Jupiter and Saturn will appear just one-tenth of a degree apart, or about the thickness of a dime held at arm’s length, during the winter solstice tomorrow night. It is the first conjunction between the two planets in 20 years and the closest they could be seen in the sky together in nearly 800 years.

Of course they won’t be as close as it will appear. In fact, the two planets will still be separated by mindboggling 453.6 million miles.