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ASTRNOMY
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DIFF_DRA.ZIP
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1993-05-10
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3-D DIFFRACTION DRAWING PROGRAM
This program will display a three dimensional representation of a binary
star system. The program will run on systems with VGA , EGA or
Hercules graphics cards. The BGI files which come with the programs are
essential for the correct running of the program and should not be removed.
The 3-d representation that is displayed indicates intensity
in the z (vertical) direction and the x-y (horizontal) plane represents the
background plane of the celestial sphere.
Where the program prompts for multiple inputs they should be typed in
separated by at least one space, or alternatively one at a time following by
the return key.
The programs uses the following parameters to calculate the representation
A)
I) The aperture of the telescope being used. (In millimeters)
II) The separation of the primary star from it's companion (comes)
(In arcseconds)
III) The magnitude(brightness) of the primary star. If unsure about this
term contact any good astronomical reference book.
IV) The magnitude of the comes
V) The vertical exaggeration. This parameter is useful when faint detail
is wanted such as in the case of an unequal binary pair.
B)
Taking skyglow into consideration
This parameter can be useful when determining what the system looks like
in reality compared to that predicted in theory. The parameter asks for
magnitude difference between the primary and the faintest start in the
vicinity of the system. This can be useful if the system is being observed
from somewhere where there is skyglow, such as in a city.
To see how it affects the display try typing in a value that means
that the sky is just fainter that the comes.
Try these values for the famous Ursa Major Binary star system :
Magnitude
Primary : Alcor 3
Comes : Mizar 5
Then try the following parameters for skyglow
6 : For an almost perfectly black background OR
3 : For a area which suffers badly from light pollution
C)
This just asks for the name of the system so that it can be displayed
on the screen.
D)
This option can be used to simulate the type of telescope that is being
used. If you answer no (n) then the program will assume that you are using
a refractor type telescope and will start to draw the representation
immediately.
If on the other hand you answer yes (y) then the program will
assume you are using a reflector type telescope which has diffraction
resulting from a spider mount being in the optical path.
Then two more questions will be asked as follows
I)
The spike angle :
This is the angle between successive diffraction spikes.
In a reflector type of telescope a device called a spider is used to
deflect the optical but because of this, it also introduces
diffraction effects. Different shapes of spiders introduce different types
of diffraction as shown below.
Diagram of Spider shapes
│ │ │
│ │ │
│ │ │
│ │ │
────────┼──────── │ │
│ / \ │
│ / \ │
│ / \ │
│ / \ │
(1) (2) (3)
The first shape causes a 90 degree diffraction effect, the second
shape causes a 60 degree diffraction effect (note: not 120 degrees),
while the last one causes a 180 degree diffraction. Other values can also
be envisaged but they must be a fraction of 360 degrees.
II)
The angle between the spike and the line joining the two stars
measured in a clockwise sense.
This parameter is used to enable the diffraction effects to be rotated to
any desired angle. This is necessary as the earth's rotation causes this
angle to vary and so it must be allowed for. This value cannot be easily
calculated and can be obtained from observation at the instant in question.
NOTE:
The program won't work unless it has access to the .bgi file's which
accompanies it.
If you find this program useful please send a donation to the author to help
in producing updates.
For more information please contact :
P.J. Naughter,
Cahore,
Ballygarrett,
Gorey,
Co. Wexford,
Ireland.