Astronomy Day takes place on October 12, 2013. The photo at the top of this post is facing eastward before dawn this morning, on this Astronomy Day. The bright object above the tree is Jupiter. You can also see the constellation Orion at the lower right of this photo, which is by EarthSky Facebook friend Stacy Oliver Bryant. Thanks, Stacy! On this special day, astronomy enthusiasts reach out to the public to share the wonders of the universe. Follow the links below to learn about some night sky objects and events you can see on or around this Astronomy Day, October 12, 2013.
What is Astronomy Day? Astronomy Day comes twice a year, on a Saturday. Earlier in the year, the event happens sometime between mid-April and mid-May. Later in the year, Astronomy Day comes somewhere between mid-September and mid-October. Astronomy Day is a movable feast, falling on the Saturday that most closely coincides with the first quarter moon. On this date, you might find an astronomy club in your area that’s hosting a star party, or other event. Check out what events may be taking place at an observatory or astronomy club near you.
Bright object in the west after sunset is planet Venus. From around the world now, the brightest object up after sunset is the planet Venus. Venus was near the moon earlier this month, but now the moon has waxed larger and moved to a different part of the sky. But if you look closely, you’ll easily see a bright star near Venus. This star is Antares, the red-colored Heart of the Scorpion in the constellation Scorpius. Venus and Antares will be drawing closer on the sky’s dome in the coming days. They will be closest around October 16. Watch for them!
Moon is in a waxing gibbous phase. A waxing gibbous moon appears high in the east at sunset. It’s more than half-lighted, but less than full. Last quarter moon was yesterday, so the moon you’ll see on this Astronomy Day, October 12, is just barely a waxing gibbous. People sometimes see a waxing gibbous moon in the afternoon, shortly after moonrise, while it’s ascending in the east as the sun is descending in the west. It’s possible to see a waxing gibbous moon in the daytime because, at this phase of the moon, a significant fraction of the moon’s day side is facing our way. Read more about the waxing gibbous moon.
Planet Jupiter rises middle of night, highest before dawn. Jupiter is at west quadrature – 90o west of the sun – today, October 12. That means Jupiter is half a sky’s dome away from the sun in our sky. In other words, it’s rising in the east around midnight and highest in the sky before dawn.
At quadrature, as now, the shadows of Jupiter and its four major moons – as seen from Earth – slant a maximum of 12o westward of the moons and Jupiter. As seen from Earth, Jupiter’s four major moons swing in front of Jupiter going from east-to-west, and sweep behind Jupiter going from west-to-east.
What this means is that the shadows of Jupiter’s moons transit – cross – Jupiter’s surface before the moons themselves do. As the moons circle behind Jupiter, the moons move into Jupiter’s long shadow before they pass behind Jupiter.
Perhaps an observatory or an astronomy club celebrating Astronomy Day can show you Jupiter’s moons through a telescope tonight. But you have to be a night owl or an early bird to witness the attraction, because, remember, Jupiter doesn’t rise until around midnight local time.
Bottom line: Happy Astronomy Day 2013. Maybe you can find a local astronomy club or nature center in your area that’s hosting a star party or other night sky event today or tonight. If not, this post offers some easy-to-look-for objects and events in the night sky.