article_snippet: Such eclipses are basically as old as the galaxy itself, happening when the moon and sun are at just the right distance from the Earth and the moon and sun appear to be of the same apparent size in the sky -- even though the sun is actually about 400 times larger.
article_snippet: An eclipse happens when the moon passes right in front of the sun, blocking the sunlight and casting a shadow on the Earth.
article_snippet: That means what used to be morning suddenly looks like nighttime again, until the sun and moon get out of each other's way.
article_snippet: Staring at the sun anytime can be a bit dangerous, even when it's there, not there, then there again during an eclipse.
article_snippet: That's where the term "eclipse blindness" -- which is really retinal burns -- comes from.
article_snippet: That means there will come a time when the moon will appear to be too small to cover the sun.
article_snippet: But don't sweat the moon just yet
article_snippet: : NASA calculates this will take about 563 million years, meaning there's still time to catch another eclipse.