"The comet's tail is about 2.5 degrees long," says Rhemann.
That means it spans more than 8 million km. For comparison, the entire sun is 1.4 million km wide; you could wrap the comet's tail around the sun's equator twice. Another way of putting it: The distance from Earth to the Moon is only 5% of the length of the gaseous lane behind Comet PanSTARRS.
The comet's outburst is probably caused by a fresh vein of icy material in the comet's nucleus exposing itself to solar radiation. Furiously vaporizing, the comet's core is spewing jets of dust and gas into space--a tail-building process that should intensify as the comet approaches the sun between now and early May.
The comet's closest approach to Earth will be 176 million km (1.18 AU) on April 19th. Even at that distance, the comet might be a beautiful sight in backyard telescopes if current trends continue. Stay tuned!