Event Date: May 18th
Time: 8:45 PM
Brief
I have come back to the Winter Circle a couple of times since its peak evening positioning during the namesake season. Now that we are in the second half of spring, a little over a month before the summer solstice, we see the constellations and stars of the Circle setting either before or after nightfall. Although they are just becoming visible in the glare of the Sun, with some requiring binoculars until about 15-30 minutes later, we see some of the stars still high enough in [altitude].
Detailed
Look at the celestial grid and equator included in the image, to remind us of the different declinations of each star still high enough to see: Sirius is the furthest south, so it is just barely above the horizon and hardly visible despite being very bright. Rigel, being south and further west of some of the others, is already set. When navigators first saw these 1st magnitude stars appear in the winter and spring evening skies, it further defined the nautical period of twilight. The time for the image marks the beginning of this twilight period, which varies in length with the seasons and the Sun's position to the horizon once set. The same goes for civil and astronomical twilight, and I will talk about those in a little more detail next month.
Among the stars is Venus, which outshines all of them by dozens of times. At 2º from star El Nath, which I introduced about a week ago, the planet will move among the Winter Circle stars as it picks up retrograde rate and quickly plunges towards the Sun's glare over the next two weeks, eventually disappearing from sight and waning to a very thin crescent right before inferior conjunction.
Time: 8:45 PM
Brief
I have come back to the Winter Circle a couple of times since its peak evening positioning during the namesake season. Now that we are in the second half of spring, a little over a month before the summer solstice, we see the constellations and stars of the Circle setting either before or after nightfall. Although they are just becoming visible in the glare of the Sun, with some requiring binoculars until about 15-30 minutes later, we see some of the stars still high enough in [altitude].
Detailed
Look at the celestial grid and equator included in the image, to remind us of the different declinations of each star still high enough to see: Sirius is the furthest south, so it is just barely above the horizon and hardly visible despite being very bright. Rigel, being south and further west of some of the others, is already set. When navigators first saw these 1st magnitude stars appear in the winter and spring evening skies, it further defined the nautical period of twilight. The time for the image marks the beginning of this twilight period, which varies in length with the seasons and the Sun's position to the horizon once set. The same goes for civil and astronomical twilight, and I will talk about those in a little more detail next month.
Among the stars is Venus, which outshines all of them by dozens of times. At 2º from star El Nath, which I introduced about a week ago, the planet will move among the Winter Circle stars as it picks up retrograde rate and quickly plunges towards the Sun's glare over the next two weeks, eventually disappearing from sight and waning to a very thin crescent right before inferior conjunction.
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| click on images to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp. |
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