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(IAAC) RFC: Developing an observing checklist



Fellow deep-sky observers
I need your advice and observing experience. I'm director of the Astron. Soc. S.
Afr.'s  Deep-sky Section, and am responsible for helping observers develop their
skills. 
Newbies most often feel lost when describing an object, so I've been working on
an  observing checklist to guide their viewing.
One should not slavishly follow checklists - they stifle creativity with a veneer
of  scientific authority. However, such lists do help to ensure that you touch
all bases  and don't overlook something.
What kind of checklists should one use?  I've come up with the following, which
is a  synthesis of ideas from, amongst others, the Herschels, and Gregg Thomson
("Developing  a deep-sky observing form" Deep Sky No 29):
1. General appearance within surroundings.
2. Brightness
3. Size
4. Shape
5. Special criteria, dependent on object type; also: star colours
6. Observer details and personal factors
7. Observing conditions
These categories are detailed below. Your comments, additions and corrections
will be appreciated. 
- - - - - - - - - - - - - - - - 
1. General appearance within surroundings.
- - - - - - - - - - - - - - - - 
a) Overall aesthetic appearance of the object within its starfield
b) Noticeable/prominent field stars/asterisms
- - - - - - - - - - - - - - - - 
2. Brightness
- - - - - - - - - - - - - - - - 
Estimating the magnitude of an extended object is notoriously difficult. If by
brightness  one means surface brightness, then a modified form of the Herschel's
scale could be used:
very high -- high -- above average -- average -- below average -- low -- very low
Or perhaps, brightness should be retained:
extremely bright -- very bright -- bright -- average -- faint -- very faint --
extremely faint
- - - - - - - - - - - - - - - - 
3. Size
- - - - - - - - - - - - - - - - 
Angular size can be estimated more readily than magnitude, so there is no reason
why  size can not be given in angular measure. 
Some observers may, nevertheless, prefer to give a verbal description. I think
this is  OK, as long as it is IN ADDITION to the angular measure. As adapted from
the Herschel's: 
arcsec	arcmin	verbal interpretation
5''		eS -- extremely small
10''		vS -- very small
30''	0.'5	S -- small
60''	1'	average
210''	3.5'	L -- large
600''	10'	vL -- very large
1200''	20'	eL -- extremely large
For objects in the NGC, I found:
open clusters (n = 363)	mean = 12.3',  s.d. = 11.6'
globular clusters (n = 125)	mean = 8.3',  s.d. = 6.1'
planetary nebulae (n = 129)	mean = 0.9',  s.d. = 1.7'
galaxies (n = 7418)	mean = 1.7', s.d. 1.9'
The star clusters are thus much larger than planetaries and galaxies. Sizes for 
all objects ranged between an arcsecond and over a degree. 
Verbal descriptions of open clusters will bunch around the "very large" category,
 with numerous "extremely large" ones. Clusters could be accommodated by bumping 
them up two categories:
arcsec	arcmin	verbal interpretation
30''	0.'5	eS -- extremely small
60''	1'	vS -- very small
210''	3.5'	S -- small
600''	10'	average
1200''	20'	L -- large
2400''	40'	vL -- very large
4800	80'	eL -- extremely large
- - - - - - - - - - - - - - - - 
4. Shape
- - - - - - - - - - - - - - - - 
The general shape may be indicated as follows:
1. irregular
	1.1 irregular, with one or more areas of concentration
	1.2 irregular, without a nucleus or areas of concentration
2. regular
	2.1 round, with (central) concentration
	2.2 round, with (central) concentration, and curved arms radiating outwards;
spiral
	2.4 round, without a nucleus
	2.3 elongated or oval with a nucleus.
	2.5 elongated or oval without a nucleus.
For elongated or oval objects, the degree of ellipticity should be indicated:
very slightly oval -- clearly elongated -- extremely extended into a ray
The ratio of minor to major axis should be estimated, as well as the PA
- - - - - - - - - - - - - - - - 
5.0 Miscellaneous - Star colours
- - - - - - - - - - - - - - - - 
Fred Schaaf, in "Seeing the Deep Sky" gives the following table:
	distinctly blue
	blue
	blue-white
	white
	yellow-white
	light-yellow
	deep yellow
	light orange
	deep orange
	orange-red
	red
Chandler, in an 1888 article in Astronomical Journal, gives
	0 white light
	1 the slightest perceptible admixture of yellow with the white
	2 yellow
	3 yellowish orange
	4 full orange or orange-red
	5 to 10  "increasing shades of intensity up to the nearest approach to 
		pure red light of which we have cognizance in the heavens, exemplified
		nearly by such stars as S Cephei, V Cygni and R Leporis."
What to do about them green stars? I've looked through Admiral Smythe's "Sidereal
Chromatics",  and he's got some wonderful creations in there!
- - - - - - - - - - - - - - - - 
5.1 Open clusters
- - - - - - - - - - - - - - - - 
a) Concentration rating (from Trumpler)
	I detached from background, strong concentration
	II detached from background, slight concentration
	III detached from background, no concentration
	IV not detached
b) Brightness range (from Trumpler)
	1  most stars of nearly the same brightness
	2  medium range in brightness
	3  bright and faint stars in cluster
c) Stellar richness (from Trumpler)
	vp  very poor
	p  poor
	m  medium
	r  rich
	vr  very rich
d) the presence of prominent empty spaces / starless patches
e) is there an obvious central star (what colour is it?) or other prominent
individual stars?  f) do any of the stars have a particular colour?
g) is there a glow of unresolved stars, or perhaps nebulosity?
h) are there clumps/chains of stars?
- - - - - - - - - - - - - - - - 
5.2 Globular clusters
- - - - - - - - - - - - - - - - 
a) size of core versus halo (i.e., the concentration rating)
b) degree of resolution
c) how far out are the outliers?
d) elliptical form?
e) chains of stars?
f) dark lanes / spaces / gaps
- - - - - - - - - - - - - - - - 
5.3 Planetary nebulae
- - - - - - - - - - - - - - - - 
a) central star
b) edge sharp / mottled
c) colour
d) light distribution over disk even / irregular
- - - - - - - - - - - - - - - - 
5.4 Galaxies
- - - - - - - - - - - - - - - - 
a) bright patches; areas of uneven brightness
b) dark lanes/patches
c) other structure
- - - - - - - - - - - - - - - - 
5.5 Gaseous nebulae
- - - - - - - - - - - - - - - - 
a) areas of uneven brightness
b) dark lanes/patches
c) other structure
- - - - - - - - - - - - - - - - 
6. Observer details and personal factors
- - - - - - - - - - - - - - - - 
a) Name
b) Experience
c) Quality/accuracy of this observation
d) Difficulty - how much of a challenge was this object
- - - - - - - - - - - - - - - - 
7. Observing conditions
- - - - - - - - - - - - - - - - 
a) Observing site (name, location)
b) Date (and time)
c) Instrument details (aperture, f, type, quality, eyepiece, magnification,
field, filter) d) Seeing (from Thomson)
	1. The atmosphere is so steady that even stars close to the horizon appear 
		to twinkle only occasionally. Excellent high-magnification views may be 
		obtained of the planets and close double stars.
	2. The atmosphere is very steady with occasional disturbance of
high-magnification images.
	3. The steadiness is good, but with regular air turbulence noticeable.
	4. There is a general loss of fine detail at high magnification.
	5. Twinkling stars are quite apparent, but the twinkling is not rapid. Images 
		are unsharp at medium powers.
	6. Fine detail is lost at medium powers.
	7. Star images show rapid twinkling. They appear disk-like.
	8. Fuzzy images are detectable at low power.
	9. Stars appear blurry and appear to change brightness very quickly.
	10. Atmosphere is boiling. There is a complete loss of detail.
e) Transparency (from Thomson)
	1. This is used to indicate the clearest possible sky. If the atmosphere 
		is `perfectly transparent', then only a slight amount of haze is visible 
		near the horizon.
	2. Indicates a sky that is very clear but not perfectly transparent.
	3. Haze is noticeable toward the horizon, but overhead the sky if perfectly
transparent.
	4. Very slight haze is noticeable overhead near bright objects.
	5. Haze appears overhead, but faint stars are visible.
	6. Obvious haze or thin clouds lie overhead.
	7. The faintest stars typically visible from the site are not visible.
	8. Smoke, haze, or fog limits visibility significantly and creates glare around
bright objects.
	9. At the zenith, absorption limits visibility by one magnitude.
	10. At the zenith, absorption limits visibility by two magnitudes or more.
f) Sky darkness - the level of artificial lighting, moonlight, or zodiacal light
illuminating the sky (from  Thomson)
	1. There is a total absence of moonlight and artificial lighting in the sky. 
		With good seeing and transparency, stars fainter than 6th mag are 
		visible with the naked eye.
	2. Very slight brightening of the sky, like that caused by zodiacal light.
	3. Three-day old Moon or slight light pollution, but 6th mag stars are visible
overhead.
	4. Faintest portions of the Milky Way barely visible.
	5. Overhead appears fairly dark but sky is fairly bright around horizon.
	6. Only the brightest portions of the Milky Way are visible.
	7. General illumination of the entire sky equal to seven-day-old Moon. Faintest 
		stars visible are magnitude 5.5
	8. Sky is bright, similar to a three-quarter Moon.
	9. Sky is very bright; faintest stars visible are magnitude 4.5
	10. Illumination equivalent to, or greater than, the Full Moon.
g) Limiting magnitude (at what altitude observed; assume V mag)
-------------------------------------------------------------------------------
Auke Slotegraaf    :    auke@global.co.za    :    http://www.global.co.za/~auke
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