Green comet makes closest approach to earth

On Sept. 10th, Comet 21P/Giacobini-Zinner ("21P" for short) will make its closest approach to Earth in 72 years--only 58 million km from our planet. This small but active comet is easy to see in small telescopes and binoculars as it shines like a 7th magnitude star. Michael Jäger of Weißenkirchen, Austria, sends this photo of 21P passing through the stars of Auriga on Sept. 7th.

Taken by Michael Jäger on September 7, 2018 @ Weißenkirchen Austria. Comet 21P /Giacobini-Zinner at 00.55 UT, 10x3min filter UV/IR, 5x210 blue 210 green 210 red ASA 8/2.8 Asi 1600 1x1bin

The close approach coincides with a New Moon, providing a velvety-dark backdrop for the passage of the comet. The best time to look is during the dark hours before sunrise when the constellation Auriga is high in the eastern sky. If you have a GOTO telescope, use these orbital elements to point your optics. Detailed sky maps can help, too.

Shining just below the limit of naked-eye visibility, the comet will remain easy to photograph for the rest of September. If you can only mark one date on your calendar, however, make it Sept. 15th. On that night, 21P will cross directly through the middle of the star cluster M35 in the constellation Gemini. Astronomer Bob King writing for Sky and Telescope notes that "the binocular view should be unique with the rich cluster appearing to sprout a tail!"

21P/Giacobini-Zinner is the parent of the annual Draconid meteor shower, a bursty display that typically peaks on Oct. 8th. Will the shower will be extra-good this year? Draconid outbursts do tend to occur in years near the comet's close approach to the sun. However, leading forecasters do not expect an outburst this year despite the comet's flyby. In case they are mistaken, many eyes next month will be on the shower's radiant in the constellation Draco.