|
Related Links
Feitzinger Dark Nebulae
Barnard's Dark Nebulae
How do I create my own unique symbol?
What is an SDB file?
TheSky Database File here is a
slightly revised version (created December 2005) of the Lynds Dark Nebula catalog
when compared to that supplied with
TheSky5/6 and as found
on the DataPlus CD.
The original source for the newer dataset follows.
The CDS Service for astronomical Catalogues
The CDS
FTP SITE:
http://cdsweb.u-strasbg.fr/viz-bin/qcat?lynd
NOTE: I chose to create a new field
denoting the size of these objects as a circle representing the approximate
size
of the objects in arc minutes on the main TheSky display. This
addition becomes the very first field in the
data moving the above columns over to the right to make room.
By taking the size of the object given in
square degrees I used the following method (in Microsoft Excel) to generate a circle of approximate
size so the objects would plot accordingly.
radius = Square Root (size in square
degrees/PI).
To convert degrees to arc minutes multiply by 60 arc
minutes/degree. Then take the radius times 2 = diameter in arc minutes.
Then assign the size in arc minutes to the MAJOR and MINOR Axis in the
header and you have a circle.
Example:
Take 1.2 square degrees from the data for record #2. The conversion yields a circle of
75 arc minutes in size or ~1.2 square degrees.
;copyright Software Bisque 2005 http://www.bisque.com
>SEARCH 14,19 <----------Columns 1-4 shifted by adding size field
>RAHOURS 20,21
>RAMINUTES 23,26
>DECSIGN 30,30
>DECDEGREES 31,32
>DECMINUTES 34,35
>MAJOR AXIS 1,13
>MINOR AXIS 1,13
>PARSE "Original Catalog Number" 14,19
>PARSE "Galactic Long/Lat" 39,49
>PARSE "Area (sq degs)" 51,57
>PARSE "Opacity (1-6 / 6=darkest)" 59,59
>PARSE "Identification Number" 60,63
>PARSE "Sequence number" 64,68
>PARSE "Barnard" 76,110
>PARSE "Lynds2 " 71,73
>IDENTIFIER LDN
;The CDS Service for astronomical Catalogues
;http://cdsweb.u-strasbg.fr/viz-bin/qcat?lynd
>OBJECT TYPE 16
;16 = Dark Nebulae
>LOADMEMORY
Because the text file has been compiled using
a field to "SEARCH" for specifically columns 14-19 as explained above, the data can be
searched in TheSky using
the find dialog (Edit | Find). You must precede the Find entry with
LDN then enter the Lynds NUMBER you wan to search for.
Example: Find LDN 1622
returns the following:
Object name: LDN: 1622
Magnitude: 0.0
Equatorial: RA: 05h 54m 23s Dec: +02°00'18"(current)
Equatorial 2000: RA: 05h 54m 36s Dec: +02°00'29"
Horizon: Azim: 198°38'15" Alt: +50°47'49"
Visibility: Rise 17:05, Set 05:26
Transit time: 23:14
Source catalog: Sky Database: LDN
DB field 1: Original Catalog Number: 1622
DB field 2: Galactic Long/Lat: 4.53 -11.67
DB field 3: Area (sq degs): .122 <--------Equals
23.6 arc minutes!
DB field 4: Opacity (1-6 / 6=darkest): 6
DB field 5: Sequence number: 1616
DB field 6: Identification Number: 107
DB field 7: Barnard: 107
DB field 8: Lynds2 : 351
Edit | Find LDN NUMBER to
search
Each entry from the SEARCH field listed
If you wish to have each object
centered for you and the Object Information displayed as you scroll down the
list just place a check in the Frame Object and Object Information boxes as
shown above.
Recompiling the data is quite
simple BECAUSE the header does all the work for you! If you wish to
change the Search field, or the order of the fields shown in the Object
Identification dialog feel free to do so.
Make any changes you want then just use Data | Import and Browse the text file
by name on your local drive and press the "COMPILE" button highlighted
below.
Warning!
See the Epoch 1950 note below.
Data | Import
Then press Compile
To label the fields use View | Display
Explorer and EXPAND the "LDN" entry under Sky Databases (SDB's) as
shown below. There you can place a check mark next to the
fields you wish to have labeled on the screen.
Pick fields you want to show
View | Display Explorer
Next make sure the "EXTENDED
LABELS" are set to "visible" AND secondly make sure the Object Type Dark
Nebula is also enabled. View | Labels | Extended Labels for labels and
View | Display Explorer | Dark Nebula is set to visible.
Keep in mind that enabling several
fields at once clutters the screen.
View | Labels | Extended Labels
Make sure they are checked!
Also enable Dark Nebula
Make sure Dark Nebulae are visible
Lastly. Use the Display Properties for Dark
Nebulae to set the Font type, size, color, nebulae fill color, etc.
See below.
View | Display Explorer | Display Properties
Choose what suits you!
The following is near the star
Antares in the constellation Scorpious. Note the approximate size of
the Dark Nebulae and their labels are shown!
Wow, cool!
14 degree Field 16h 40m 17.8s -29d 16m 44s with labels
Because the data used
Epoch 1950
as described above in the field definitions section this needs to be used when
compiling the data. Using Epoch 2000 will cause a slight discrepancy in
the positions of the objects.
And now consider this. Following is a
chart showing the entries from the Lynds' Dark Nebula and also the data from the
catalog of Barnard's Dark Nebula for comparison. It should be noted that
very few, if any, datasets out there today are 100% perfect.
Lynd's and Barnard's Dark
Nebula
click on image for Hires full size
Note discrepancies!
The green labels and turquoise
circles are the Lynds data, yellow labels and blue circles are the Barnard
entries, and the label Snake Nebula is my own entry. These kinds of errors
(positional, magnitude, and/or size errors) are quite common in many of the
datasets that exist.
Catalog Capriciousness
<---- Click here
for a complete synopsis on-line reprint of a very
informative article by Stuart Goldman of
Sky and Telescope magazine.
The following excerpt is taken
from the README file,
VII/7A Lynds' Catalogue of Dark Nebulae (LDN) (Lynds 1962)
================================================================================
Catalogue of Dark Nebulae
Lynds B.T.
<Astrophys. J. Suppl. Ser. 7, 1 (updated version) (1962)>
=1962ApJS....7....1L
================================================================================
ADC_Keywords: Nebulae
Description:
This catalog is an updated version from the published version. The
catalog was based on the red and blue prints of the National
Geographic - Palomar Observatory Sky Atlas. The catalog contains
positions, both equatorial and galactic for the centers of dark
nebulae. Values for the cloud sizes are given in square degrees, and
estimates of their opacity are given. The updated catalog is ordered
by galactic longitude and includes cross references to the published
catalog and Barnard Object numbers associated with the clouds.
The field information used for the data is detailed here,
Byte-by-byte Description of file: ldn
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- LDN *[1/1802]?+ Catalogue number from
original published version (ApJS 7, 1)
6- 7 I2 h RAh Right Ascension 1950 (hours) of Cloud Center
9- 12 F4.1 min RAm Right Ascension 1950 (minutes)
16 A1 --- DE- Declination 1950 (sign) of Cloud Center
17- 18 I2 deg DEd Declination 1950 (degrees)
20- 21 I2 arcmin DEm Declination 1950 (minutes)
23- 28 F6.2 deg GLON [0/360[ Galactic longitude of Cloud Center
30- 35 F6.2 deg GLAT Galactic latitude of Cloud Center
37- 43 F7.3 deg2 Area Area, in square degrees, of the Cloud
45 I1 --- Opacity *[1/6]?=0 Opacity class
47- 49 I3 --- ID *[0/416] Identification Number.
51- 54 I4 --- Seq [1/1791] Running Number in this version
of the Catalogue (ordered by GLON)
56- 59 I4 --- Lynds2 *Number that B. Lynds assigned when
the updated catalogue was created.
61- 92 A32 --- Barn *Cross-identifications with Barnard Objects.
(up to 8 Barnard numbers in format 8A4)
See the above
HEADER TEXT showing how to use these field with
the SDB header that allows immediate compiling of the text.
|
