Has your body ever suffered from inferior conjunction? Don't know? Well there is one body experiencing that phenomenon - today as a matter of fact. It is tiny Mercury. But what exactly is this condition, and do we have to worry about catching it?

Inferior conjunction is merely a term which tells one about the position of one body with respect to two others. Some readers may recognize the term "conjunction" from phrases like "The planets were aligned; they were in conjunction." It is a term derived from the Latin word meaning "connected," which is how two heavenly bodies look when they are lined up in the skies.

In today's event Mercury lines up with the Sun, passing in front of our star, or as close as it can. The two are in conjunction, but why the "inferior"?

Mercury and Venus, being on the inside lanes of our solar system race course, can actually line up with the Sun twice, once as they pass between us and the Sun, and once again on the far side as they pass behind our star.

The inside alignment is called inferior conjunction. That more distant alignment is called superior conjunction.

The outer planets (Mars, Jupiter, et al.) only get to be "in conjunction" with the sun - no inferior or superior is involved. They can only be aligned with the sun when on the far side of the sun; they never come between us and our star.

And when those outer planets happen to be on the opposite side of our planet when compared to the sun we get yet another term; those planets are then in "opposition."

You may be curious as to why little Mercury and Venus do not often actually pass directly in front of the sun when they are in inferior conjunction. (Mercury missed doing so today as a matter of fact.) It is for the same reason that the Moon, when it passes in front of the sun every month, does not always give us an eclipse.

The orbits of Mercury and Venus compared to our orbit are not perfectly lined up. Sometimes the planets pass just "below" the sun, at other times they pass "above." Occasionally they do pass right in front of the sun, appearing as tiny dots crawling across that brilliant face. That is called a "transit."

Had your fill of new astronomy terms? But I didn't even mention western or eastern quadrature, or greatest western or greatest eastern elongation. Or eclipse or occultation or the ever-amusing syzygy! Alas!

All right then. Maybe we can line them up for a future article. Until next time, clear skies!