OF THE ROGER N. CLARK

VISUAL ASTRONOMY OF THE DEEP SKY
Table C.2 (cont. )
2300 REM ** ******** cosineHA
2301 REM subroutine to compute the cosine of the zenith angle when the
2302 REM object is at the ho rizon = COSHA
2305
2307 X#= SQR(l#-COSHA# *COSHA# )
2308 IF X#=O ! THEN X#=lE+37
2310 HAHORZ# = PIHALF# - ATN (COSHA# /X#)
2315 RETURN
2400 REM ** ******** set time
2401 REM subroutine to compute the set time of an object
2402 REM
2405 REM
2410 TSET# (RA# + HAHORZ# + LONGR# )/(2#*PI#) - SOU
2415 RETURN
2450 REM ********** risetime
2451 REM subroutine to compute rise time of an object
2455 TRISE# = (RA# - HAHORZ# + LONGR# )/(2#*PI# ) - SOU
2460 RETURN
2500 REM ** ******** refcorr
2501 REM subroutine to compute refraction corre ction to zenith angle .
2502 REM
2503
2505
25 10
25 12
25 15
2517
2520
2550
2551
2552
2555
2560
COSHA# =(COS (ZH#) - SIN( LATR# )*SIN( DEC# » /(COS (LATR#l*COS ( DEC# »
note ra , hahoriz, longr are in radians , sO in decimal days
REM the following computes the arcsin of (0.9986sin(0.9967za»
X# = .9986047 * SIN( .9967614 * ZA# )
X# = ATN( X# /SQR(l #-X#*X# »
XTMP# = -1 !* PRESSURE * .0571716 /(273! * TEMPC )
XCORR# = XTMP#*(ZA#- X# )*ONERAD#- .000579084#*ZA#*ONERAD#
ZCORR# = ZAP + XCORR#/ ONERAD#
RETURN
REM ** ******** Altitude
REM su brou tine to compute altitude in decimal degrees
REM
ALT# = (ZH# - ZCORR# )*ONERAD#
RETURN
2600 REM ** ******** Az imuth
2601 REM su broutine to compute azimuth in decimal degrees
2602 REM
2603 Xl# = -l#*COS( DEC# )*SIN(HA# )
2605 X2# = COS ( LATR# )*SIN(DEC# ) - SIN(LATR# )*COS (DEC#)*COS(HA# )
2606 IF X2# = O! THEN AZIM# = 0# : RETURN
2607 X# = ATN( Xl#/X2#)*ONERAD#
2608 IF X2# > 0# AND Xl# < 0# THEN AZIM#
2609 IF X2# > 0# AND Xl# > 0# THEN AZIM#
26 10 IF X2# < 0# THEN AZIM# 180# + X#
2620 RETURN
2650 REM ********** Airmass
26 51 REM subroutine to compute air mass of an object
26 52 REM
2655
2660
2661
36011 + X#
X = I! / COS(ZCORR# )
IF ZCORR#= 1.3089 THEN AIRMAS = 3. 7978 + XTMP * 120
2667 IF ZCORR# > ZH# THEN AIRMAS=999 !
2670 RETURN
X#
a
altitude
azimuth
B
C
Cl
D
Appendix D
Symbols and their definitions
The angular size of the telescope's
diffraction pattern in arc-seconds.
(Chapter 3)
The maximum apparent field of
view seen in an eyepiece. (Chapter
3)
The apparent diameter of an object
as viewed by the human eye.
(Chapter 3)
The angular diameter of the diffraction
disk in the telescope, defined
as the diameter where the
light falls to zero in the first dark
ring of the diffraction pattern.
(Chapter 3)
The true angular diameter of an
object in the sky. (Chapters 3, 5)
The angular height of an object
above the local true horizon.
(Appendix C)
The position angle of an object
counting around the horizon; 0°
when due north, 90° when due east,
180° when due south, and 270°
when due west. (Appendix C)
The amount of light absorbed by
the atmosphere, in stellar magnitudes.
(Appendix C)
The surface brightness of an object.
(Chapters 2, 6; Appendices E, F)
The surface brightness of the background
around an object. (Chapters
2, 6; Appendices E, F)
The contrast between an object and
its background. (Chapters 2, 6;
Appendices E, F)
Logarithm of the contrast between
the main surface brightness of an
object and sky background of 24.25
magnitudes per square arc-second.
(Appendices E, F)
The diameter of a telescope objec-
tive or primary mirror. (Chapters
3, 4; Appendix F)
De The diameter of the fully dilated
human eye, usually taken to be ab
out 7.5 millimeters. (Chapter 4)
Dec The declination of an object.
(Chapter 3; Appendix C)
Dec The difference between two declinations.
(Chapter 3)
ep The diameter of a telescope's exit
pupil. (Chapter 3)
j The focal length of an eyepiece.
(Chapter 3)
jm The maximum usable focal length
of an eyepiece. Larger than this, the
apparent field would be restricted
by the eyepiece tube assembly.
(Chapter 3)
F The effective focal length of a telescope.
In simple reflectors or refractors,
this is the focal length of
the lens or primary mirror. In compound
systems, it is the focal length
of the primary times the magnification
of one or more secondaries.
(Chapter 3)
GMSTO the mean sidereal time at Greenwich,
England, calculated for 0
hours UT on a given date. (Appendix
C)
h The observer's elevation above sea
level in feet. (Appendix C)
HA The hour angle of an object from
the local meridian. (Appendix C)
HA' The hour angle of an object on the
horizon. (Appendix C)
JD Julian Day. (Appendix C)
k The atmospheric absorption per air
mass in stellar magnitudes.
(Appendix C)
K The number of J ulian centuries
from 12:00 UT January 1, 2000. A
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