RISING MOON
I Breaking down
THE WAXING GIBBOUS Moon is chock-full of interesting sights. You can even start your observing session before dark, when the light blue sky reduces glare. Take in Tycho’s long rays as well as the large expanse of Mare Imbrium and eye-catching Sinus Iridum on its northwestern portion. Then follow that up with the prominent crater Copernicus’ splatter.
At night the Moon is remarkably bright in a scope. A filter is best to cut down the light, though reducing the aperture with a mask or wearing sunglasses can help a lot, too.
On the evening of the 19th, a few days before Full, the sunrise line has moved past the fascinating crater Gassendi, perched on the north edge of the modest Mare Humorum in the lunar southwest. Formed by an impact event, Gassendi is a 70-mile-wide circular feature tilted down toward the center of the Sea of Moisture. The slumping of the lava-filled basin dragged the surrounding terrain down with it.
Gassendi has multiple peaks and slumped walls, characteristics of large craters. You can even see how the prominent crater on its north side formed afterward and pushed this material inward. The arcs and rilles inside the main ring to the south and southeast are leftovers of floor fracturing, where the up-and-down movement of the crust caused cracks like those you might find on a pie crust. Lava welled up from underneath, covering half the floor — though not as deep as the fully coated crater Plato far to the north.
A contemporary of Galileo and Kepler, Pierre Gassendi of France was a supporter of Copernicus’ heliocentric theory.