March 19, 2023
Sunday, March 19, 2023
Just one more day left of the winter season, according to the calendar. The beginning of spring happens when the mid-point of the sun is on the celestial equator—the projection of Earth's equator onto the sky. On March 20 at 2:24 PM, the sun crosses from south of the celestial equator to north of the celestial equator. This day is also called the March equinox.
“Equinox” means “equal night” because the amount of daylight is supposed to equal the amount of night time all over the planet. I say “supposed to” because the actual time when the 12 hours of daylight between sunrise and sunset was a few days earlier. The sun has a noticeable angular size, instead of being a pinpoint. Sunrise happens when the top of the sun's disk pokes above the horizon and sunset happens when the top of the sun goes below the horizon. The bending of light (refraction) as it passes through the atmosphere means that we'll see the sunrise a few minutes before and sunset a few minutes later than if there was no atmosphere at all. The atmospheric refraction is much more noticeable for objects close to the horizon because you're looking through more atmosphere than if the object is high above near overhead at the zenith.
This year, a new moon will happen just one day after the March equinox (i.e., on March 21). The following evening on March 22, a razor-thin waxing crescent moon will be only 1.5 degrees (about a thumb-and-a-half width at arm's length) from bright Jupiter. Should be a nice sight!
On the evening of March 27, you may be able to spot Jupiter less than 1.5 degrees from Mercury very low in the west just after sunset. You'll probably need to use binoculars to pick them out from the twilight glow. Near the end of the month on March 28, the moon will be at first quarter phase among the stars of Gemini.
In the early pre-dawn morning sky, the ringed planet, Saturn, is now becoming visible in the east. This morning, the waning crescent moon was about half a fist width below Saturn. Over the next several months, Saturn will appear higher and higher in the eastern pre-dawn sky.
In astronomy research news was a report about the increasing occurrence of the broadband internet satellites streaking across the field of view of the Hubble Space Telescope. The Starlink, OneWeb, and Project Kuiper satellite constellations will each have many thousands of satellites positioned above the Hubble Space Telescope's orbit around Earth. When they cross the field of view of the Hubble Space Telescope, a bright streak appears in the image Hubble was taking.
Research telescopes on the ground have already been contending with satellite constellations for a while now. While one or two bright streaks can be edited out, many tens to hundreds of streaks can't be. Back in 2021 with just 1562 Starlink satellites in orbit, there was a 5.9% chance of a Starlink satellite crossing the field of view. That proportion is only going to increase as more satellites are launched to get to the 12,000 planned for Starlink. OneWeb is going to put up nearly 6400 satellites and Project Kuiper will eventually have over 6200 satellites in its network. In order to continue doing cutting-edge astronomy research, we may need to build telescopes on the moon at a huge expense!