© Ciel
Extrême, 1998
|
DRAWING THE DEEP SKY
to be rolled down
|
© Yann
POTHIER, 1997.
article published in Pulsar (SAP)
NGC
1023 - J. CRESPIN, T200, F/10, G=200x
SINCE WHEN ?
The benefits of drawing in the deep sky are numerous and all "aficionados"
agree to that (BENECK, Astro-Ciel no13; THOMPSON, Pulsar no660). Nevertheless,
this recording method is not widely used by amateurs... Why ? The "affair"
of martian's canals "imagined" by SCHIAPARELLI and LOWELL about
1877 is without doubt at the origin of the decline of the astronomical
drawing as a good observation recording method. Moreover, the rapid flourishing
of photography after 1890 contributed heavily to the drawing's disgrace.
Let us insist on the fact that generations of well known observers were
also deep sky drawers (MESSIER, ROSSE, D'ARREST, etc.) and that drawing
was at the origin of scientific production of the 17, 18 and 19th centuries.
NGC
6826 - V. LE GUERN, T760, F/4.1, G=867x
WHY ?
It's a fact: deep sky drawing is back to fashion among amateurs astronomers,
notably in deep sky observing but also for planetary and cometary amateur
work. Deep sky drawings are allowing direct comparisons of observers, instruments
and observing sites. The drawings have the undeniable advantages of focusing
the observer's attention on the details appearing on deep sky objects and
to constrain the observer to spend more time at the eyepiece. Thanks to
the drawing, the eye becomes a searching tool and this method avoid marathon-like
observing.
Drawing is a true educational process, teaching the amateur not
only to see but to observe. This can lead novice observers who see
two belts on Jupiter, at best Cassini's division, no details on comet tails
and less on nebulae, to concentrate on planets nodosities, cometary ejections
and darks bands on edge-on galaxies. Some says "A photography never
lies"; it is true that a drawing can suffer from the subjectivity
of the observer... However, deep sky photography never gives a fair rendition
of reality because of spectral differences of receptors (maximum sensibility
at 4300angstroms for photography versus 5000 for the eye's rods in night
vision).
Of course, drawings are poorer than photos and CCD images in detail,
above all in the fainter parts that are well shown on deep exposures. Even
so, the eye can do a remarquable job on bright areas often overexposed
on photos and images (unless unsharp masking or multiple addition is done
- still rare thses days).
NGC
6934 - P. CHATARD avec T400 à F/6 & G=96x
One must take in account the financial investment represented by recording
methods. The price of a drawing will always be a hundred times less
than that of a camera (photography or CCD). Furthermore, a long period
separates the photographic exposure from the developpment (less time in
case of CCD imaging) but the drawing produces immediate results: the observer
is able to correct in real time the errors without having to wait for another
clear night to start again. No more frustration for the newcomers equiped
with an azimutal mount: drawing is easy with or without equatorial tracking
!
Let's cut short any tedious debate: for the amateur astronomer, there
is no need to find a world champion method, but to find the
world champion method for the type of observing planned. In visual
observation of the deep sky, the drawing is (to my opinion) the best method.
The deep sky sketcher will watch out not to be affected by memory images
(those detailed magazines prints). There is no need to repeat other observer's
observations but rather to see an object for yourself and give your personnal
vision of the object.
Let us conclude these arguments by insisting on the fact that no artistic
ability is required for this task. You know how to draw a point and a nebulous
patch ? Well, it is all you need...
HOW ?
The deep sky sketcher will prefer to be seated at the telescope and
still have access to the eyepiece (tiredness is always a problem). This
position is better and one can lay a drawing board on the upper leg. Everyone
can build a cheap drawing board adapted to its needs and usage. A very
faint light (red or else) will illuminate the board.
Palomar
11 - Y. POTHIER, T450, F/4.5, G=222x
One can choose to draw in black on white paper of in white on black
paper. The former is easier to do and a copy of the drawing can be made
later in white on black if needed. The "black on white" method
stands better the rubber erasing, so we will concentrate on this way of
drawing.
Choosing the pencils are important and I recommend a fat and sharp
mine (diam 0.5mm) pencil to trace the stellar dots, and two pencils one
fat and one dry to draw nebulous area and shadings. The rubber will need
to be white and soft in order to leave no trace and could be grind thin
for small erasing.
You can choose the drawing sheet of your choice with the info you find
useful. It must contain a drawing area preferably round representing the
observed field with a diameter comprised between 100-75mm for wide fields,
75-50 for medium fields and 50-25mm for small fields. This circle may represent
the full field or a comfortably smaller area in the field given by the
eyepiece. In both cases, in order to obtain a good object size, he must
be 10-20% of the field.
A free area next to the circle will be left for data about the observation:
A) object's name and reference (catalogue) + type (cluster, galaxy,
nebula, ...).
B) instrument, F/D, amplification used
C) scale and orientation
D) conditions of transparency, seeing, objects elevation above horizon.
E) any comments or details impossible to draw
Once the drawing sheet is set, duplicates (photocopies) will be made
and tested in the field. For myself, I use a 10.5x9.9cm sheet (21x29.7cm
page divided in 6) with a 7.2cm diameter circle. Humidity can soak the
paper and reduce the possibility to sketch... A solution is to install
a removable plastic cover over the drawing board.
WHICH STEPS ?
I propose the following steps to achieve a correct drawing (proposed
by numerous dedicated observers). These chronological steps are facilitating
the sketcher's task and are helping to organize oneself.
|
0= watch the field for some time before starting to draw
to memorize it and the principle details, as well as to center it the way
you want to reproduce it. |
 |
1= draw the brightest stars and the one bordering
the field you want to reproduce. |
 |
2= draw the other stars (fainter and fainter
ones) all over the field (except the ones very near the object) by simple
alignments or geometric shapes (triangles, squares, etc.). |
 |
3= draw the outline of the object thanks to
the stellar background with a fat pencil if it is a bright object or a
dry one if it's a faint one. |
 |
4= brush gently the object's trace with a
rag or a clean finger in order to give the object its nebulous and homogeneous
look . |
 |
5= with a thin rubber, define the edges of
the object (if they are sharp) and place dark areas (if there appears some);
add with a dry pencil any brighter knots or patches on the object. |
 |
6= find the field orientation and determine
the scale (see Astro-Ciel no55 for more details); these indications are
more accurate if determined at the end of the drawing process. |
Some more advices:
- star brightness can be drawn by two methods: wether you choose
to draw different star diameters (to the risk that a very bright star will
look like a big black circle) or you choose to push more or less your pencil
on the paper (a darker patch is a brighter star); I have choosen the former
way of indicating stellar magnitudes but one can decide not to pay attention
to it and adopt a very small stellar circle scale, proposing an aesthetic
drawing but not an informative one.
- for the larger nebulous objects (big galaxies and gaseous nebulae),
some reference stars must be sketched around the object location and some
pencil markings are to be brushed for the nebulous aspect (classical method
as described above). In the end, internal stars will be placed on the nebulous
outline with the further internal details (they would have been "nebulized"
by the brush process otherwise.
- for galaxies, the pencil markes to be brushed are to be placed
in the core's place (if there is one); the outer halo will be brushed from
this initial deposit.
- for globular clusters, in case of nebulous background caused
by unresolved stars, the brush process must be done first to create the
globular's halo before star plotting in the drawing and those resolved
on the cluster (otherwise sharp stars could be blurred).
- for filter observing of nebulae, it is easier for the fainter
objects, once located with filter, to draw the stellar field without it
in order to plot the faintest stars (vanished with filter) before drawing
the nebula thanks to the filter.
The deep sky sletcher must be aware of its own limits and will see
to avoid inventing details and should take care of sketching only the details
seen for sure. Doubtful or fleeting details will be indicated clearly in
the comment section of the drawing sheet (eg. details seen 50% of the time).
M
13 - D. PONSOT avec T200 à F/6 & G=300x
CONCLUSION
Let's repeat it again: no need to be an reputated artist to become
an experienced deep sky sketcher. Apart from this, even if you don't have
access to a huge telescope or pristine skies, each drawing has its value
for calibrating both the observer, his site and instrument, and this three
factors are always forming a unique combination for each amateur.
Your drawings are of interest for Ciel Extrême's readers and
you can send them at the following adress:
Yann POTHIER - Ciel Extrême
11 Impasse Canart
75012 PARIS
M
42 - L. BILLARD, T450, F/4.5, G=62x
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