Putting together a profile of a star is hard, even for one of the brightest stars in the sky. It takes careful observations and good models of how stars work. And as technology and theory improve, so does the profile.
As an example of that process, consider Canopus, the second-brightest star in the night sky. At this time of year, it just peeks above the southern horizon in early evening from the southern third of the United States. It’s well below Sirius, the night’s brightest star.
One key is a star’s distance. Until about 25 years ago, estimates of the distance to Canopus varied by hundreds of light-years. But a space telescope locked it down: 310 light-years.
Knowing the distance reveals the star’s true brightness. That’s combined with other details, then plugged into models of how stars evolve. That provides a good estimate of the star’s age, its stage in life, and more.
One other key detail is the star’s size, which is hard to measure — Earth’s atmosphere blurs the starlight into a fuzzy blob.
In a recent study, though, astronomers got the best measurement of Canopus’s diameter to date — about 74 times the Sun’s diameter. Adding that to the other details refined the star’s profile. It varied a little depending on which model was used. But the models agreed that Canopus is almost 10 times the mass of the Sun, and anywhere from 24 million to 34 million years old.
Of course, that could change — with more hard work.
Script by Damond Benningfield