Halley's Comet

It doesn't really make much sense to say that Halley's Comet visits planet Earth.

Like all comets (at least the ones we know about), Halley's Comet orbits the Sun, but on a highly eccentric path. When it gets close to the Sun it can be observed from Earth, but how close it gets to us depends on where the Earth is, at the appropriate time, in its orbit around the Sun.

The comet's perihelion (the closest it gets to the Sun) is about 0.6 astronomical units (AU), or just over half the distance at which the Earth orbits the Sun – somewhere between the orbits of Mercury and Venus. Its furthest distance from the Sun is outside the orbit of Neptune – close to that of Pluto (35 AU).

The comet's orbital period (which was what the question was really asking) varies, due to the gravitational influence of the planets, between 74 and 79 years. The time between the two most recent perihelions was 75 years and 295 days, or approximately 75.81 years (20 April 1910 to 9 February 1986).

The comet's 1986 appearance (or 'aparition') was the least favourable on record, observation being particularly difficult from the northern hemisphere. Wikipedia puts this down to "the comet and Earth [being] on opposite sides of the Sun in February 1986", but I'm not sure what this means; the two bodies must have been on the same side of the Sun either at the comet's perihelion or when it passed through our orbit.

In the name of the comet, 'Halley' is generally pronounced to rhyme with 'valley' (with 'Hailey' being the next most common, particularly in America). Wikipedia states that "Spellings of Edmond Halley's name during his lifetime included Hailey, Haley, Hayley, Halley, Hawley, and Hawly, so its contemporary pronunciation is uncertain." It seems to me that rhyming with valley is the least likely of the three possibilities to be correct; the most likely is Hawley, since Halley could be pronounced this way (as in Smalley).