Unless you’ve been living under a rock — and even if you have, there’s probably still some pretty decent Wi-Fi down there — you probably got bombarded by all the total solar eclipse madness last week. We didn’t make the road trip down to Oregon to experience totality nor did we get the special glasses in time, so we mostly lived vicariously through everyone else’s excitement.

And then I made the mistake of randomly scrolling through my Facebook feed, as I am apt to do, only to see that some people were confusing the term “eclipse” with two other words that look and sound somewhat similar: ellipse and ellipsis. While they were not referring to the cosmic phenomenon as a solar ellipse or a solar ellipsis, they were using the word “eclipse” when they really meant one of the others.

The word eclipse can be used both as a noun and as a verb. In the context of last week’s big event, it refers to when one celestial body (the moon) passes in front of another (the sun), thus obstructing the light from the latter from the point of view of the observer. With a lunar eclipse, the moon appears to go dark when the Earth blocks the sun’s light from hitting the moon.

We most commonly use this word in the context of astronomy, but it can be used to refer to obscuring any light. In more of a symbolic sense, it could mean to surpass or to diminish something else by comparison. If you were to say that the talent of the student eclipsed that of the teacher, it would mean the teacher’s talent is being drowned out by the student’s. The student has surpassed the teacher and thus the “light” of the teacher’s talent doesn’t shine as brightly.

Swap out just a single letter and you get the word ellipse. This has nothing to do with obscuring light or surpassing another. Instead, it’s a particular type of two-dimensional geometric shape. It’s an oval such that the sum of the distances from two fixed points (called the foci, plural of “focus”) stays constant.

Think of it this way. If you have a perfect circle, the distance from the exact center to any point along the circle will always be the same (the radius). With an ellipse, you have two of these focus points. The “long” part of the ellipse is the major axis and the “short” part is the minor axis. Shown above is a fun animated diagram from Wolfram MathWorld that illustrates how this works.

And finally, an ellipsis is the sequence of three dots indicating one or more words have been omitted, particularly (but not necessarily) from a direct quote. The word “ellipsis” also refers to the actual omission itself or the act of omitting those one or more words, with or without the three dots (or other equivalent mark).

For instance, if the original quote is, “The key to success, I guess you could say, is keeping an open mind,” then you could shorten the line using an ellipsis to become, “The key to success…is keeping an open mind.” The three dots could also be used simply to signify a pause.

So, to summarize:

  • An eclipse refers to blocking light.
  • An ellipse is an oval.
  • An ellipsis signifies omitted text.

Once upon a time I was falling in love, but now I’m only falling apart. And there’s nothing I can do. A total eclipse of the heart…