Green Comet On It's Way

"Perhaps it's a comet." Still frowning, Bob Star swung back toward the observatory. "It looked like one - it was a short streak of that queer, misty green, instead of the point a star would show..."
Inside the chilly gloom of the observatory, Bob sat down at the telescope. Its mechanisms whirred softly, in swift response to his touch. The great barrel swung to search space with its photoelectric eyes, and the pale beam of the projector flashed across to the concave screen.
...He stepped up the electronic magnification. Vindemiatrix and the fainter stars slipped out of the field. The comet hung alone, and swiftly grew. Its shape was puzzling - a strangely perfect ellipsoid. A greenish football, he thought, kicked at the System out of the night of space - by what?"

In the 1936 novel "The Cometeers" by Jack Williamson (The Legion of Space takes a mad gamble to save the solar system from an inhuman, invincible invader!) it's not a very happy day for earth as the 'comet' turns out to be "an alien force field millions of miles in extent, containing worlds enslaved by the Cometeers, an alien race of energy beings." Yikes!

But we have a new comet discovered by a guy named Lovejoy in Australia, and the visitor is a nice green color caused by cyanogen and diatomic carbon in the coma. It's coming in almost perpendicular to the ecliptic, meaning it's coming into the solar system from below and will be visible to people in the northern hemisphere early next month. By late April it will be 40 million miles away and is expected to brighten.