Explanation: A new comet is brightening and is now expected to become visible to the unaided eye later this month. C/2009 R1 (McNaught) is already showing an impressive tail and is currently visible through binoculars. The above image, taken yesterday from the Altamira Observatory in the Canary Islands and spanning about five degrees, shows an impressive green coma and a long ion tail in front of distant star trails. Although predicting the brightness of comets is notoriously difficult, current estimates place Comet McNaught as becoming visible to unaided northern hemisphere observers in late June, before sunrise, and in early July, after sunset. Discovered by Robert McNaught last year, the sun-orbiting iceberg will pass the Earth next week and will continue to melt and shed debris as it closes in on the Sun until early July. After reaching about half of the Earth-Sun distance from the Sun, the comet should fade rapidly as it then heads out of the inner Solar System.