Solar system objects and polar plots¶

In this seminar, we will try to obtain the coordinates for several solar system objects and plot them in polar coordinates.

Sources¶

import numpy as np
from matplotlib import pylab as plt

from mpl_toolkits.basemap import Basemap

import ephem

First, we set the observer coordinates and time. The simplest way to set the time in ephem, is to use Greenwich mean time.

NHAO     = ephem.Observer()
NHAO.lon = "134.3356"
NHAO.lat = "35.025"
NHAO.date= "2019/06/26 7:00"

Local coordinates of the sun¶

SUN = ephem.Sun()
SUN.compute(NHAO)

print("Declination:     ", float(SUN.dec)/np.pi*180.)     ## (赤緯)
print("Right ascension: ", float(SUN.ra)/np.pi*180.) ## (赤経)

print("Elevation        ", float(SUN.alt)/np.pi*180.)
print("Azimuth:         ", float(SUN.az)/np.pi*180.)

('Declination:     ', 23.361049160609934)
('Right ascension: ', 94.80873881042564)
('Elevation        ', 38.24565450277015)
('Azimuth:         ', 273.6895322691028)

Local coordinates of Planets, Sun and Moon¶

ephem._libastro.builtin_planets()

[(0, 'Planet', 'Mercury'),
 (1, 'Planet', 'Venus'),
 (2, 'Planet', 'Mars'),
 (3, 'Planet', 'Jupiter'),
 (4, 'Planet', 'Saturn'),
 (5, 'Planet', 'Uranus'),
 (6, 'Planet', 'Neptune'),
 (7, 'Planet', 'Pluto'),
 (8, 'Planet', 'Sun'),
 (9, 'Planet', 'Moon'),
 (10, 'PlanetMoon', 'Phobos'),
 (11, 'PlanetMoon', 'Deimos'),
 (12, 'PlanetMoon', 'Io'),
 (13, 'PlanetMoon', 'Europa'),
 (14, 'PlanetMoon', 'Ganymede'),
 (15, 'PlanetMoon', 'Callisto'),
 (16, 'PlanetMoon', 'Mimas'),
 (17, 'PlanetMoon', 'Enceladus'),
 (18, 'PlanetMoon', 'Tethys'),
 (19, 'PlanetMoon', 'Dione'),
 (20, 'PlanetMoon', 'Rhea'),
 (21, 'PlanetMoon', 'Titan'),
 (22, 'PlanetMoon', 'Hyperion'),
 (23, 'PlanetMoon', 'Iapetus'),
 (24, 'PlanetMoon', 'Ariel'),
 (25, 'PlanetMoon', 'Umbriel'),
 (26, 'PlanetMoon', 'Titania'),
 (27, 'PlanetMoon', 'Oberon'),
 (28, 'PlanetMoon', 'Miranda')]

NAMES  = ephem._libastro.builtin_planets()[:10]
getattr(ephem, NAMES[0][2])

ephem.Mercury

TEN_CO = []
for i in NAMES:
    OBJ = getattr(ephem, i[2])()
    OBJ.compute(NHAO)
    
    ALT = float(OBJ.alt)/np.pi*180.
    AZ  = float(OBJ.az)/np.pi*180.
    
    TEN_CO.append([AZ,ALT])

Let`s print the computed horizontal coordinates (Az, Alt).

TEN_CO

[[250.86760262928578, 58.44127053878516],
 [280.51163449513825, 26.147900501438507],
 [256.23689629810286, 56.993239698891195],
 [101.95890559017263, -22.894633588437244],
 [82.94807807325012, -49.668971719792644],
 [298.66753406383947, -15.564129646626476],
 [328.8854657445131, -56.65896682581618],
 [79.7982133940937, -53.38434874146946],
 [273.6895322691028, 38.24565450277015],
 [303.4361535762889, -37.83429952981697]]

NHAO.date.datetime()

datetime.datetime(2019, 6, 26, 6, 59, 59, 999999)

Let's plot the coordinates onto a cartesian map.

plt.figure(figsize = (12,9))

n = 0
for i in TEN_CO:
    plt.plot(i[0],i[1], "o")
    plt.text(i[0],i[1], NAMES[n][2])
    n+=1 ### n = n+1

plt.xlabel("Azimuth [deg]")
plt.ylabel("Elevation [deg]")
plt.grid(True)
plt.show()

Following, we will plot the data points onto a 2D projection of a 3D sphere. Therefore, we can define a Basemap object, which requires the projection.

def sphere_plot(COORDINATES, NAMELIST, lon_0 = 0, lat_0 = 90):

    plt.figure(figsize = (10,10))
    SPHERE = Basemap(projection='ortho',
                     lon_0=lon_0,
                     lat_0=lat_0)
    ### create meridians and geodesics 
    SPHERE.drawmeridians(np.arange(0.,420.,30.))
    SPHERE.drawparallels(np.arange(-90.,120.,15.))
    horizon = SPHERE.drawparallels([0], color = "r", linewidth=4)
    n = 0
    for i in COORDINATES:
        j0,j1 = SPHERE(i[0],i[1])
        plt.plot(j0,j1, "o")
        plt.text(j0,j1, NAMELIST[n][2])
        n+=1 ### n = n+1
    plt.show()
    
sphere_plot(TEN_CO,NAMES)

sphere_plot(TEN_CO,NAMES, -30,20)

Table of Contents

Solar system objects and polar plots¶

Sources¶

Local coordinates of the sun¶

Local coordinates of Planets, Sun and Moon¶