plate solve failedcloud

04:47:06PHD2timed-out waiting for guider to settlecloud

04:52:27PHD2timed-out waiting for guider to settlecloud

04:57:32solve failedASTAP plate solve failedcloud

04:57:53solve failedASTAP plate solve failedcloud

05:10:46PHD2timed-out waiting for guider to settlecloud

06:04:20PHD2failed to find a suitable guide starcloud

06:04:41PHD2failed to find a suitable guide starcloud

06:05:12PHD2failed to find a suitable guide starcloud

All 237 frames (excludes the 60 sky flats — no stars to detect)

Time	Class	Target	Filter	Exp	Stars	HFR	Index
19:12:03	autofocus	NGC 346	L	5s	164	3.52	—
19:12:20	autofocus	NGC 346	L	5s	180	3.04	—
19:12:35	autofocus	NGC 346	L	5s	279	2.35	—
19:12:50	autofocus	NGC 346	L	5s	397	2.02	—
19:13:05	autofocus	NGC 346	L	5s	311	2.38	—
19:13:25	autofocus	NGC 346	L	5s	241	2.95	—
19:13:45	autofocus	NGC 346	L	5s	160	3.81	—
19:14:05	autofocus	NGC 346	L	5s	89	4.48	—
19:14:25	autofocus	NGC 346	L	5s	57	4.83	—
19:14:40	autofocus	NGC 346	L	5s	46	5.86	—
19:15:00	autofocus	NGC 346	L	5s	336	2.24	—
19:21:40	light	NGC 346	H	300s	392	4.16	54%
19:26:41	light	NGC 346	H	300s	355	4.40	49%
19:32:08	light	NGC 346	H	300s	388	4.23	53%
19:37:09	light	NGC 346	H	300s	371	4.32	51%
19:43:05	light	NGC 346	O	300s	282	4.52	41%
19:48:06	light	NGC 346	O	300s	2	4.68	0%
19:59:26	light	NGC 346	O	300s	0	0.00	0%
20:15:23	light	NGC 346	O	300s	12	5.00	2%
20:15:50	centering	NGC 346	L	5s	0	0.00	—
20:16:05	centering	NGC 346	L	5s	0	0.00	—
20:16:20	centering	NGC 346	L	5s	1	0.00	—
20:16:35	centering	NGC 346	L	5s	2	4.56	—
20:16:50	centering	NGC 346	L	5s	1	0.00	—
20:17:10	centering	NGC 346	L	5s	55	2.85	—
20:17:30	centering	NGC 346	L	5s	21	2.41	—
20:17:50	centering	NGC 346	L	5s	44	2.42	—
20:18:11	centering	NGC 346	L	5s	248	2.79	—
20:18:30	centering	NGC 346	L	5s	75	3.83	—
20:18:50	centering	NGC 346	L	5s	16	4.78	—
20:19:10	centering	NGC 346	L	5s	25	5.96	—
20:19:30	centering	NGC 346	L	5s	7	7.98	—
20:19:45	centering	NGC 346	L	5s	5	9.29	—
20:20:05	centering	NGC 346	L	5s	157	2.16	—
20:26:28	autofocus	NGC 346	S	300s	384	4.74	—
20:26:51	autofocus	NGC 346	L	5s	266	2.77	—
20:27:10	autofocus	NGC 346	L	5s	41	7.39	—
20:27:25	autofocus	NGC 346	L	5s	68	5.55	—
20:27:51	autofocus	NGC 346	L	5s	0	0.00	—
20:28:10	autofocus	NGC 346	L	5s	139	3.64	—
20:28:30	autofocus	NGC 346	L	5s	270	2.74	—
20:28:50	autofocus	NGC 346	L	5s	343	2.47	—
20:29:10	autofocus	NGC 346	L	5s	433	2.13	—
20:29:30	autofocus	NGC 346	L	5s	352	2.47	—
20:29:50	autofocus	NGC 346	L	5s	238	3.28	—
20:30:05	autofocus	NGC 346	L	5s	137	4.25	—
20:30:20	autofocus	NGC 346	L	5s	84	5.44	—
20:30:40	autofocus	NGC 346	L	5s	343	2.44	—
20:36:46	light	NGC 346	S	300s	546	4.13	65%
20:42:01	light	NGC 346	S	300s	628	3.70	74%
20:47:02	light	NGC 346	S	300s	675	3.63	80%
20:53:13	light	NGC 346	H	300s	484	3.59	66%
20:58:13	light	NGC 346	H	300s	652	3.41	89%
21:03:52	light	NGC 346	H	300s	623	3.56	85%
21:08:53	light	NGC 346	H	300s	630	3.53	86%
21:15:06	light	NGC 346	O	300s	468	3.72	69%
21:20:07	light	NGC 346	O	300s	542	3.68	80%
21:21:02	autofocus	NGC 346	L	5s	479	2.07	—
21:21:22	autofocus	NGC 346	L	5s	101	5.31	—
21:21:37	autofocus	NGC 346	L	5s	168	3.73	—
21:21:57	autofocus	NGC 346	L	5s	274	2.89	—
21:22:12	autofocus	NGC 346	L	5s	445	2.16	—
21:22:32	autofocus	NGC 346	L	5s	473	2.12	—
21:22:52	autofocus	NGC 346	L	5s	398	2.46	—
21:23:12	autofocus	NGC 346	L	5s	294	3.09	—
21:23:32	autofocus	NGC 346	L	5s	179	4.07	—
21:23:52	autofocus	NGC 346	L	5s	133	4.84	—
21:24:12	autofocus	NGC 346	L	5s	457	2.18	—
21:30:18	light	NGC 346	O	300s	341	3.97	50%
21:35:19	light	NGC 346	O	300s	391	4.06	58%
21:41:05	light	NGC 346	S	300s	423	3.92	50%
21:46:06	light	NGC 346	S	300s	508	3.87	60%
21:51:42	light	NGC 346	S	300s	325	3.91	39%
21:57:41	light	NGC 346	S	300s	76	4.11	9%
22:03:38	light	NGC 346	H	300s	292	3.96	40%
22:08:39	light	NGC 346	H	300s	430	3.84	59%
22:14:14	light	NGC 346	H	300s	151	3.78	21%
22:19:15	light	NGC 346	H	300s	488	3.86	67%
22:25:10	light	NGC 346	O	300s	243	4.05	36%
22:30:11	light	NGC 346	O	300s	327	3.90	48%
22:31:07	autofocus	NGC 346	L	5s	518	2.12	—
22:31:22	autofocus	NGC 346	L	5s	94	6.23	—
22:31:37	autofocus	NGC 346	L	5s	136	4.62	—
22:31:51	autofocus	NGC 346	L	5s	77	3.79	—
22:32:07	autofocus	NGC 346	L	5s	161	2.67	—
22:32:26	autofocus	NGC 346	L	5s	223	2.04	—
22:32:46	autofocus	NGC 346	L	5s	336	1.93	—
22:33:07	autofocus	NGC 346	L	5s	274	2.37	—
22:33:27	autofocus	NGC 346	L	5s	200	3.09	—
22:33:42	autofocus	NGC 346	L	5s	233	3.90	—
22:33:57	autofocus	NGC 346	L	5s	153	4.90	—
22:34:16	autofocus	NGC 346	L	5s	541	2.02	—
22:40:23	light	NGC 346	O	300s	536	3.76	79%
22:45:24	light	NGC 346	O	300s	360	3.84	53%
22:51:06	light	NGC 346	S	300s	157	3.69	19%
22:56:08	light	NGC 346	S	300s	340	3.60	40%
23:01:22	light	NGC 346	S	300s	680	3.52	81%
23:06:23	light	NGC 346	S	300s	580	3.57	69%
23:12:32	light	NGC 346	H	300s	654	3.64	89%
23:17:33	light	NGC 346	H	300s	674	3.64	92%
23:22:56	light	NGC 346	H	300s	607	3.85	83%
23:27:57	light	NGC 346	H	300s	556	4.05	76%
23:34:19	light	NGC 346	O	300s	480	4.02	71%
23:39:20	light	NGC 346	O	300s	491	3.98	72%
23:44:38	light	NGC 346	O	300s	381	4.33	56%
23:49:39	light	NGC 346	O	300s	356	4.52	52%
23:55:18	light	NGC 346	S	300s	632	4.12	75%
00:00:19	light	NGC 346	S	300s	636	4.11	75%
00:01:07	autofocus	NGC 346	L	5s	615	2.03	—
00:01:22	autofocus	NGC 346	L	5s	133	5.33	—
00:01:37	autofocus	NGC 346	L	5s	222	3.88	—
00:01:52	autofocus	NGC 346	L	5s	347	3.03	—
00:02:07	autofocus	NGC 346	L	5s	532	2.25	—
00:02:27	autofocus	NGC 346	L	5s	554	2.18	—
00:02:47	autofocus	NGC 346	L	5s	534	2.24	—
00:03:07	autofocus	NGC 346	L	5s	390	2.97	—
00:03:27	autofocus	NGC 346	L	5s	306	3.45	—
00:03:47	autofocus	NGC 346	L	5s	171	4.84	—
00:04:06	autofocus	NGC 346	L	5s	100	5.84	—
00:04:27	autofocus	NGC 346	L	5s	516	2.29	—
00:10:33	light	NGC 346	S	300s	779	3.72	92%
00:15:34	light	NGC 346	S	300s	796	3.68	94%
00:21:48	light	NGC 346	H	300s	647	3.77	89%
00:26:49	light	NGC 346	H	300s	645	3.76	88%
00:32:19	light	NGC 346	H	300s	664	3.73	91%
00:37:20	light	NGC 346	H	300s	690	3.65	94%
00:44:13	light	NGC 346	O	300s	538	3.86	79%
00:49:15	light	NGC 346	O	300s	633	3.63	93%
00:54:43	light	NGC 346	O	300s	572	3.77	84%
00:59:44	light	NGC 346	O	300s	613	3.67	90%
01:05:40	light	NGC 346	S	300s	840	3.60	100%
01:10:41	light	NGC 346	S	300s	800	3.72	95%
01:16:14	light	NGC 346	S	300s	826	3.65	98%
01:21:15	light	NGC 346	S	300s	800	3.69	95%
01:27:24	light	NGC 346	H	300s	714	3.60	98%
01:29:22	autofocus	NGC 346	L	5s	567	2.24	—
01:29:42	autofocus	NGC 346	L	5s	283	3.53	—
01:29:57	autofocus	NGC 346	L	5s	450	2.58	—
01:30:12	autofocus	NGC 346	L	5s	613	2.10	—
01:30:32	autofocus	NGC 346	L	5s	634	2.07	—
01:30:52	autofocus	NGC 346	L	5s	480	2.56	—
01:31:12	autofocus	NGC 346	L	5s	370	3.18	—
01:31:32	autofocus	NGC 346	L	5s	237	4.23	—
01:31:52	autofocus	NGC 346	L	5s	166	5.13	—
01:32:12	autofocus	NGC 346	L	5s	147	4.75	—
01:32:32	autofocus	NGC 346	L	5s	666	2.02	—
01:39:56	light	NGC 346	H	300s	636	3.81	87%
01:45:32	light	NGC 346	H	300s	614	3.92	84%
01:50:33	light	NGC 346	H	300s	578	4.07	79%
01:57:21	light	NGC 346	O	300s	493	3.98	72%
02:02:22	light	NGC 346	O	300s	508	3.92	75%
02:08:07	light	NGC 346	O	300s	552	3.77	81%
02:13:08	light	NGC 346	O	300s	529	3.72	78%
02:20:01	light	NGC 346	S	300s	765	3.60	91%
02:25:02	light	NGC 346	S	300s	667	3.62	79%
02:33:37	autofocus	NGC 346	S	300s	494	3.68	—
02:33:57	autofocus	NGC 346	L	5s	114	1.89	—
02:34:17	autofocus	NGC 346	L	5s	28	4.96	—
02:34:32	autofocus	NGC 346	L	5s	35	4.10	—
02:34:47	autofocus	NGC 346	L	5s	45	3.36	—
02:35:02	autofocus	NGC 346	L	5s	60	2.59	—
02:35:22	autofocus	NGC 346	L	5s	85	2.10	—
02:35:42	autofocus	NGC 346	L	5s	84	2.07	—
02:36:02	autofocus	NGC 346	L	5s	70	2.48	—
02:36:22	autofocus	NGC 346	L	5s	51	3.08	—
02:36:37	autofocus	NGC 346	L	5s	29	4.06	—
02:36:52	autofocus	NGC 346	L	5s	21	5.10	—
02:37:12	autofocus	NGC 346	L	5s	74	2.05	—
02:43:24	light	NGC 346	S	300s	251	4.31	30%
02:51:24	light	NGC 346	H	300s	132	4.34	18%
02:59:12	light	NGC 346	H	300s	86	5.15	12%
03:21:22	light	NGC 346	H	300s	5	5.19	1%
03:28:34	light	NGC 346	H	300s	0	0.00	0%
03:39:32	autofocus	NGC 346	L	5s	3	3.67	—
03:39:47	autofocus	NGC 346	L	5s	0	0.00	—
03:40:02	autofocus	NGC 346	L	5s	1	0.00	—
03:40:17	autofocus	NGC 346	L	5s	2	4.17	—
03:40:37	autofocus	NGC 346	L	5s	2	3.78	—
03:40:57	autofocus	NGC 346	L	5s	4	3.53	—
03:41:17	autofocus	NGC 346	L	5s	6	3.09	—
03:41:37	autofocus	NGC 346	L	5s	0	0.00	—
03:41:57	autofocus	NGC 346	L	5s	1	0.00	—
03:42:27	autofocus	NGC 346	L	5s	2	5.35	—
03:42:47	autofocus	NGC 346	L	5s	0	0.00	—
03:43:07	autofocus	NGC 346	L	5s	0	0.00	—
03:43:27	autofocus	NGC 346	L	5s	0	0.00	—
03:43:47	autofocus	NGC 346	L	5s	0	0.00	—
03:44:17	autofocus	NGC 346	L	5s	7	5.06	—
03:44:32	autofocus	NGC 346	L	5s	7	4.41	—
03:44:47	autofocus	NGC 346	L	5s	6	3.80	—
03:45:02	autofocus	NGC 346	L	5s	6	3.41	—
03:45:22	autofocus	NGC 346	L	5s	10	3.12	—
03:45:42	autofocus	NGC 346	L	5s	10	3.07	—
03:46:02	autofocus	NGC 346	L	5s	9	3.39	—
03:46:22	autofocus	NGC 346	L	5s	7	3.77	—
03:46:37	autofocus	NGC 346	L	5s	7	4.02	—
03:46:52	autofocus	NGC 346	L	5s	3	4.41	—
03:47:12	autofocus	NGC 346	L	5s	9	3.01	—
04:05:09	light	NGC 346	H	300s	29	5.87	4%
04:10:11	light	NGC 346	H	300s	29	5.65	4%
04:16:22	light	NGC 346	H	300s	23	8.18	3%
04:25:47	light	NGC 346	H	300s	17	7.12	2%
04:33:00	light	NGC 346	O	300s	0	0.00	0%
04:44:59	light	NGC 346	O	300s	2	7.94	0%
04:57:30	autofocus	NGC 346	O	300s	1	0.00	—
04:57:47	autofocus	NGC 346	L	5s	6	4.19	—
04:58:07	autofocus	NGC 346	L	5s	3	5.76	—
04:58:22	autofocus	NGC 346	L	5s	2	6.31	—
04:58:37	autofocus	NGC 346	L	5s	2	6.06	—
04:58:52	autofocus	NGC 346	L	5s	4	4.85	—
04:59:12	autofocus	NGC 346	L	5s	3	5.07	—
04:59:32	autofocus	NGC 346	L	5s	6	4.11	—
04:59:52	autofocus	NGC 346	L	5s	5	4.25	—
05:00:12	autofocus	NGC 346	L	5s	5	4.52	—
05:00:27	autofocus	NGC 346	L	5s	4	5.13	—
05:00:42	autofocus	NGC 346	L	5s	4	6.02	—
05:01:12	autofocus	NGC 346	L	5s	3	7.14	—
05:01:27	autofocus	NGC 346	L	5s	3	7.15	—
05:01:47	autofocus	NGC 346	L	5s	4	5.70	—
05:02:02	autofocus	NGC 346	L	5s	5	4.62	—
05:02:22	autofocus	NGC 346	L	5s	5	4.20	—
05:02:42	autofocus	NGC 346	L	5s	7	3.87	—
05:03:02	autofocus	NGC 346	L	5s	6	4.05	—
05:03:22	autofocus	NGC 346	L	5s	4	4.99	—
05:03:37	autofocus	NGC 346	L	5s	4	5.33	—
05:03:52	autofocus	NGC 346	L	5s	4	5.74	—
05:04:22	autofocus	NGC 346	L	5s	2	7.83	—
05:04:37	autofocus	NGC 346	L	5s	2	6.93	—
05:04:52	autofocus	NGC 346	L	5s	4	5.52	—
05:05:07	autofocus	NGC 346	L	5s	3	5.91	—
05:05:27	autofocus	NGC 346	L	5s	5	4.23	—
05:05:47	autofocus	NGC 346	L	5s	4	4.68	—
05:06:07	autofocus	NGC 346	L	5s	5	3.91	—
05:06:22	autofocus	NGC 346	L	5s	5	4.20	—
05:06:37	autofocus	NGC 346	L	5s	4	4.98	—
05:06:57	autofocus	NGC 346	L	5s	4	4.80	—
05:13:08	light	NGC 346	O	300s	2	8.80	0%

Star counts come from Hocus Focus detection on each saved sub, tagged with the filter in place at exposure start and the target then being imaged. Frames inside completed autofocus runs are excluded. Still capture times come from the AllSky filenames. All times are local.