• An Australian visitor wrote, I seek to find out what speed our sun is traveling at and also how many years it takes to circumnavigate the galaxy.
• Our Milky Way galaxy is a collection of several hundred billion stars. It has an estimated diameter of 100,000 light-years. Our sun does indeed circumnavigate the Milky Way galaxy. In space, everything moves. There are various

estimates for the speed the sun travels through the galaxy, but its speed is about 140 miles per second.
• Likewise, there are many estimates for the length of time it takes the sun to complete one circuit of the galaxy, but a typical estimate is about 230 million years.
• That period of time, by the way, is known as a cosmic year. It so happens that astronomers know which star the sun is moving toward in its journey around the galaxy. At this time of year from mid-northern latitudes, this star appears over the northwest horizon at dusk but sets shortly thereafter. It also appears low in the northeast sky at and before dawn. It's one of the loveliest stars you'll ever see, Vega in the constellation Lyra the Harp.
• By the way, Vega resides almost exactly opposite of Sirius, the brightest star in the nighttime sky. When Sirius sits low in the southeast, as it does at dusk or early evening at this time of year, Vega lurks low in the northwest and sets shortly thereafter. But much later tonight (as seen from mid-northern latitudes) Sirius swings low in the southwest sky by around 2 to 3 a.m. Also, as viewed from mid-northern latitudes, the dazzling planet Jupiter is close to setting in the west-northwest sky. This is when to look for Vega to reappear in the northeast sky.
• Our sun's direction of motion (and thus our Earth's corresponding motion) toward Vega has a special name. It's called the apex of the sun's way. Vega - the solar apex star - can be found in the eastern sky during the dawn and predawn hours throughout the winter season.
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