This is the Dudley Observatory Skywatch Line for Wednesday, January 2nd, and Thursday, January 3rd, written by Louis Suarato.
The 11% illuminated, waning crescent Moon sets at 2:21 p.m., Wednesday. Mars, in the constellation Pisces, begins January at magnitude 0.50, but will fade to magnitude 0.90 at month’s end. Mars Insight, NASA;s robotic lander, recently placed the first seismometer on the planet, enabling scientists to detect Marsquakes. The pre-dawn planets of Mercury, Jupiter and Venus, are joined by the crescent Moon. Thursday morning, the 6% illuminated, waning crescent Moon will be 3 degrees to the left of Jupiter. Venus is descending, while Jupiter is climbing each day, and the two planets will pass each other on January 22nd.
Earth reaches perihelion, its closest approach to the Sun during 2019, on Thursday at midnight. The Sun will be 91,403,724 miles away when Earth’s elliptical orbit brings it to its closest approach. During aphelion, which occurs every year around July 4th, Earth is approximately 3.1 million miles further away from the Sun than it is during perihelion. This change in distance isn’t enough to cause a seasonal change to our planet. The 23.5 degree tilt of our planet’s axis is what causes the seasonal changes to the hemispheres. During perihelion, when Earth is closest to the Sun, its northern hemisphere is tilted away from the Sun, lengthening the time it takes for sunrays to reach Earth. When the northern hemisphere tilts toward the Sun in July, the more direct sunrays warm the upper half of the planet.
Comet 46P/Wirtanen is still providing excellent binocular and telescope views. Now shining at 4th magnitude, this comet is heading back toward Jupiter’s orbit. Thursday night, you can use the top two stars forming the Big Dipper’s bucket to find Comet 46P/Wirtanen. Follow the two stars, Megrez and Dubhe, toward Capella. You’ll find the bluish-green comet about a third, to half, of the way to Capella.