Skywatch Line for Wednesday and Thursday, January 10 and 11, 2024 written by Alan French
This is Dudley Observatory’s Skywatch Line for Wednesday and Thursday, January 10 and 11, written by Alan French.
The Sun rises at 7:25 A.M. on Wednesday and sets at 4:40 P.M. On Thursday it rises at 7:25 and sets at 4:42. This Thursday has just under 8 ½ minutes more daylight than last Thursday.
The Moon reached last quarter on Wednesday, January 3, and will reach new Thursday morning. The Moon is too close to the Sun to spot over these two days.
Mercury was highest in the morning sky on Monday and remains visible about 40 minutes before sunrise. You will need a good view to the southeast and transparent skies. If sky conditions are less than ideal,
binoculars may be needed to spot Mercury.
To find Mercury, look toward the southeast at 6:45 A.M. Bright Venus will be easy to spot, 16 degrees above the horizon. On Thursday morning fainter Mercury will be 12 degrees to Venus’ lower left. If you imagine Venus as the center of a clock, Mercury will be about half way between the 6 o’clock and 9 o’clock positions. (Remember that a fist, held at arm’s length, spans 10 degrees across the knuckles.) On Friday morning, Venus will be slightly lower at 6:45 and Mercury a little closer. If you can not spot Mercury by eye, try looking with binoculars. Be sure to carefully focus on a star first. Vega should still be visible in the east northeast. (Venus can be a tempting target to focus on, but its brightness can make it hard to pinpoint best focus.)
Jupiter, moving slowly among the stars, continues in the evening sky. On Wednesday it is due south and highest, just under 60 degrees high, at 6:51 P.M. On Thursday the gas giant transits at 6:47 P.M. The hour
around its transit time and highest appearance is ideal for viewing detail on Jupiter with a telescope. We often also get a period of steady skies in the hours just after sunset.
As we have mentioned, any telescope can easily reveal Jupiter’s brightest four moons, appearing as stars to either side of the planet. A magnification of 20 to 30 times should be sufficient, but 50 to 60 power
will move them farther from the planet and each other. The four moons, Io, Europa, Ganymede, and Callisto were discovered by Galileo and are known as the Galilean moons. He discovered them in either December, 1609, or January, 1610, and recognized they were moons orbiting the planet in March of 1610.
On Wednesday around 6:50 P.M. Io and Ganymede will be close together to Jupiter’s east, with Ganymede farthest away. Europa and Callisto will be farther apart to the west, with Callisto farthest away. If you see a fainter star closer than the moons to Jupiter’s east, it is an 8th magnitude star. All the remaining Jovian moons are beyond the reach of a typical amateur’s telescope.
On Thursday night around 6:50 P.M. Ganymede will be well to Jupiter’s east and Callisto just slightly east and above the planet, not far from the planet’s limb. Europa and Io will be to the west, close together,
with Europa closer to the planet. That 8th magnitude star, if you can spot it, will be roughly in line with Io and Europa and closer to the planet. It nicely shows how much Jupiter has moved against the stars in
24 hours.