Venus, Jupiter and Brightness / Magnitude

Welcome back to another year of astronomy tips and news from the Urban Astronomer. I enjoy the opportunity to share astronomy with the Waldorf community and am glad to appear in the school newsletter from time to time. Throughout the year I'll talk about the changes in the night sky from season to season, share some insights about constellations and other celestial objects, provide information about special events such as eclipses and meteor showers, and of course highlight the changing positions of the planets and the beautiful arrangements of the moon, planets and stars that fill our skies throughout the year.

As we move toward Fall, the days are rapidly getting shorter and you might find yourself in the dark in the morning. Sunrise is at approximately 6:50 am which means if you are an early riser, you will have noticed brilliant Venus which is increasing in brightness and is rising due east more than two hours before the Sun. Just how bright is Venus? Astronomers use a curious system to measure the brightness of stars and planets. The system is called the "magnitude" system and it work the opposite of what you might expect, with lower numbers (and negative numbers) being brighter than higher numbers. For example, the north star (Polaris) is magnitude 2, but a brighter star directly overhead right now is Vega and its magnitude is 0. Venus is even brighter still, blazing at magnitude -4, almost the brightest it gets all year.

In the evening you can see Jupiter which dominates the southwest sky after sunset. Using the same brightness scale, Jupiter shines at magnitude -2. You can compare this to the red giant star Antares which is nearby Jupiter and although impressive at magnitude 1, seems faint compared to bright Jupiter. In the coming weeks you will notice Jupiter getting lower and lower in southwest sky, eventually fading into the sunset in a few months. Next week on Monday and Tuesday the waxing Moon will have a close encounter with Jupiter so if weather permits, enjoy the show anytime after sunset which next week is at approximately 7:15 pm.