http://www.perlmonks.org?node_id=1197907

Wearing a different hat I do the odd spot of astronomy observation. One of the observation areas I'm interested in is recording data for microlensing events which can be used for discovering exoplanets. Detected candidate events are published in various places around the internet, but a chunk of digging and analysis is required to find events that are interesting to observe "tonight". The following code scrapes one of the sites and uses heuristics involving the brightness of the event and various other parameters to choose and prioritize interesting current events from the thousand or so listed.

use strict; use warnings; use File::Copy; use HTML::Tree; use Astro::Time qw(); my $nowJD = Astro::Time::mjd2jd(Astro::Time::now2mjd()); my $root = HTML::TreeBuilder->new_from_url( 'http://ogle.astrouw.edu.pl/ogle4/ews/ews.html'); my @elements = $root->guts(); my @tables = $root->find('table'); my @rows = $tables[-1]->find('tr'); my @events; for my $row (@rows) { my @cells = $row->find('td'); my $flag = shift @cells; my ( $event, $field, $starNo, $ra, $dec, $tmaxHJD, $tmaxUT, $tau, $Umin, $Amax, $Dmag, $fbl, $ibl, $i0 ) = map {$_->as_text()} @cells; next if !$event || !$flag->find('img') || $Amax < 20; my $delta = abs($nowJD - $tmaxHJD); my $minMag = $i0 - $Dmag; next if $tau > 300 || $delta > $tau || $minMag > 16; $delta ||= 0.0001; $Umin ||= 0.0001; my $tRoot = $delta / $tau; my $uNow = sqrt($Umin * $Umin + $tRoot * $tRoot); my $aNow = ($uNow * $uNow + 2) / ($uNow * sqrt($uNow * $uNow + 4)) +; my $magNow = $i0 - 5 * log($aNow) / log(100); next if $magNow > 17; $magNow = sprintf "%.4f", $magNow; push @events, [$event, $tmaxUT, $tRoot, $tau, $ra, $dec, $Dmag, $m +agNow, $i0]; } for my $eventData (sort {$a->[2] <=> $b->[2]} @events) { my ($event, $tmaxUT, $tRoot, $tau, $ra, $dec, $Dmag, $magNow, $i0) + = map {s/^\s+|\s+$//g; $_} @$eventData; my $minMag = sprintf "%.3f", $i0 - $Dmag; print <<EVENT; $event: peak at $tmaxUT (tau $tau) RA $ra Dec $dec Mag $i0 - $minMag ( +now $magNow) EVENT }

Run at 6:29 UT 2017/08/24 printed:

2017-BLG-1600: peak at 2017-08-25.34 (tau 9.350) RA 17:43:38.19 Dec -2 +6:54:38.8 Mag 16.982 - 6.688 (now 14.6269) 2017-BLG-0019: peak at 2017-06-22.58 (tau 134.989) RA 17:52:18.74 Dec +-33:00:04.0 Mag 14.798 - 11.277 (now 13.8859)
Premature optimization is the root of all job security