For backyard astronomers, this week will be a great time to get outside and look up, not only because the Perseid meteors, which peaked on Sunday, will still be visible until August 22nd, but also because Venus and Mercury will both reach elongation, or their greatest angular distance from the Sun.
Elongation is the best time to view these two inferior planets. No, I’m not engaging in name-calling; to call a planet inferior simply means that it orbits closet to the sun than the Earth, as both Venus and Mercury do.
“Elongation” is one of a handful of terms astronomers use to describe a planet’s position in relation to the Sun and the Earth. It means that the other planet is at it’s farthest angle from the Sun, as viewed from Earth.
Other terms include “superior conjunction,” when a planet passes behind the Sun (making it impossible to see), as viewed from the Earth, “inferior conjunction,” when an inferior planet passes near the front of the Sun, as viewed from Earth (also making it impossible to see), and “opposition,” when a superior planet (one whose orbit is beyond our own) is on the exact opposite side of the Earth from the Sun.
Opposition is the best time to view a superior planet, because it is visible for more of the night than at any other time. For an inferior planet, though, elongation is the best time to watch, because there is no conjunction.
Venus reached its greatest brilliancy for the year in mid-July, but it remains a bright fixture in the morning sky. Mercury will be joining it, as well as Jupiter, each morning for it’s best show December.