Skywatch Line for Wednesday and Thursday, January 8 and 9, 2025, written by Alan French

This is Dudley Observatory’s Skywatch Line for Wednesday and Thursday, January 8 and 9, 2025, written by Alan French.

The Sun rises at 7:25 A.M. on Wednesday and Thursday, and sets at 4:39 P.M. on Wednesday and 4:40 on Thursday. Thursday gained 7 minutes 50 seconds of daylight compared to last Thursday. The weekly increase continues to grow as the Sun moves farther north.

The Moon reached first quarter on Monday and is how headed toward full. On Wednesday night, as darkness falls, look for a bright, gibbous Moon high in the east southeast. By 6 P.M. it will be 60-degrees above the southeastern horizon and its visible face with by 72% in sunlight. The Moon will set at 3:10 A.M. on Thursday morning.

On Thursday at 6 P.M. the now 82% sunlit Moon will be 55 degrees above the east southeastern horizon. It will set at 4:28 A.M. Friday. The Moon will reach full late Monday afternoon, January 13.

Venus continues to dominate the southwestern sky as darkness falls, and will be 25-degrees above the horizon at 6 P.M. Venus is our nearest planetary neighbor, but is a disappointment through a telescope, its surface obscured by thick, reflective, generally featureless clouds. Because it is closer to the Sun than our Earth, it shows phases like our Moon. Planets farther from the Sun can only show modest, gibbous phases. Mars is the only superior planet that can show an obvious gibbous phase

from our vantage point.

Venus, on its faster, inner orbit, completes its trip around the Sun in 224.7 days, compared to our Earth’s year of just over 365 ¼ days. Venus was last on the opposite side of the Sun from Earth on June 4, 2024, when it was 259.6 million km (161.3 million mi) from Earth. (When an inferior planet is on the opposite side of the Sun, it is at superior conjunction with the Sun.) Through a telescope, had it not been hidden

by the Sun, Venus would have appeared 9.6 arcsec in diameter and its entire sunlit face would have facing toward Earth and visible. Because the orbits of the Earth and Venus are not in quite the same plane, Venus is not always hidden by the Sun at superior conjunction, it may be slightly north or south of the Sun – and too close for safe observation. At eight of the forty superior conjunctions between 1980 and 2040, inclusive, including the last one, Venus was behind the Sun from Earth. The Sun occulted Venus.

Since superior conjunction, Venus has been slowly catching up with Earth. As it does, it grows closer and we see less of the sunlit half. It is now 102.4 million km (63.6 million mi) away, appears 24.4 arcsec in diameter, and we see just over half (51.1%) of its sunlit face through a telescope.

Venus will continue catching up with Earth in the coming weeks. The telescopic view will grow and less of the sunlit face will be visible. On February 9, Venus will be 68.7 million km (42.7 million mi) away, and appear 36.3 arcsec across and 31.4% sunlit. By March 9 it will be 45.4 million km (28.2 million mi) away, appear 55.0 arcsec across and only 6.8% sunlit, a lovely crescent.

By March, Venus will be moving rapidly lower in the evening sky. By March 9 Venus will be 14 ½ degrees high at 7:30 P.M., just over a half-hour after sunset. A week later, on March 16, Venus will be 6 ½ degrees above the horizon at 7:30 P.M., a little less than half-hour after sunset. These weeks will be the best time to catch a telescopic view of a crescent Venus soon after sunset.

Venus will pass roughly between Earth and the Sun on March 22, passing just over 8 degrees north of the Sun. When an inferior planet is on the same side of the Sun as Earth, and in line with the Sun, it is at inferior conjunction. At inferior conjunction, Venus will set just 15 minutes after the Sun. Venus will be 42.0 million km (26.1 million mi) from Earth. It would appear 59.4 arcsec in diameter and be an extremely

slender crescent, just over 1% sunlit.

Unless you are an experienced observer with a telescope that can be accurately pointed at Venus, like a properly aligned and setup GoTo telescope, observing the planet when it is near the Sun and the Sun is still visible, should NOT be attempted. An accidental view of the Sun through a telescope can cause partial, permanent blindness. (Telescopes should never be pointed at the Sun without a filter specifically

designed and made for solar observing. Filters should be securely mounted and solar telescopes should not be left unattended. Those new to solar observing should seek expert advice.)

Observing the Sun or observing near the Sun requires care, proper equipment, preparation, and expertise. Your vision is too important to risk!

At the 38 inferior conjunctions between 1980 and 2040, inclusive, Venus only passed in front of the Sun, a transit, twice. Transits of Venus are rare events. The next transit of Venus will not occur until December, 2117.