Skywatch Line for Wednesday and Thursday, May 15 and 16, 2024, written by Alan French
This is Dudley Observatory’s Skywatch Line for Wednesday and Thursday, May 15 and 16, 2024, written by Alan French.
The Sun rises at 5:32 A.M. on Wednesday and sets at 8:12 P.M. On Thursday it rises at 5:31 and sets at 8:13. This Thursday has just over 15 more minutes of daylight than last Thursday.
The Moon reached first quarter on Wednesday morning and began moving toward full. The Moon will be due south and high in the sky at 7:37 P.M. Wednesday. By 9:30 it will be toward the southwest, 52 degrees above the horizon, and its visible face will be just over half in sunlight. This is an excellent time to explore the Moon with a telescope or even binoculars. Even a very modest astronomical telescope or spotting scope will reveal a wealth of detail. Although the Moon is essentially unchanging, the lighting of the lunar landscape changes as the Sun moves across the lunar sky.
As we move from new to full Moon the terminator, the line between sunlight and darkness, is the sunrise line, marching across the lunar landscape, bringing new features into view, and changing the lighting and shadows of those already in sunlight. Near the terminator shadows are long and detail stands out in bold relief. Away from it shadows grow shorter as the Sun’s altitude increases and details become more subtle. It is fascinating to watch these changes. I often visit a few features and then go back and revisit each later to see how their appearance has changed.
On Thursday night, the Moon, 65% sunlit, is due south just after sunset. At 9:30 it will be high toward the south southwest, 52 degrees above the horizon. The terminator will be farther east (sky east) and more features will be in sunlight. A higher Sun will be illuminating features that were near the terminator Wednesday night, changing their appearance.
Skies here were not great here on Friday night, May 10, when a geomagnetic storm, the strongest in more than two decades, triggered an exceptional display of the aurora borealis or northern lights. Such shows are usually visible, at best, only in the northern states, but this was seen in all 50 states and even farther south. Despite clouds and generally poor skies, I have seen many reports of people in the Capital District and surrounding region who were able to catch some of the light show through clear patches and areas with thinner clouds. A common question is “Why didn’t I see color,” or “Why do the photos show such vivid colors, compared to what I saw?”
Today’s digital cameras are very good at taking photographs in low light, and are far more sensitive to color than our eyes. It is a big selling point since people like to take photos wherever they go. As you know, when you are outside at night enjoying the night sky, or wake up in a dark room, you can see in low light, but color vision is lost. Our dark adapted eyes are far more sensitive to light, but we see in black and white. Auroras can appear colorful by eye, but they must be brighter for our eyes than for a digital camera. Cameras can also take longer exposures, gathering more light than our eyes and further enhancing colors. (The effective exposure time of the human eye is approximately 1/15th of a second.)