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Eclipses in the Solar System
Author: Bill Kramer
Last update: July 18 2017

Solar System Moons Angular Size Table

-by Bill Kramer

Click here for the related Study - Do other planets see solar eclipses?


Moons tested

Planet name Radius (KM) Moons Distance to Sun
(KM)
Angular Size
(Degrees)
Earth63711150,000,0000.53147
Mars33902228,000,0000.34965
Jupiter6991150778,000,0000.10247
Saturn58232531,427,000,0000.05587
Uranus25362272,870,000,0000.02778
Neptune2462284,497,000,0000.01773

Comparing the angular sizes

Using data from the NASA Planetary Fact Sheets about the moons, the following table shows the angular size of the moon at the extremes of the orbit. The angular sizes are compared to the angular size of the Sun. The comparison is accomplished in terms of a ratio. Angular sizes of the moon are divided into the angular size of the Sun. If the ratio is greater than 1.0 then an annular eclipse event can take place. For ratios less than one, a total eclipse event can take place.

Math Details

For these results, the distance to the moon was supplied as seen from the center of the host planet. This value was used to simulate viewing from the poles and modified by the mean radius of the host planet to simulate observations at the equator. Each entry has four values for the angular sizes as seen from the host planet. The first two are from the perspective of an observer at the equator. The last two are for an observer at the poles. The two values for each are that for when the moon is closest (periapsis) and farthest (apoapsis).

Columns in table

Planet is the name of the planet. Other than Earth, all the planets have multiple moons. Moon is the name of the moon in orbit about the planet. Size is the size of the moon's radius in kilometers. Distance is the number of kilometers from the surface (or cloud tops) of the planet to the moon and has four values. The top value is the distance from the surface of the planet at the equator to the moon when the moon is closest. The second value is the distance from the surface of the planet at the equator to the moon when the moon is farthest. The third and fourth distances are from the center of the planet which is the same distance as would be seen from the poles for periapsis and apoapsis.Angular Size (moon) corresponds to the distance and is the apparent size of the moon as seen from the surface of the planet at the equator (top two values) and the poles (lower two values). Angular size is measured in degrees. Angular Size (Sun) is the apparent size of the Sun as seen from the planet measured in degrees. Ratio Sun/moon is the value of the the angular size of the Sun divided by the angular size of the moon. A value greater than one indicates the conditions for an annular eclipse. A value less than one indicates the conditions for a total solar eclipse. The top value is the ratio when the moon is closest to the surface of the planet at the equator. The second ratio when the moon is farthest from the surface of the planet at the equator. The third and fourth values are where the moon is closests (periapsis) and fartherst (apoapsis) from the poles.Ratio moon/Sun is the value of the inverse of the corresponding Sun/moon ratio. In this case a value greater than one indicates a total eclipse of the Sun and a value less than one is an annular type eclipse of the Sun as viewed from the surface of the planet.

The program is searching for where the ratios bridge the value of one. That is if any value is greater than one and another is less than one. Under those conditions, a total and annular eclipse are possible and this would be the most Earth-like.


= = = > Jump to summary

Planet Moon Size (radius KM) Distance (KM)
Periapsis/Apoapsis
Angular Size (moon)
Periapsis/Apoapsis
Angular Size (Sun) Ratio Sun/moon Ratio moon/Sun
EarthMoon1,737.1356,924
399,132
363,295
405,503
0.557696
0.498722
0.547916
0.490887
0.5314720.953
1.066
0.970
1.083
1.049
0.938
1.031
0.924
JupiterCallisto2,408.41,799,610
1,825,968
1,869,521
1,895,879
0.153357
0.151143
0.147622
0.145570
0.1024700.668
0.678
0.694
0.704
1.497
1.475
1.441
1.421
SaturnJanus90.492,180
94,300
150,412
152,532
0.112379
0.109852
0.068871
0.067914
0.0558660.497
0.509
0.811
0.823
2.012
1.966
1.233
1.216
SaturnEpimetheus58.391,827
94,553
150,059
152,785
0.072753
0.070656
0.044520
0.043726
0.0558660.768
0.791
1.255
1.278
1.302
1.265
0.797
0.783
SaturnPandora40.682,873
84,063
141,105
142,295
0.056139
0.055344
0.032971
0.032696
0.0558660.995
1.009
1.694
1.709
1.005
0.991
0.590
0.585

^^^ Jump to top of table

Summary data

Found Earth-like eclipse conditions for: Earth/Moon, Saturn/Epimetheus, Saturn/Pandora
Moons investigated: 141
Maximum Solar/Moon ratio: 27,558.7
Minimum Solar/Moon ratio: 0.037737
Total eclipses: 32 - where the Sun is completely covered at both apoapsis and periapsis.
Annular eclipses: 107 - where Sun is visible around occulting moon at both apoapsis and periapsis.
Extreme totals (moon over 2x size of Sun): 30
Extreme annulars (Sun over 2x size of moon): 105
Number of very interesting eclipses, where moon appears less than twice the size of the Sun allowing a view of the corona, is 5 with 3 making a near perfect fit (one to one) - annular at apoapsis, total at periapsis.
Of the moons in the solar system, 22.7% were total only, 75.9% were annular only and 3.5% are ideal.

Click here for the related Study - Do other planets see solar eclipses?



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