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Use Sirius to imagine sun’s path through Milky Way

If you’re in the Northern Hemisphere now, you can use the brilliant star Sirius – and the star Vega – to imagine the direction our sun and solar system are traveling through space. The sun in its orbit is traveling away from Sirius and toward the star Vega. Although we couldn’t fit them both on one chart, Vega shines over your northwestern horizon, opposite Sirius, at dusk/nightfall at this time of year. Vega sets at early evening while Sirius stays out until the wee hours of the morning.

So if you stand outside at dusk or nightfall with your back to Sirius – facing northwest – you’ll be facing the direction our solar system moves through the Milky Way galaxy. Cool, huh?

Tonight’s chart, and the photo below, both can help you be sure you’re seeing Sirius. Both show the east-southeastern sky not long after the sky gets dark, as viewed from mid-northern latitudes. The brightest star of nighttime – Sirius – shows up close to the horizon in early evening, rising upward as evening deepens into night. Sirius is found by drawing a line through the three stars of Orion’s Belt.

When an overwhelmingly bright star like Sirius hovers near the horizon, it doesn’t just twinkle. It scintillates: sparkles in red and blue.

By the way, the direction to the star Vega – the general direction toward which our sun is traveling through space – is called the solar apex or sometimes the apex of the sun’s way.

View larger. | No matter where you are on Earth, the three stars of Orion’s Belt always point to Sirius on our sky’s dome. Here they are rising over Madeline Island in Lake Superior (USA) in January, 2013. EarthSky Facebook friend Jim Peacock captured this scene. Thank you, Jim!

Bottom line: Look for the star Sirius in the constellation Canis Major at nightfall tonight. It’s easy to find because it’s so bright – brightest star in the sky. Once you find it, turn around so that your back is to this bright star. You’ll be facing into the sun’s path through the Milky Way!

How long does it take our sun to orbit the Milky Way’s center?

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