Two nights ago on July 26 I could still spot NEOWISE without optical aid as long as I knew where to look. I could even make out a 3° tail which increased to 6° in binoculars. Last night, under the 8-day-old moon, the comet was fainter and more difficult, and it won’t get any easier in the coming nights. The comet’s increasing distance from the Earth and the waxing moon will soon render it invisible with the naked eye. There’s good news, too. The bright head should remain visible in binoculars past the August 3rd full moon and for a time beyond.
While the Dipper is still a handy reference for finding NEOWISE I now use the star Cor Caroli — Latin for “Heart of Charles” — in the small constellation Canes Venatici the hunting dogs. You’ll find the star just off the Dipper’s handle. Its name honors either King Charles I of England, who was beheaded in 1649 during the English Civil War, or his son Charles II, who restored the monarchy in 1660. At the time no one knew it was a beautiful double star for a small telescope, otherwise both kings could have been included. If you have a scope by all means look at this gem.
Jupiter and Saturn now dominate the southern sky at nightfall. This last week Mars joined them. The Red Planet now rises before midnight in the southeastern sky in the constellation Pisces. Pisces’ lack of any bright stars makes Mars stand out all the more. Tonight it gleams at magnitude –1, not much fainter than Sirius, the brightest star in the sky.
Through my telescope at dawn July 28, I was struck by the icy beauty of its south polar cap, a feature visible even in a smaller 4 to 6-inch telescopes. Temperatures are so cold at Mars, around 200° F below zero (–129° C) at the poles, that carbon dioxide freezes out as snow and ice. That’s what you see through the telescope — a pure white button of carbon dioxide (dry ice) at the south end of the planet. Think of it as a dry-ice version of Antarctica.
Lower your gaze and look in the eastern sky, and you’ll jump from a cold planet to a hot one. That’s where Venus hangs out these mornings. This unmistakably bright object comes up well before the sun and can’t be missed. Its brilliance is due both to perpetual cloud cover and proximity to the Earth. Jupiter is just as cloudy and more than 11 times larger but so much farther away it’s six times fainter.
On Venus, the clouds and thick CO2 atmosphere trap the sun’s heat, driving the surface temperature there to 880° F (470° C), way hotter than a typical oven. Venus stands furthest from the sun on August 13 so it’s really easy to see right now. On the 15th the planet joins the crescent moon in a spectacular conjunction.