Arcturus is one of three stars noticeable for flashing in colors at this time of year. You should be able to see it at dusk or nightfall. Once it gets good and dark, and you live at mid-to-far latitudes in the Northern Hemisphere, you can verify that this star is Arcturus by using the Big Dipper asterism. The arc of the Big Dipper handle extended outward always points to Arcturus.
Every year at this time, we get questions about three different stars that are flashing different colors. One is Capella in the constellation Auriga the Charioteer, which is now in the northeast in mid-evening. One is Sirius in the constellation Canis Major the Greater Dog, which is now in the south before dawn.
And the third is shining in the west to northwest after sunset: Arcturus in the constellation Bootes the Herdsman. It’s flashing colors for the same reason Sirius and Capella are . . . because all three of these stars are bright and, at this time of year, noticeably low in the sky. When you see an object low in the sky, you’re seeing it through a greater thickness of atmosphere than when it’s overhead. The atmosphere refracts or splits the stars’ light to cause these stars to flash in the colors of the rainbow.
At mid-northern latitudes, scintillating Arcturus adorns the western evening sky all through October.
Also this evening, look for the planet Saturn plus the star Antares in your southwest sky as darkness falls.
Bottom line: On October evenings, look for the brilliant star Arcturus in the western sky, flashing in colors. The Big Dipper’s handle points to this yellow-orange star.