From the December 2021 issue

Ask Astro: Is Sirius part of the Milky Way? Does it have any planets?

By | Published: January 5, 2022 | Last updated on May 18, 2023
Japanese amateur astronomer Akira Fujii captured this close-up shot of the sky’s brightest star. The Sirius star system contains two stars, but so far no identified planets.
Akira Fujii

Is Sirius part of the Milky Way? Does it have any known planets?

Thomas Steiner 

Greendale, Wisconsin 

Sirius is the brightest star in the Northern Hemisphere. In order to see a pointlike star with your naked eye, it must be relatively close to us; this means that all the stars you can see in the night sky are within the Milky Way Galaxy. Resolving individual stars in other nearby galaxies, such as Andromeda in the Northern Hemisphere or the Large and Small Magellanic Clouds in the Southern Hemisphere, requires professional equipment like the Hubble Space Telescope.

Sirius is about 8.6 light-years from Earth. There are two identified stars in the Sirius star system, a main sequence spectral type A star and a faint white dwarf, designated Sirius A and B, respectively. No planets have been identified in the system so far. Combining Hubble observations with historical measurements dating back to the 19th century, researchers have ruled out the possibility of any brown dwarfs or any exoplanets larger than 15 times the mass of Jupiter. However, looking at our own solar system’s plethora of smaller planets, it’s not a stretch to imagine that there could be a considerable number of exoplanets evading detection in this system.

Caitlyn Buongiorno 

Associate Editor