Venus visits Alnath, a star with dual citizenship

SkyCaramba weekly astronomy blog for the week ending May 12, 2012

Venus passes very close to a star that’s actually part of two constellations. Alnath (also El Nath or Elnath) looks like part of Auriga. In our modern constellation map, we find it slightly inside Taurus. Some constellation art shows it to be the end of a very long horn from Taurus. Alnath is Arabic for “the butting one”. 

It’s easy to spot Venus this week. Look to the west after sunset and the bright dazzling object you see is Venus. A few other stars nearby are those of Auriga. On the 6th, it will be as close at 0.8° from Alnath. 

Venus is so bright because of how close it is to the sun and what’s in its atmosphere. The light reaching Venus is rather strong at such close range. And the clouds in the planet’s atmosphere are very reflective. They’re made of sulfuric acid that starts eating away at space probes the moment they enter the planet’s air. 

Auriga is a Latin word for charioteer. The constellation’s stars form the outline of a chariot driver’s helmet. However, most constellation art shows this constellation as the chariot driver himself. To the ancient Greeks, either Hephaestus or his son Erechtheus, invented the chariot as a way to get around because neither could walk. Whoever’s driving, he’s often shown carrying a goat over the shoulder represented by the bright star Capella which is opposite Alnath. 

Capella is famed for being the goat Zeus nursed from. He accidentally broke off one of the horns and turned it into a sort of magic wand for producing plenty of food. The story is alluded to in the word cornucopia, a Latin construction meaning “horn of plenty”. The star Capella is easy to identify when you spot a tall isosceles triangle of three stars near it. Those are sometimes represented as three baby goats. 

Venus was at its brightest on May 1. As it rounds the sun, Venus is getting closer to Earth. But as it does, it’s turning its dark side to us. It started the month looking in telescope views slightly gibbous like the moon just past first quarter. By the 10th, it will be a fat crescent that keeps getting thinner from night to night. Don’t worry. Even when very little of Venus is illuminated, it’s plenty bright. You’ll actually lose sight of the planet toward the end of May as it heads into conjunction with the sun. Next month’s conjunction will be special. From some parts of Earth, people will be able to see Venus pass right in front of the sun’s disk. Take care of your eyes. Don’t look at the sun directly without proper protection. 

As you look at Venus this week, think of how things would have looked in 1875. Venus would have been elsewhere, but Alnath would have been right on the line between Auriga and Taurus. That’s why we can call it a dual citizen, although astronomers prefer the term linking star.