My Logbook

Everything below was seen from the paddock, mostly through a 10-inch f/5 Dobsonian, unless the notes say otherwise. Times are UT, because local time is useless to anybody who does not live here and UT is the one thing every observer on earth agrees on.

The NELM column is my naked-eye limiting magnitude for that session — how faint a star I could see unaided, which is the honest measure of how dark the sky actually was. If you do not know why that matters more than the telescope, there is an explanation further down this page. The short version: a bigger number means a darker sky, and it is often the more important figure in the row.

March 1999

Loggings, 1–14 March 1999. Times UT, positions approximate. On a narrow screen, scroll the table sideways.
Date	UT	Object	Constellation	Instrument	NELM	Notes
01 Mar	0930	Saturn	Aquarius	10" Dob	5.8	Rings well open. I use it to check the mirror is actually collimated before I believe anything else that night.
02 Mar	1041	UNID variable — "the flicker"	Norma	naked eye	4.4	Held it at about magnitude five, steady over an hour. See the thread.
02 Mar	1130	M83	Hydra	10" Dob	4.3	Hint of spiral structure, more suspected than seen. Sky was milky low in the west, which did not help.
04 Mar	0812	NGC 3242 — "Ghost of Jupiter"	Hydra	10" Dob, OIII filter	5.6	The filter turned a formless blob into a disc with a hint of the inner ring. Worth owning for this alone.
05 Mar	1355	Alpha Crucis (Acrux)	Crux	3" brass refractor	6.0	Split cleanly at low power. This is what the old glass is for, and it earns its shelf space one night like this a month.
06 Mar	2202	UNID variable — "the flicker"	Norma	naked eye	6.1	Unusually strong, close to fourth magnitude. Brightest I have logged it this year.
07 Mar	0655	Omega Centauri	Centaurus	10" Dob	5.4	Resolved to the core. Unmistakable, no filter needed, best globular in the sky and it is not close.
08 Mar	1204	NGC 253	Sculptor	10" Dob	4.9	Elongation obvious, dust lane suspected but not confirmed. Coming back to this one on a better night.
09 Mar	1841	UNID variable — "the flicker"	Norma	naked eye	5.2	Brightening event. Dictated onto tape at the time — see tape_hiss's post on why that mattered more than I realised.
10 Mar	1015	Jupiter and the four Galilean moons	Taurus	90 mm Maksutov	—	All four moons visible, steady air all morning. NELM is not the limiting factor for a target this bright, so I have not bothered logging it.
11 Mar	1320	Eta Carinae Nebula (NGC 3372)	Carina	naked eye	5.0	Keyhole visible without optical aid. Note for anyone doubting a report: this is what an unambiguous detection looks like.
12 Mar	0740	NGC 6752	Pavo	10" Dob	4.0	Right at the edge. I would not have called this without averted vision, and I nearly did not log it at all.
13 Mar	2115	UNID — faint smudge near Norma	Norma	10" Dob	—	Uncertain whether this was real or eye fatigue after two hours out. Left the NELM incomplete on purpose: there was nothing solid enough to rate the night against.
14 Mar	1100	UNID variable — "the flicker"	Norma	naked eye	5.9	Clean naked-eye estimate against two comparison stars. A good night for the watch, and one more data point for the new-moon question.

Fourteen entries this fortnight, of which three are unidentified. That ratio is normal and anybody claiming otherwise is not writing everything down.

How to write an observation report that is worth reading

This is the sticky from the board, kept here because it belongs with the logbook. It applies whether you are reporting a variable-star estimate to a proper archive or just posting what you saw.

The six things a report must contain

Date and time in UT. Not your local time. Not "last night". A reader on the other side of the world has no idea what time zone you are in and will not do the arithmetic for you.
Your instrument and aperture. A report is a claim about what a specific setup could resolve, not about the sky in general.
A magnitude estimate with named comparison stars and the chart used. Not a bare "faint" or "bright" — the step method, comparing against two known stars either side of your target, is what turns an impression into a number somebody else can check.
Seeing and transparency conditions. The aperture argument ran for a week largely because people were reporting what they saw without saying how dark or how steady the sky actually was.
A plain description of what you saw, not what you concluded. "A faint, slightly elongated smudge, no core visible, held steadily with averted vision for thirty seconds" is evidence. "Definitely a galaxy" is not, and a serious observer will not trust it, because it does not demonstrate that you saw the shape rather than talked yourself into one.
Your site. The same telescope in a backyard and in a paddock two hours away can produce reports that look contradictory until you know where each one was made.

The rule underneath all of that

Write down what you saw, not what you concluded. A logbook full of "unid" is a good logbook. A logbook where every faint smudge has a confident name against it is either the work of somebody observing from an extraordinarily dark site, or far more likely, a record of guesses that will be quoted back as fact in four years.

Three of the fourteen entries above are unidentified, and one of them has an incomplete NELM because there was genuinely nothing solid enough to rate the night against. Leaving those gaps visible is the whole discipline.

How we rate the sky: seeing and transparency

Two figures, both older than this hobby's electronic age, and both things a machine cannot measure for you — you have to look up and judge them yourself before you trust anything you saw that night.

The Antoniadi scale for atmospheric seeing.
Grade	Means	You are rating
I	Perfect seeing	No tremor at all, even at high power. Rare, and you remember the nights that had it.
II	Slight undulations	Fine detail holds steady most of the time, with brief moments of calm air.
III	Moderate turbulence	Fine detail comes and goes. Good enough for most deep-sky work, marginal for splitting close doubles.
IV	Poor seeing	Images boil constantly. High power is not worth trying.
V	Very bad seeing	Barely worth setting up. Some nights you pack it in.

NELM — naked-eye limiting magnitude — is the faintest star you can see unaided, checked against a chart of known comparison stars near the zenith before you start observing. It is the honest number for how dark your sky actually is that night, independent of what telescope you own. A quiet suburb might give you NELM 4 to 4.5; a genuinely dark rural sky can reach NELM 6 or better.

Worked example, from the aperture thread. The same telescope, the same targets, two sites. In a light-polluted backyard: NELM 4.2, ten-inch Dobsonian, four galaxies found. At a dark paddock two hours away: NELM 6.3, the same ten-inch Dobsonian, most of the target list visible. Same aperture, same mirror — the number that changed was the sky, and it explains the whole disagreement.

Unverified backyard reports — cross-check against a proper almanac before citing anything here as observational data. Best viewed in Netscape Navigator 4.0 at 800×600.