A recent series of images published by NASA on September 12th, 2019, captured a solar eclipse on Jupiter as its moon, Io, casts a shadow on the enormous planet’s north equatorial belt.
For those curious as to why the moon’s shadow on Earth during an eclipse appears fuzzy while Io’s shadow is so sharp, astrophysicist Dr. Katherine Mack explains:
Io is so big & close that it more than blocks the Sun (it appears 4x as big as the Sun from Jupiter’s perspective) and it’s so close that the penumbra (fuzzy outer edge of shadow) is super thin. [source]
NASA MSL ECAM team lead, Doug Ellison, also adds that the ‘sun is significantly smaller as seen from Jupiter – hence shadows are much sharper.’