The Trapezium
Related links
Additional SDB
files back to
Instructions
for adding SDB files to TheSky
Understanding Catalog
Capriciousnessfs
In the past I was frequently asked why
TheSky does
not contain the 4 to 6 primary stars in the "Trapezium" a well known
"asterism" of stars located in the heart of the Orion Nebula M42
- NGC1976 in the constellation Orion
so an explanation is in order.
The issue does not have to do with TheSky's
ability to plot stellar data accurately, nor does it have any thing to do with
zoom level
limitations (as other competitor's have falsely claimed in the past), but
rather with the common stellar catalogs currently available to all planetarium
programs.
The four common Trapezium stars are not in included in the GSC data, SAO data, USNO A2.0,
UCAC2, or the Hipparcos/Tycho-2 data. Only after plotting the
USNO-B1 80 gigabytes of data containing 1 billion stars do the four
common stars show. And there are actually more than just the 4 brighter
stars in close proximity
To address the problem of the missing stars
Software Bisque as added them using
TheSky's Database Manager, and has done so for many years (20+), using
auxiliary data
input. In fact, this same method is currently been used by
most competing planetarium programs now to fill in the missing Trapezium stars.
Download the above files and extract them
into the default SDB folder,
..\Program Files\Software
Bisque\TheSky6\Data\User\SDBs\
In TheSky
you can
zoom into a field of view as small as 1 arc-minute across the screen. Take the one
arc-minute field divided by your screen resolution in pixels and you have
the resolution in arc seconds/pixel. For example, a screen resolution
of 800 by 600 yields a resolution of 0.075 arc seconds/pixel!
For even more stellar data TheSky also
supports the US Naval
Observatory data on a single CD-ROM of 54 millions stars or 11 CD-ROMS
containing 526 million stars and now the
USNO-B (subset as distributed
with TheSky) and the UCAC2 stellar catalog. Provided you have the
entire 80 gigabytes with 1 billion stars USNO-B1
complete to ~21 magnitude
these too can be plotted in TheSky.
Because 80 gigabytes is far
too much data to re-distribute with TheSky a
subset version was carefully created to fit the needs of most if not all
of TheSky
users.
CCD
image
(c) Mike Palermitti, Jupiter FL
click image for animation
The following screen shot
shows TheSky version 6 display with
1.5 billion stars plotted from the USNO-B, USNO A2.0, GSC,
Hipparcos/Tycho-2, and UCAC 2.0 data.
Note: Yes, their is redundancy
between catalogs as well as discrepancies in position and/or magnitudes.
What's with the arrow on
the middle star?
If you enable the option to plot those stars that have proper motion
data a vector line is drawn indicating direction and amount of motion over
the time you specify. Also see the page
Barnard's Star for more details
using the highest proper motion star for more!
Following are the additional stars
found in the "Trapezium" SDB file included with the latest update to
TheSky6
CLICK HERE to
get the most recent update to version 6.
Note the Trapezium stars are not loaded by default. The Trapezium
Stars need to be added to the Active List of databases using the Data | Sky
Database Manager | Add/Remove option. Step-by-step
instructions here.
More Stars added
Now the display looks more like the real thing!
(is it live or Memorex?)
The Trapezium data file (SDB) is located
in the folder
..Program Files\Software
Bisque\TheSky6\Data\User\SDBs\trapezium.sdb
along with many other SDB files you
can add to the list. Please
see the following URL for a description of SDB files and how to add them
to your current list.
What is an SDB
(Sky DataBase)
file? or refer to TheSky's manual.
In addition to the error prone
and somewhat obsolete now GSC
data TheSky6 is now using the Hipparcos/Tycho, UCAC, and USNO-B (a
distributed subset of the 80 gigabytes with 1 billion stars) catalogs or
any combination. Since all of the SAO catalog of 259,000 stars
are
included in other stellar catalogs we do not have these redundant data
entries but this stellar data is cross referenced to the other stellar
catalogs.
For those that wish to plot the
SAO catalog I have created
an SDB file
that allows these stars to be plotted and searched as well. Click
here for details on using
TheSky Database
files (SDB'S).
The Hipparcos/Tycho catalogs are
much more accurate in regard to stellar positions (including proper
motion) and magnitudes when compared to the now dated GSC data. However,
even the Hipparcos/Tycho data contains only a handful of stars ~1 million between,
and as with all large data sets even this widely claimed near perfect data
is now being found to contain certain many entry errors. Note that it is
extremely difficult to maintain any database with thousands of objects
like the NGC data or
even millions of positions and magnitudes like the Hipparcos/Tycho, GSC, UCAC, USNO-B, USNO A2.0, data.
For additional datasets like the Yale
Bright Stars or the SAO catalog see the following.
The method used to create the G)uide
S)tar C)atalog
data was to scan the actual photographic plates and create entries for the
stellar positions and magnitudes as seen by the scanning method and
complex pattern recognition software designed for the task. This
would have not been possible or realistic to have humans do the tedious
and arduous task, not to mention that would still be prone to errors!
The
GSC stellar data is used by the
Hubble Space Telescope for orientation
purposes. Note that many of the stellar and non-stellar catalogs
that we choose to use in TheSky, yes even the NGC catalog, contain
positional errors, magnitude errors, size errors, and even missing
data. To this end there was an article written by Stuart Goldman editor of
Sky and Telescope regarding these types of catalog errors.
The well written article titled "Understanding Catalog
Capriciousness" printed in Sky and Telescope magazine can be found
reprinted with permission here.
To explain the missing stars in
the Trapezium let us first show the actual digitized image of the Great
Nebula in Orion M42/NGC 1976 found on the digitized Sky Survey
photographic plates.
Digital Image of
M42
Created in CCDSoft
from the 102 CD-ROM of the Palomar Sky
Survey
RealSky/DSS Copyright
Since most of us cannot afford the
complete 102 CD-ROM set the Space Telescope Science Institute and the Astronomical Society of the Pacific have
made this data affordable and manageable. The compressed 18 volume
set of the data known as RealSky (8 CD-ROMS northern Hemisphere and 10 CD-ROMS for the
southern). Unfortunately this product has been discontinued and all
our requests to obtain the rights to re-distribute the data have gone
unanswered.
Using the DSS or RealSky data you have the entire night sky as seen with a 48"
telescope complete to 19th magnitude at your finger tips. When RealSky is used in conjunction with TheSky you have a
very powerful research tool that can overcome the problems related to
cataloged data. Looking at the above image it is easy to see why the
normal means of creating data from the plates was susceptible to
problems. Take another example, M13 the Great Cluster in
Hercules.
Globular Cluster
M13
Created in
CCDSoft
from the 102 CD-ROM of the Palomar Sky Survey
RealSky/DSS Copyright
Based on the images above you can
see why there are holes in the bright tight globular clusters or missing
stars in the areas where there is a lot of nebulosity. There are
some areas like M42 the Great Nebula in Orion or M22 the Globular Cluster
in Sagittarius where other methods have been used to fill in the hole of
missing stars.
Frankly I was surprised to find that out of
the USNO data (550 million stars), SAO data, the GSC data (1.1 and 1.2) data, and the
Hipparcos/Tycho-2 data there still aren't all entries for the common 4 to 11+
stars in the Trapezium. The reason I created my own entries for
these stars was I have not found a good source for them.
By using an on-line source like the astronomical database
Simbad or the
NASA Extragalactic
Database you can make a query using M42 for the search criteria and
request say all stars within 10 arcminutes of the object. Cool!
NOTE: If the objects to
be compiled are of type stars instead of say object type "reference point"
the use of the
magnitude is crucial. I have seen datasets that don't have magnitudes only
coordinates. Plotting stars that do not have
magnitudes associated with them indicates a magnitude zero!
The stars that all have a zero
for magnitude will plot extremely
large and look completely unrealistic because of this. Better to use object
type
Reference Point when compiling the data or create your own custom symbol
<--- Click here which is magnitude
independent and unique.
To demonstrate. The
Trapezium in the center of M42 the Orion Nebula asking for all objects
within 5 arc minutes of the objects Plotting the data query from the
NASA Extragalactic Data page we get the
following when the object type is "star" before compiling the dataset.
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