Astro

Robert Estalella

Astro (version 23.05)

Astro is a simple program with a graphical interface with the aim of showing, for a given location and time, the position; rising, setting and culmination times; distance, apparent size, phase; of the planets, Moon, Sun, bright stars and Messier objects. The Sun, Moon, and planets positions are calculated following Paul Schlyter's recipes (http://www.stjarnhimlen.se/comp/ppcomp.html). The program uses the Dislin widgets (https://www.dislin.de) for the graphical interface (see below).

Requisites

Linux system, Dislin library, gfortran compiler.

Installation

Download the tar file astro.tgz in the installation directory you like (for example $HOME/astro) and run:

$ tar -xzvf astro.tgz

$ astro_compile

Additionally, if you want to be able to run astro from any location in your computer, you have to define the environment variable ASTRO_DIR pointing to your installation directory. This can be done by adding to your .bashrc file the lines

#astro

export ASTRO_DIR=$HOME/astro

and making a symbolic link to astro from a directory in your path (for example $HOME/bin)

$ ln -s $HOME/astro/astro .

Usage

$ astro [-h|-l <lang>|-c <config_file>]

Options

-h: Shows a short message showing usage and options, and quits.

-l <lang>: Selection of language. <lang> can be one of eng, cat, esp, fr.

The keywords and labels used by astro are stored in text files astro_eng.txt, astro_cat.txt, . . . etc. The default language is set in the configuration file astro.conf, and is superseded by this option. Any new language <lang> can be easily added by copying astr_eng.txt to a new file astro_<lang>.txt and translating its content line by line.

-c <config_file>: Selection of an alternative configuration file instead of astro_conf.txt (see below).

Configuration

The configuration file astro_conf.txt contains 4 lines with the coordinates (latitude and longitude in degrees and fraction, elevation in m) of the default location, and the default language. As shipped, the file contains:

+41.3798 !Latitude N [deg] (Sant Just Desvern, Barcelona, Spain)

+02.0799 !Longitude E [deg]

120 !Elevation [m]

eng !Default language

Description

Table cells with white background in the Location, Epoch, and Sky Position tables can be changed with push buttons (see figure below), All values shown in the tables are updated whenever a change is made. by clicking a push button or selecting a sky object.

1st and 2nd columns

Location, Epoch, and Sky Position push buttons:

[Reset] or [Update]: reset default location, or zero RA and Dec, or update current epoch to that given by the system.
[Decrease | Increase]: select sign of step.
[0.1 | 1 | 10]: select step magnitude.

The rest of push buttons increase or decrease one step the value of latitude, longitude, elevation, date, time, time zone, RA, or Dec.

Sky Object list: select one of the following

Custom: the coordinates can be entered with the Sky Position push buttons.
Sun, Moon, and planets Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune: the coordinates are calculated for the current epoch and location.
Bright Stars: a star can be selected from the list of 95 stars brighter than mag 2.5.
Messier Objects: an object can be selected from the catalog of Messier objects.
Miscellaneous: Large and Small Magellanic Cloud, Galactic center, Aries point, etc.

3rd column

Location table:

Latitude N: [d:m:s], [deg and fraction], positive North.
Longitude E: [d:m:s], [deg and fraction], positive East of Greenwich.
Elevation:[m], above sea level.

Horizon dip: ['], horizon-dip angle caused by the elevation, in arcmin.
Horizon distance: [km], distance to the horizon.

Epoch table:

Local Date: [y-m-d], [year and fraction].
Local Time: [h:m:s], [hr and fraction].
Time Zone: [h:m], [hr and fraction]. Local time -UT.
Month: name of the month.

Day of Year: 1 to 365 or 366.
Day of Week: Monday, Tuesday, . . . etc

Universal Time table:

UT Date: [y-m-d], [year and fraction]. Can be a day before or after the local date.
UT Time: [h:m:s], [hr and fraction].

Sidereal Time table,:

Greenwich ST:[ h:m:s], [hr and fraction].
Local ST: [h:m:s], [hr and fraction]. RA of the local meridian.

Sky Position

Equatorial Coordinates table (apparent, geocentric, except for the Moon, which are topocentric):

Right Ascension: [h:m:s], [hr and fraction].
Declination: [d:m:s], [deg and fraction].
Hour Angle: [h:m:s], [hr and fraction] Angle from the local meridian.

Horizontal Coordinates table (apparent, geocentric, except for the Moon, which are topocentric):

Azimuth (N): [d:m:s], [deg and fraction], measured from North to East.
Altitude: [d:m:s], [deg and fraction].

4th column

Physical data table:

Distance: The topocentric distance is given in Earth radii [R_T] for the Moon, and the geocentric distance in astronomical units [au] for the Sun and planets, or parsecs [pc], [kpc], [Mpc] for stars, and galactic and extragalactic objects.
Angular size: The size is given in arcmin ['] for the Moon, Sun, and Messier objects, in arcsec [''] for the planets.
Brightness:[mag] Visual magnitude.
Solar elongation E: [deg] Angular distance from the Sun.
- Positive eastwards, lagging the Sun, visible after sunset.
- Negative westwards, leading the Sun, visible before sunrise.
- For the Moon, positive elongation is for a crescent moon (first half-cycle, between new and full moon), negative is for a waning moon (second half-cycle, between full and new moon).
Phase (illuminated fraction): Fraction of planet or Moon's disk illuminated by the Sun.

Visibility:

Rising & Setting: The sky objects rises, culminates, and sets along a day. The rising, setting, and upper meridian crossing are shown in the tables.
Circumpolar: The sky object remains visible all day, crossing twice the meridian. The upper and lower meridian crossings are shown in the tables.
Invisible: The sky object remains all day below the horizon.

Rising, and Setting tables:

Local Time: [h:m:s],[ hr and fraction].
UT Time: [h:m:s], [hr and fraction]. Time of the rising above or setting below the horizon of the upper limb (Sun and Moon) or center of the sky object. The refraction at the horizon and horizon-dip angle are taken into account.
Azimuth (N): [d:m:s], [deg and fraction]. Azimuth of the rising or setting.

Upper Meridian Crossing, and Lower Meridian Crossing tables:

Local Time: [h:m:s], [hr and fraction].
UT Time: [h:m:s], [hr and fraction]. Time of the meridian crossing of the center of the sky object.
Altitude: [d:m:s], [deg and fraction]. Altitude of the meridian crossing, coinciding with the upper or lower culminations (only approximately for the Sun and Moon).

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