Earth’s Moon has a diameter of 3,474 km and orbits at an average distance of 384,000 km. At that distance it subtends and angle just slightly larger than half a degree in Earth’s sky. Pluto’s moon Charon has a diameter of 1,186 km and orbits at a distance of 19,600 km from the dwarf planet. Compare the appearance of Charon in Pluto’s skies with the Moon in Earth’s skies. Describe where in the sky Charon would appear as seen from various locations on Pluto.

The reason for arriving at the above solutions is as follows:

The given dimensions and distance from the Earth of the Moon are;

The diameter of the Moon, d = 3,474 km

The average distance of the Moon from the Earth, R = 384,000 km

Required:

The comparison between Charon's appearance in Pluto and the Moon's appearance on Earth Earth

Solution:

The distance of the Moon's travels in an orbit, C = 2·π·R

∴ C = 2 × π × 384,000 km

The angle subtended by the Moon, θ = d/C × 360°

∴ θ = 3,474/(2 × π × 384,000) × 360° ≈ 0.518°

Pluto's moon Charon, has the following parameters;

The diameter of the Charon, d₂ = 1,186 km

The average distance of the Charon from Pluto, R₂ = 19,600 km

Therefore, the distance of the Moon's travels in an orbit, C₂ = 2·π·R₂

∴ C₂ = 2 × π × 19,600 km

The angle subtended by the Moon, θ₂ = d₂/C₂ × 360°

∴ θ₂ = 1,186/(2 × π × 19,900) × 360° ≈ 3.415°

The angle subtended by Charon in Pluto's sky ≈ 3.415°

Required:

The appearance of Charon as seen from different locations on Pluto

Solution:  

Charon is gravitationally locked to Pluto, therefore, the same side of Pluto is faced with the same side of Charon

Therefore;

Learn more about Pluto's moon Charon here:

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