Driftless Dark Skies: Galileo! Galileo!

February 11th, 2019 by John Heasley

February 15 is the 455th birthday of Galileo Galilei. He is beloved by stargazers because he was the first of us to observe the starry sky with a telescope and to share the news with the world that the Milky Way is full of stars, the Sun has spots, the Moon is a world, Jupiter has moons, Venus has phases, and Saturn has “ears”.

In the fall of 1609, Galileo turned his telescope to the Moon and was amazed by what he saw. His book, Sidereus Nuncius “Starry Messenger” conveys the excitement of discovery. “These sights, though unknown, are not entirely unfamiliar however. It is most beautiful and pleasing to the eye to look upon the lunar body from so near. Anyone will then understand with the certainty of the senses that the Moon is by no means endowed with a smooth and polished surface, but is rough and uneven and, just as the face of the Earth itself, crowded everywhere with vast prominences, deep chasms, and convolutions.” Galileo’s starry message is that the Moon is not a perfect unworldly sphere as once thought, but a world with mountains and craters and plains. The art education he received earlier in life allowed him to see clearly the patterns of light and shadow on the Moon and to know that he was watching morning sunlight illuminating the rims of craters and tips of mountains as they cast shadows across the landscape.

February is a great month to see the Moon through the eyes of Galileo. Ordinary binoculars are closest in size and magnification to the telescope Galileo crafted and used four centuries ago.  Begin the morning of Feb. 1 when the Waning Crescent Moon is in the southeast sky between Venus and Saturn. The following morning, the Moon has waned even more and moved closer to Saturn. Best view in the Driftless is 6-6:30am. Be sure to notice the Earthshine on the dark side of the Moon and how the shadows heighten the features along the terminator–the line separating light/dark and night/day where the Sun is setting on the lunar landscape.

The Moon is too close to the Sun in the days around New Moon (February 4) to observe, but look for it again the evening of February 6 in the southwest after sunset at 5:18 and before moonset at 7:09. Now the terminator marks where the Sun is rising on the Moon as craters and mountains are illuminated at dawn. On February 10, the Moon is the same phase (about a third illuminated) as it was on July 20, 1969 when Neil Armstrong and Buzz Aldrin explored the Sea of Tranquility as the Sun was rising there. You can spot this darker area just to the right of the terminator along the lunar equator halfway between the “horns” of the Moon. Just above the Moon is ruddy Mars. In one binocular view, you can see the world where humans once walked and the world where we might next walk.

On the night of February 12, the terminator equally divides the First Quarter Moon. On February 15, celebrate Galileo’s birthday by enjoying the Waxing Gibbous Moon just above Orion the Hunter and surrounded by the bright stars of the Winter Circle. The Full Snow Moon on February 19 is an excellent time to see the three great ages of lunar geology. The light areas are the lunar highlands with the original crust of the Moon from the Age of Formation. The craters and the rays of ejecta cast out from them are from the Age of Bombardment. The dark areas are maria, basaltic plains from the Age of Lava Seas.

Last Quarter is February 26, and now the terminator dividing the two halves of the Moon marks where night is falling. On the morning of February 27, Jupiter is right below the Waning Gibbous Moon. Best view is after moonrise at 2:04 and before sunrise at 6:41. If you can hold your binoculars steady enough, you might be able to glimpse the four Galilean Moons of Jupiter first discovered by Galileo—Io, Europa, Ganymede, and Callisto.  Magnifico!

If weather allows, there will be Candlelight Hiking, Snowshoeing, Skiing, and Stargazing at Wildcat Mountain State Park on 9 Feb (5-8pm) and Wyalusing State Park on 16 Feb (6-9pm).

John Heasley is an astronomy educator and stargazer who enjoys connecting people with the cosmos. He volunteers with NASA/JPL as a Solar System Ambassador. For more information about stargazing in southwest WI, like Driftless Stargazing LLC on Facebook and find out whenever there’s something awesome happening in the skies. Driftless Dark Skies appears monthly in the Voice of the River Valley.