Moon Illumination Issue

[jindal12ketan]

Here in function for Moon Illumination there should be some changes to be happen: 1) inc = atan(sdist * sin(phi), m['dist'] - sdist * cos(phi)), # comma should not be there after calculating atan 2) sdist = 149597870.7 position of sun should not be constant for given date

to calculate the distance between sun and earth we should use true_anomaly of sun like below.

`def true_anomaly(days): M = solar_mean_anomaly(days) E = M epsilon = 1e-6 maxiterations = 100 for in range(max_iterations): E_new = E - (E - e np.sin(E) - M) / (1 - e np.cos(E)) if abs(E_new - E) < epsilon: break E = E_new

theta = 2 * np.arctan(np.sqrt((1 + e) / (1 - e)) * np.tan(E / 2))
return theta`

[kylebarron]

Is this closed by https://github.com/kylebarron/suncalc-py/pull/18 now?

[jindal12ketan]

`def getMoonIllumination(date):

d = to_days(date)
s = sun_coords(d)
m = moon_coords(d)

# distance from Earth to Sun in km
sdist = 149598000

phi = acos(
    sin(s['dec']) * sin(m['dec']) +
    cos(s['dec']) * cos(m['dec']) * cos(s['ra'] - m['ra']))
inc = atan(sdist * sin(phi), m['dist'] - sdist * cos(phi))
angle = atan(
    cos(s['dec']) * sin(s['ra'] - m['ra']),
    sin(s['dec']) * cos(m['dec']) -
    cos(s['dec']) * sin(m['dec']) * cos(s['ra'] - m['ra']))

return {
    'fraction': (1 + cos(inc)) / 2,
    'phase': 0.5 + 0.5 * inc * np.sign(angle) / PI,
    'angle': angle}

`

Why do we keep the distance of the sun-earth constant? Isn't the distance between Earth and the sun by date and time?

[kylebarron]

This library is a direct port of the upstream https://github.com/mourner/suncalc. It's been a while since I've worked with the code, so you'd have to look at the upstream version and ask questions there.

[jindal12ketan]

Okay