Skies Over Crestone: April 2020
The Crestone Eagle • April, 2020
by Kim Malville
Venus continues to be the brilliant jewel in the western sky. It starts the month at nearly its highest possible altitude, gradually getting brighter and brighter throughout the month.
April 1: First quarter moon.
April 3: This is a very special night when Venus collides with the Pleiades. The next time it will happen will be eight years from now. For every eight Earth years, Venus circles the sun almost exactly 13 times. This 8:13 ratio means that Earth and Venus return to nearly the same positions in their orbits in eight-year intervals. Venus visited the Pleiades in April 3, 2012 and will again encounter the Pleiades on April 3, 2028.
April 8: Full moon.
April 14: Last quarter moon.
April 21/22: Lyrid meteor shower. This is a nearly moonless dark night. Each of these meteors is a speck of dust shed by Comet Thatcher which orbits the sun every 415 years. April of every year Earth plows into its debris trail and these particles, about the size of a grain of sand, enter the earth’s atmosphere at a speed over 100,000 miles per hour. This shower was first recorded in 687 BC, making it one of the oldest ever recorded. “On the 4th month in the summer in the year 7 of King Zhuang of Lu the sky is so bright that some fixed stars become invisible because of the meteor shower when stars fell like rain.” Rise early on the morning of April 22 when the shower should peak and the radiant out of which the meteors radiate will be near the zenith before dawn. Bundle up, get a lawn chair and enjoy.
April 23: New moon.
April 26: The moon lies between the horns of Taurus the Bull. Venus is nearby.
Constellation of the Month: Leo the Lion
In the evening between nightfall and 10 pm and face southward. The two brightest stars you will see will be in the constellation of Leo. The brighter star will be Regulus, the Little King, at the bottom of a starry sickle or backward-facing question mark. That sickle forms the mane and shoulder of the crouching lion. To the left of it is Denebola, which is the tail of the lion. Higher up in the sky, near the zenith, is the Little Lion, one of the silliest and least recognizable constellations in the sky. Impress your friends by this bit of obscure sky lore.
There are thirteen stars in Leo that have exoplanets circling them. Astronomers announced the discovery of GJ 436b in 2010, which is 22 times more massive than Earth and has a huge gas cloud streaming away from it for millions of miles. The planet flies over the poles of the star, which is, of course, very different from our own solar system, where the planets’ orbits lied in a plane around the sun’s equator. In 2017 a rocky exoplanet called K2-18b was found, which appears to be orbiting in the so-called goldilocks zone of its red dwarf star, meaning that liquid water could exist on its surface. The planet is about 2.2 times bigger than Earth and may be covered with water, perhaps with an ice shell like Jupiter’s moon Europa.
Beyond Leo there are many more exoplanets in our skies. As of March 1 of this year, there have been 4187 identified exoplanets orbiting stars in the galaxy besides our own sun. Some of those planets are similar to those we’ve read about in science fiction and fantasy literature. Others are more exotic and more dangerous than any fiction writer could have imagined. The first exoplanet was confirmed in 1991. Before that time, less than 30 years ago, it seemed possible that we might be the only planet in our galaxy, perhaps the only planet in the universe, formed by an extremely rare near-collision between two stars. Now we know the galaxy teems with planets. There are, in fact, more planets than stars in the Milky Way. The constellation of Pisces contains the most bizarre exoplanet yet found, named WASP-76 b, an ultra-hot Jupiter that lies about 640 light-years from the sun. WASP-76 b is named for robotic telescopes called the Wide Angle Survey of Planets in Spain and South Africa. The planet circles its host star once every 1.8 Earth days. It is so close to its sun that the planet is tidally locked, always presenting to the star the same face. Temperatures on the dayside reach 4,350°F, hot enough to vaporize metals. The nightside is much cooler, a mere 2,730°F. These are the most extreme climates ever found on a planet, far, far worse than the “hell hole” of Venus. Telescopes have detected a strong signature of iron vapor at the evening border between day and night. But no iron vapor was found in its atmosphere in the morning border on the other side of the planet. The best explanation is that scorching hot winds carry vaporized iron from the dayside to the nightside, where the atmosphere is cool enough for the iron vapor to condense into liquid droplets of pure iron. That rain doesn’t just fall down in a gentle mist. The big temperature disparity between two halves generates winds of great ferocity. The iron in the planet’s dayside air must be hurtling into the nightside like a rain of meteors traveling at about 11,000 mph. The atmosphere on the dayside must be puffier than the nightside and the borders between these two hemispheres might contain dramatic glowing cloudfalls that would rain iron droplets down onto R2D2 or any other tourist fool-hardy enough to visit this weird planet.