Astronomy Picture of the Day . ... Star Trails over El Capitan . ... To celebrate, consider this remarkable image following the Sun's yearly trek through planet Earth's sky, the first analemmas exposed every day through the technique of solargraphy. ... When does the line between day and night become vertical? ... At an equinox, the Earth's terminator -- the dividing line between day and night -- becomes vertical and connects the north and south poles. ... The Antennae Galaxies in Collision . ...