The new house is three stories, and gets lots of natural light. Sadly, none of its third story windows is well-placed for stargazing. If one was, I'd have more time to look through my telescope and more inspiration to write silly astronomy code. Maybe when we overhaul the third floor, we'll put in a window on the slant of the roof. Probably not.
Since I don't do much stargazing, my last need for astronomical Perl code came while working on the RPG that I run. It's space-based, and I wanted to get an idea of distance between various star systems. There were a number of Astro modules on the CPAN, but most of them either lacked the few features I needed or required third party libraries that didn't just work out of the box.
Since I didn't need much at all, I just broke out my copy of Practical Astronomy For Your Personal Computer (a fantastic book that I've never regretted buying), and wrote this silly little program. It would be a lot more fun if there was a giant and easy to access database of stars. I think I'll need to dig more for that.
package Astro;
use Math::Trig ();
use strict;
use warnings;
# Stars are located by their RA (right ascension), declination, and distance
# from earth.
# RA is usually expressed in hms: hours, minutes, seconds
# dec is usually expressed in dms: degrees, arcminutes, arcseconds
# distance is usually expressed in light years
# Spherical coordinates are usually expressed as [ rho, phi, theta ]
# rho - distance from center
# phi - one angle, in degrees
# theta - one angle, in degrees
# A star's position can be expressed as [ dist, dec, ra ]
sub hms_to_dms {
my ($hours, $minutes, $seconds) = @_;
return map { $_ * 15 } @_;
}
sub dms_to_d {
my ($deg, $arcmin, $arcsec) = @_;
return $deg + $arcmin/60 + $arcsec/3600;
}
# given RA in hms, dec in dms, distance in ly
sub star_to_xyz {
my ($dist, $dec, $ra) = @_;
my $dec_deg = dms_to_d(@$dec);
my $ra_deg = dms_to_d(hms_to_dms(@$ra));
for my $deg ($dec_deg, $ra_deg) {
$deg = 360 - $deg if $deg < 0;
}
my $dec_rad = Math::Trig::deg2rad($dec_deg);
my $ra_rad = Math::Trig::deg2rad($dec_deg);
return my ($x, $y, $z)
= Math::Trig::spherical_to_cartesian($dist, $dec_rad, $ra_rad);
}
sub dist {
my ($p1, $p2) = @_;
my $mhd
= ($p2->[0] - $p1->[0]) ** 2
+ ($p2->[1] - $p1->[1]) ** 2
+ ($p2->[2] - $p1->[2]) ** 2;
return $mhd ** 0.5;
}
sub star_dist {
my ($star1, $star2) = @_;
my @s1_xyz = star_to_xyz(@$star1);
my @s2_xyz = star_to_xyz(@$star2);
print "star1: @s1_xyz\n";
print "star2: @s2_xyz\n";
dist(\@s1_xyz, \@s2_xyz);
}
my @aca = star_to_xyz( 4.36, [ -60, 50, 2 ], [ 14, 39, 37 ]);
my @acb = star_to_xyz( 4.36, [ -60, 50, 14 ], [ 14, 39, 35 ]);
my @wolf = star_to_xyz( 7.78, [ 7, 00, 42 ], [ 10, 56, 37 ]);
my %star = ( # dist, dec, ra
capella => [ 42.20, [ 45, 59, 53 ], [ 5, 16, 41 ] ], # Alpha Aurigae
castor => [ 49.77, [ 31, 53, 18 ], [ 7, 34, 36 ] ], # Castor
centauri => [ 4.36, [ -60, -50, -2 ], [ 14, 39, 37 ] ], # a; Rigil Kent
# toliman, bungula
draconis => [ 18.78, [ 69, 39, 40 ], [ 19, 32, 21 ] ], # Sigma Draconis
eridani => [ 10.52, [ - 9, -27, -30 ], [ 3, 32, 56 ] ], # Epsilon Eridani
errai => [ 45.00, [ 77, 37, 56 ], [ 23, 39, 21 ] ], # Gamma Cephei
geminorum => [ 33.72, [ 28, 1, 35 ], [ 7, 45, 19 ] ], # Pollux
gliese => [ 51.81, [ 29, 53, 48 ], [ 20, 3, 37 ] ], # Gliese 777; bin
luyten => [ 8.72, [ 17, 57, 0 ], [ 1, 39, 1 ] ], # 726-8
mensae => [ 33.10, [ -74, -45, -11 ], [ 6, 10, 14 ] ], # Alpha Mensae
pavonis => [ 30.10, [ - 5, -21, -58 ], [ 21, 26, 26 ] ], # gamma
pegasi => [ 53.00, [ 12, 11, 00 ], [ 22, 46, 42 ] ], # Xi Pegasi
persei => [ 34.40, [ 49, 36, 48 ], [ 3, 9, 4 ] ], # Iota Persei
reticuli => [ 39.51, [ -62, -34, -31 ], [ 3, 17, 42 ] ], # Zeta (binary)
scorpii => [ 45.70, [ - 8, -22, - 6 ], [ 16, 15, 37 ] ], # 18 Scorpii
sol => [ 0.00, [ 0, 0, 0 ], [ 0, 0, 0 ] ], # YOU ARE HERE
tau_ceti => [ 11.89, [ -15, -56, -14 ], [ 1, 44, 4 ] ], # Tau Ceti
tucanae => [ 28.00, [ -64, -52, -29 ], [ 0, 20, 4 ] ], # Zeta
wolf => [ 7.78, [ 7, 00, 42 ], [ 10, 56, 37 ] ], # Wolf 359
zavijava => [ 35.60, [ 1, 45, 53 ], [ 11, 50, 42 ] ], # Beta Virginis
);
if (@ARGV == 2) {
print star_dist($star{$ARGV[0]}, $star{$ARGV[1]}), "\n";
} else {
my @max = (0, undef, undef);
for my $star1 (keys %star) {
next unless $star{$star1};
for my $star2 (grep { $_ ne $star1 } keys %star) {
next unless $star{$star2};
my $dist = star_dist($star{$star1}, $star{$star2});
@max = ($dist, $star1, $star2) if $dist > $max[0];
}
}
print "@max\n";
}
1;
Are you thinking about something like the New General Catalogue (NGC)? Or one of the specialised star catalogues?
PS.: <ecode> tags automatically escape their content, so if you escape it as well it comes out with gibberish.
Re:Database of stars
rjbs on 2006-10-13T13:01:52
The NGC or any full-sky catalog would be swell.
As for ecode, I really thought I'd fixed my posting script... hmph!Re:Database of stars
Aristotle on 2006-10-13T14:03:43
Something like The Interactive NGC Catalog Online?
Re:Database of stars
rjbs on 2006-10-20T13:24:04
Beyond the fact that the form doesn't seem to work properly in Firefox, this lacks information like "distance," and doesn't seem to have any system for better machine queries.
The HYG database looks potentially like just what I wanted. Now, to make an interface...