Last year saw the most recent transit of Venus, as our planetary sibling passed directly between the Sun and our planet. It's an exceedingly rare event—the next one isn't due until 2117, and that's actually a bit ahead of the normal schedule. But what exactly is the Transit of Venus? In a sense, it's just a really poorly positioned solar eclipse.
That's the rather amusing take put forward by the astronomers at NASA's Astronomy Photo of the Day, and this gorgeous ultraviolet image of the Sun and Venus during the transit helps illustrate the point. Specifically, Venus at this point is exactly in line with the Sun and Earth, which makes this the equivalent of an annular eclipse. We almost always think of solar eclipses as when the Moon is so positioned that it temporarily blocks out our view of the Sun, but there's no theoretical reason why the astronomical body doing the blocking has to be the Moon.
Of course, there's a hugely important practical reason why that's the case — while the Moon is much, much smaller than Venus, it's also much closer to Earth, so its relative size in the sky makes it possible for it to blot out the Sun entirely, with our star leaving only a bright surrounding outline known as the ring of fire. This Venusian eclipse, on the other hand, only managed to cover up the tiniest fraction of the Sun, leaving uncovered what the astronomers refer to, tongue firmly in cheek, as "an extraordinarily large ring of fire."
To see the full image and for a full explanation as to how this ultraviolet image was taken, check out the APOD site.
Image Credit: NASA/SDO & the AIA, EVE, and HMI teams; Digital Composition: Peter L. Dove