A tail to remember?

Our slanted view of the comet’s evolving tails is perfect. The gas tail glows from atoms ionized by ultraviolet light and blows straight back (away from the Sun) in the solar wind. Appearing gray to the human eye at first, the familiar green hue in March’s images effloresces into a brilliant emerald even in 8-inch scopes. It may transition to blue as ionization ramps up. Look for kinks in the turbulent flow and remain on the alert for the gas tail breaking during a “disconnection event,” when the tail appears to break away and then reforms a short time later. Spaceweather.com may publish advance notice of the celestial barber cut.The dust tail spreads out from the core in a narrow sail-shaped fan, curving away from Polaris and up toward the Big Dipper. A really dark sky can double the length compared to a typical observing site. Look for striations — streaks resulting from the periodic ejections of dust as active spots rotate to face the Sun, turning on and off with each spin. The big unknown: Is Y4 ATLAS a lightly powdered rubble pile that produces a meager tail that dissolves into nothingness? Or does luck strike us with a dust-choked snowball whose tail forms the magnificent sword we see in paintings of old? A touch of aurora or noctilucent clouds would really top off the light show.Use a range of magnifications. Crucially, zoom in to the core as much as the seeing conditions allow. Comet Hale-Bopp produced spiral jets that visibly changed in an hour for patient observers using high power.Grandparents’ stories about a comet they saw when they were kids will be about the tail, not how bright the head was. Extra-bright tails happen when the dust lies between us and the Sun. That’s because in such a configuration, the tail takes the sunlight from below the horizon and scatters it forward. In 2006, Comet McNaught’s spectacular tail occurred with a low angle of 32°. For ATLAS, our viewing geometry of 48° gives a modest 1- to 2-magnitude enhancement — still mighty fine.