Eyes to the Sky: Sirius, The Big Dog, and Thor’s Helmet

January 25 – February 7, 2021

Mount Washington — Sparkling, blue-white Sirius the Dog Star, the brightest star in the night sky, rises in the east-southeast 20 minutes after sunset this evening and will rise simultaneously with sunset by month’s end. As twilight deepens, Sirius — from the ancient Greek Seirios for “scorcher” or “glowing” — appears above the hilly Berkshire skyline leading one of winter’s most alluring constellations, The Big Dog, into the sky. As the brightest star in Canis Major, Sirius bears the designation Alpha Canis Majoris. The Dog Star’s brilliance, -1.46 magnitude, is partly due to its being one of our solar system’s closest neighbors among the stars, at 8.6 light years distant. By contrast, the cosmic phenomenon, Thor’s Helmet, pictured above, is about 12,000 light years distant.

The constellation Canis Major contains Sirius, the brightest star. The constellation suggests the outline of a dog, sometimes fancied to be the dog accompanying Orion (the Hunter).

As a mostly naked-eye stargazer following The Big Dog’s trajectory from nightfall in the southeast until after midnight in the southwest, I was intrigued when an amateur astronomer introduced me to Thor’s Helmet, an emission nebula*, that, when viewed with a telescope from Earth, is located in, or close to, the boundaries of Canis Major. I queried Kent DeGroff, the creator of our image of Thor’s Helmet, about how he works. I am stretching my understanding simply to relate a paragraph that gives us access to his experience of reaching out to the cosmos with a camera equipped to gather images of celestial phenomena and work to make them accessible to viewers.

From correspondence with Kent DeGroff: “When I image objects, I am interested in seeing what light I can pick up and how well I can process the results … I’m basically referring to the camera exposures in the different colors. Different objects produce light in different regions of the spectrum depending on their nature. The composition of nebulae, for example, varies. They contain gas and dust in varying concentrations and are lit by nearby stars (or not, for dark nebulae) making them glow through ionization or by reflection. A lot of the nebulae are very faint and require long exposures to see … I might have thirty 5-minute exposures with each color filter plus a clear filter for luminescence that all get combined to capture as much light as possible. That would be an integration time of 600 minutes or 10 hours.”

Look to the center of DeGroff’s photograph to find what appears to be the uncanny presence of a battle helmet. The figure is widely identified as Thor’s Helmet. In Norse mythology, Thor is protector of humankind and god of the sky, associated with thunder and lightning. Thor’s Nebula features a very massive central Wolf-Reyet star seen in the center of the helmet structure of gas and dust caused by a stellar wind from that star.

Thor-inspired merchandise, an example of the broad appeal of the myth.

January’s Full Wolf (or Hunger) Moon rises at 4:55 p.m. on Thursday the 28^th as the Sun sets on the opposite horizon at 5:02 p.m. Twilight gathers half an hour later.