06-12-2017, 12:15 PM
Given the right ascension (α) and declination (δ) of two stars of the same epoch (J2000.0 is the most current), the distance between the stars are:
d = acos( sin δ1 * sin δ2 + cos δ1 * cos δ2 * cos (α1 – α2) )
The distance is usually given in decimal degrees.
Enter α in terms of hours, minutes, seconds (standard notation) and δ in terms of degrees, minutes, seconds (standard notation).
HP Prime Program: ANGSTAR
Example
Distance between Regulus (A) in Leo and Sadalmelik in Aquarius:
(data via Wikipedia)
Regulus: α = 10h8m23.11s, δ = +11°58’01.95”
Sadamelik: α = 22h5m47.03593s, δ = -0°19’11.4568”
Distance: 168°20’05.1793”
Source:
Meeus, Jean. Astronomical Algorithms William-Bell, Inc. Richmond, VA 1991. ISBN 0-943396-35-2
d = acos( sin δ1 * sin δ2 + cos δ1 * cos δ2 * cos (α1 – α2) )
The distance is usually given in decimal degrees.
Enter α in terms of hours, minutes, seconds (standard notation) and δ in terms of degrees, minutes, seconds (standard notation).
HP Prime Program: ANGSTAR
Code:
EXPORT ANGSTAR(α1,δ1,α2,δ2)
BEGIN
// 2017-06-08 EWS
// Angular Angle
// Degrees
HAngle:=1;
LOCAL d;
α1:=15*α1;
α2:=15*α2;
d:=ACOS(SIN(δ1)*SIN(δ2)+
COS(δ1)*COS(δ2)*COS(α1-α2));
RETURN →HMS(d);
END;Example
Distance between Regulus (A) in Leo and Sadalmelik in Aquarius:
(data via Wikipedia)
Regulus: α = 10h8m23.11s, δ = +11°58’01.95”
Sadamelik: α = 22h5m47.03593s, δ = -0°19’11.4568”
Distance: 168°20’05.1793”
Source:
Meeus, Jean. Astronomical Algorithms William-Bell, Inc. Richmond, VA 1991. ISBN 0-943396-35-2