User guide to program with guitastro Python classes

This section show how to use guitastro in a Python code.

1. Context

Celestial mechanics allow to compute celestial bodies positions and manage dates, durations, angles, coordinates

2. Python classes provided by guitastro

Brief descrition of the guitastro classes:

• Angle: Convert angles in complex formats.
• Coords: Convert angles in complex formats.
• Home: Define a mount location on the Earth surface.
• Horizon: Define horizon line to set the limits of telescope pointings.
• Atmosphere: Define atmospheric conditions to set the conditions to compute refraction effects.
• Site: Define an observation site by merging Home, Horizon, Atmosphere.
• Date: Convert dates in complex formats.
• Duration: Convert durations in complex formats.
• Mechanics: Low level methods for celestial mechanics
• Targets: High level methods for celestial mechanics

3. Using the Python module guitastro for angles

3.1. Simple example to convert angles

import guitastro
a = guitastro.Angle("2h3m27s")
print("angle deg =", a.deg())

angle deg = 30.862499999999994

3.2. Operation with angles

We want to compute sum of the angles 2h3m27s and -0d28m12.4s. Display the results in sexagesimal format expressed in degrees:

import guitastro
a = guitastro.Angle("2h3m27s")
b = guitastro.Angle("-0d28m12.4s")
c = a + b
print("{}".format(c.sexagesimal("d")))

'30d23m32.60s'

4. Using the Python module guitastro for dates

Celme module is located in the folder pyros/src/utils Examples: pyros/src/utils/report/dates.py help(Date)

4.1. Simple example to convert dates

import guitastro
a = guitastro.Date("now")
print("Date ISO =", a.iso())
Date ISO = 2018-10-11T22:45:44.958
print("Date Julian Day =", a.jd())

Date Julian Day = 2458403.448437011

4.2. Operation with dates

We want to compute date corresponding to add 2 days and 28 minutes to the 2018-10-11T22:45:44.958. Display the results in ISO format:

import guitastro
a = guitastro.Date("2018-10-11T22:45:44.958")
b = guitastro.Duration("2d28m")
c = a + b
print("Date ISO =", c.iso())

Date ISO = 2018-10-13T23:13:44.958

5. Using the Python module guitastro for ephemeris

help(Target)

5.1. Simple example to compute Sun coordinates

First we compute RA, DEC coordinates of the Sun:

import guitastro
date = guitastro.Date("now")
site = guitastro.Site("GPS 0 E 49 200")
skyobj= {'planet':'Sun'}
target = guitastro.Target()
target.define(skyobj)
output0s = ['ra','dec']
results = target.ephem(date,site,output0s)
ra = results['RA']
dec = results['DEC']

Second, we inject RA, DEC to compute its local coordinates:

skyobj= {'RA':ra , 'DEC':dec }
outputs = ['elev']
target.define(skyobj)
results = target.ephem(date,site,outputs)
elev = results['ELEV']

6. Angle formats

Input accepted formats:

Sexagesimal formating using uspzad convention rad is an angle in radian Sexagesimal format:

• u (unit) = h,H,d,D (default=D). Capital mean module [0:360[, lower case means module [-180:180[
• s (separator) = " ",:,"" (default="" means letters hms or dms)
• p (plus/minus) = +,"" (default="")
• z (zeros) = 0,"" (default="")
• a (angle_limits) = "",90, (+/-limit if unit D,H, default="" means 360)
• d (sec_digits) = "",".1",".2",... (default="")

Style 1:

• To Display a R.A.: "H0.2" => 23h07m42.49s
• To Display a Decl.: "d+090.1" => +00d34m22.6s
• To Display a H.A.: "h0.2" => -08h43m16.05s

Style 2:

• To Display a R.A.: "H 0.2" => 23 07 42.49
• To Display a Decl.: "d +090.1" => -00 34 22.6
• To Display a H.A.: "h 0.2" => -08 43 16.05

Style 3:

• To Display a R.A.: "H:0.2" => 23:07:42.49
• To Display a Decl.: "d:+090.1" => -00:34:22.6
• To Display a H.A.: "h:0.2" => -08:43:16.05

7. Date formats

Input accepted formats:

• now = Now. e.g. "now"
• jd = Julian day. e.g. 24504527.45678
• iso = ISO 8601. e.g. 2018-02-28T12:34:55.23
• sql = ISO 8601. e.g. 2018-02-28 12:34:55.23
• ymdhms = Calendar. e.g. 2018 2 28 12 34 55.23
• equinox = Equinox. e.g. J2000,0
• digits = Pure digits e.g. 20180228123455.23