HP 42S/DM42S/Free42: Atmospheric Refraction
Introduction
The program ATREF calculates the atmospheric refraction and the true "airless" altitude of a light from a star or any atmospheric object due to the Earth's atmosphere. As a result, the true altitude is generally lower than the apparent altitude.
Jean Meeus' "Astronomical Algorithms" (see source below) presents an approximation of calculating refraction by G.G. Bennett (University of New South Wales):
R = 1/(tan h_0 + 7.31/(h_0 + 4.4))
where:
R = atmospheric refraction, in arc minutes
h_0 = apparent altitude (the altitude you see), in hours-degrees-seconds format (HH.MMSSSS)
True altitude, in hours-degrees-seconds format (HH.MMSSSS) is calculated as:
h = R - h_0
HP 42S/DM42/Free 42 Program ATREF
00 { 74-Byte Prgm }
01▸LBL "ATREF"
02 DEG
03 "APP ALT?"
04 PROMPT
05 STO 00
06 →HR
07 ENTER
08 ENTER
09 4.4
10 +
11 1/X
12 7.31
13 ×
14 +
15 TAN
16 1/X
17 STO 01
18 "REF: "
19 ARCL ST X
20 ├"'"
21 AVIEW
22 STOP
23 100
24 ÷
25 RCL 00
26 X<>Y
27 HMS-
28 "TRUE ALT:"
29 ARCL ST X
30 AVIEW
31 .END.
Example
Input: h_0: 35' (35 arcminutes, enter as 0.35)
Output:
REF: 27.9342' (27.9342 arcminutes) (R/S)
TRUE ALT: 0.0667 (6.67 arcminutes)
Source:
Meeus, Jean. Astronomical Algorithms. Willams-Bell Inc: Richard, VA 1991 ISBN 0-943396-35-2
Eddie
All original content copyright, © 2011-2020. Edward Shore. Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited. This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author.
Introduction
The program ATREF calculates the atmospheric refraction and the true "airless" altitude of a light from a star or any atmospheric object due to the Earth's atmosphere. As a result, the true altitude is generally lower than the apparent altitude.
Jean Meeus' "Astronomical Algorithms" (see source below) presents an approximation of calculating refraction by G.G. Bennett (University of New South Wales):
R = 1/(tan h_0 + 7.31/(h_0 + 4.4))
where:
R = atmospheric refraction, in arc minutes
h_0 = apparent altitude (the altitude you see), in hours-degrees-seconds format (HH.MMSSSS)
True altitude, in hours-degrees-seconds format (HH.MMSSSS) is calculated as:
h = R - h_0
HP 42S/DM42/Free 42 Program ATREF
00 { 74-Byte Prgm }
01▸LBL "ATREF"
02 DEG
03 "APP ALT?"
04 PROMPT
05 STO 00
06 →HR
07 ENTER
08 ENTER
09 4.4
10 +
11 1/X
12 7.31
13 ×
14 +
15 TAN
16 1/X
17 STO 01
18 "REF: "
19 ARCL ST X
20 ├"'"
21 AVIEW
22 STOP
23 100
24 ÷
25 RCL 00
26 X<>Y
27 HMS-
28 "TRUE ALT:"
29 ARCL ST X
30 AVIEW
31 .END.
Example
Input: h_0: 35' (35 arcminutes, enter as 0.35)
Output:
REF: 27.9342' (27.9342 arcminutes) (R/S)
TRUE ALT: 0.0667 (6.67 arcminutes)
Source:
Meeus, Jean. Astronomical Algorithms. Willams-Bell Inc: Richard, VA 1991 ISBN 0-943396-35-2
Eddie
All original content copyright, © 2011-2020. Edward Shore. Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited. This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author.
