While it may feel like we’re stuck in a repeating loop of Spring 2020, watching the night skies can remind us that the seasons do actually keep passing by. Indeed many cultures throughout history have used the night skies to mark the passing of time. In my home country of England, ancient peoples built Stonehenge, probably to track the motion of the Sun (the brightest star in the sky!) and mark the year. In New Zealand, the Maori used the first sighting of Matariki (also known as the Pleiades) to set the start of the new year. The hottest part of late summer in the Northern hemisphere is termed the “dog days of summer” because the Sun is in the same part of the sky as the “dog star,” Sirius.
For me, the most obvious change in the night skies has always been the annual appearance and disappearance of Orion. In the early part of the spring semester, this iconic constellation has had center stage in the sky, rising in the Southeast at dusk and traveling across the southern skies to the west as the Earth turns in its daily motion. By the end of the semester, however, it will disappear into the sunset and be invisible for another year.
Orion is one of my favorite constellations, partly because it is one of the easiest to pick out in the sky, but also because includes two of the brightest stars in the skies: Betelgeuse, the redder star at the upper-left of the constellation, and Rigel, the blue supergiant at lower-right. Students in my classes know I like to use this pair (along with the binary stars Alberio, which you can only see through a telescope) as an example of how they can see for themselves that stars have different colors, set by their surface temperature. While our eyes are not good at seeing color at low light levels, sometimes we can pick out a faint hue, like in the reddish color of Betelgeuse, which in contrast to the bluish white-hot supergiant Rigel is a relatively cool red supergiant star.
Every human on Earth looks up at the same skies, although their perspective depends a little bit on exactly when and where they are. I remember visiting the Southern Hemisphere once and being pleasantly surprised to see Orion inverted relative to how I had been used to seeing it. It makes complete sense once you think about it, since we don’t live on a flat Earth, our perspective relative to the skies changes significantly when we move in latitude (towards or away from the Equator).
Of course, the constellations we name in astronomy are entirely human inventions, a giant dot-to-dot puzzle in the skies. We now know that the bright stars that ancient Greek astronomers joined together into the constellation Orion, vary from 245 to over 1300 light years away from us, not physically connected at all, apart from all being in the same Galaxy as the Sun! To explore how various different cultures have drawn different patterns in the night skies you might like to visit Figures in the Sky, which is a beautiful example of artistic data visualization. And if you prefer just to look up at the skies you can enjoy stargazing and inventing your own patterns.
Happy Stargazing, and keep looking up.
Spring 2022 Stargazing Calendar
March
1st: Possible date for launch of NASA Capstone Mission to the Moon
2nd: New Moon
12th: Possible date for launch of NASA Artemis-1 Mission, testing human spacecraft to return to the Moon
18th: Full Moon (the “Worm” Moon)
20th: Spring Equinox, 11.33am ET
20th: Venus at Greatest West Elongation (best chance to see in the morning before sunrise)
April
1st: New Moon (no joke)
Launch of Japanese mission to the Moon, SLIM expected in April.
16th: Full Moon (the “Pink” Moon)
22/23rd: Lyrid Meteor Shower – the Moon is partially lit, and this peaks early in the morning of the 23rd, so not likely to be an easy one to watch.
29th: Mercury at Greatest East Elongation (best chance to see in the evening after sunset)
30th: Second New Moon of the Month (a “Black Moon”), and a partial Solar Eclipse (but not visible from Haverford)
May
Launch of an expansion of the Chinese Space Station, Tiangong expected in May
5/6th Eta Aquarid Meteors – this shower, which comes from debris from Halley’s comet, has a possibility of being quite impressive this year, possibly not just on the peak night, but for a few days either side.
16th: Full Moon (the “Flower” Moon), and Lunar Eclipse
30th: New Moon