Apparent diameter plot for Jupiter 2017-2026

The apparent diameter of Jupiter varies with the Earth-Jupiter distance. Depending on the distance, the apparent angular diameter of Jupiter is between approx. 0.5 and 0.8 arcminutes. For best astrophotography results, one should pick a time when Jupiter is closest. Similar to my plot of the apparent size of Venus, I wrote a short program to plot Jupiter’s apparent diameter for the time period 2017-2026 (see featured image).

Apparent diameter plot for the Moon 2017-2018

The apparent diameter of the Moon varies with the Earth-Moon distance. Depending on the distance, the apparent angular diameter of the Moon is between 29.4 and 33.5 arcminutes. For best astrophotography results, one should pick a time when the moon is closest. Similar to my plot of the apparent size of Venus, I wrote a short program to plot the Moon’s apparent diameter (see featured image).

Venus apparent diameter plot for 2017-2020

The apparent size of Venus varies dramatically with the Earth-Venus distance, depending on both orbits around the sun. The apparent angular diameter of Venus is between 0.175 and 1 arcminutes.

Wikipedia has nice images on that and says that…

“the extreme crescent phase of Venus can be seen without a telescope by those with exceptionally acute eyesight, at the limit of human perception.”

I will definitely try next time with my naked eyes, but if you have an entry-level telescope, you will be certainly be better able to see the crescent phase during closest approach.

The question is, when does Venus come closest to Earth for best observation? Not finding anything on the interwebs, I wrote a quick plotting program with Python’s ephem package and gnuplot.

Venus apparent diameter plot for 2017-2020

Graph of apparent diameter of Venus in arcminutes for the time period 2017-2020
Graph of apparent diameter of Venus in arcminutes for the time period 2017-2020

Here is the very short Python program that calculates the apparent diameter of Venus for 4 years beginning with January 2017:

#!/usr/bin/python3

import datetime as dt
import ephem
import math
from math import radians as rad, degrees as deg

venus = ephem.Venus()

venus_diameter_meters = 2 * 6051800
au_meters = 149597870700

t = dt.datetime.strptime("20170101", "%Y%m%d")

diff = dt.timedelta(days = 1)

for i in range(0, int(4 * 365)):
    venus.compute(t)
    
    dist_venus_meters = venus.earth_distance * au_meters
    
    angular_diameter_arcminutes = 60 * deg(2 * math.asin(venus_diameter_meters / (2 * dist_venus_meters)))
    
    print(t.strftime("%Y-%m-%d"), angular_diameter_arcminutes)
    t += diff