Whenever it is at its perigee, i.e. its closest distance to Earth. This happens every 27,55 days, a time interval known as an Anomalistic Month. The moon perigee can vary between 356000km and 370000km, so the moon's apparent size varies accordingly. However, you'd not be able to tell the difference without an accurate measurement.
The biggest moon is "Ganymede" which is a moon of Jupiter.
Phobos is the biggest moon of Mars.
Jupiters biggest moon is Ganymede
the biggest moon is gaymede
Titan is the biggest moon of saturn and the second biggest in the solar system
Ganymede is the biggest moon and orbits jupiter.
sun moon and earthBetween the Sun, Moon and the Earth, the Sun is the biggest.
The fourth biggest moon in our Solar System is Io a moon of Jupiter. See related question.
The moon does not change in size
Io is not. It's Ganymede, the biggest moon in the solar system.
venus has no moon
Ganymede(Jupiter) is the biggest moon and Titan (Saturn) is the 2nd biggest moon.