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(Times are for San Francisco, CA, and will vary slightly for other locations.)
On April 8, as every 26 months, Earth and the slower-moving Mars line up on the same side of the Sun in what astronomers call “opposition,” with Earth between Mars and the Sun. At this time, Earth and Mars are closest-together, and as seen from Earth, Mars appears brighter and larger than usual—though not so large that its disk can be seen with the unaided eye (it’s still about 57 million miles away). This is when astronomers find it optimal to observe features on Mars, including its ice caps and dark patches. An early pioneer in telescopic Mars observations was Percival Lowell, a wealthy Bostonian and avid astronomy enthusiast who financed the construction of the famous Arizona observatory that bears his name. He was an ardent proponent of the supposed and now-discredited Martian “canals” but he also led the search for a theorized ninth planet beyond Neptune. Although he himself didn’t discover “Planet X,” it was at his Arizona observatory where Clyde Tombaugh finally found what would—at least for 76 years—be known as a planet, the little world called Pluto.
Mars-bound spacecraft are usually launched a few months before opposition to take advantage of the closing distance between the two planets and minimize travel time. Currently headed for the Red Planet are NASA’s Mars Atmosphere and Volatile EvolutioN orbiter (MAVEN), launched on November 18, 2013, and India’s Mars Orbiter Mission (MOM), launched on November 5, 2013. Neither carries a lander, and both are expected to enter orbit around Mars in September. For more information, visit http://lasp.colorado.edu/home/maven/ and http://www.isro.org/pslv-c25/mission.aspx.
The following asteroids will make their closest approaches to Earth in April, though “close” is a relative term – none will be close enough to be of any concern whatsoever: 12258 (writer) Oscarwilde, 6701 (pop artist Andy) Warhol, 128036 (tennis star) Rafaelnadal, 19367 (rock group) Pink Floyd, 6600 (keyboard arrangement) Qwerty, 17627 (nursery rhyme character) Humptydumpty, 2991 Bilbo (Baggins, of Tolkein’s “The Hobbit”), 17078 (actor Peter) Sellers, 1862 Apollo, 128523 Johnmuir, 163800 Richardnorton, 12284 (science fiction author Frederik) Pohl, 17744 (actress) Jodiefoster, 9954 (dinosaur) Brachiosaurus, 17059 Elvis (Presley, entertainer), 35350 (guitar maker) Lespaul, and 4321 Zero (Mostel, actor/comedian – also the completion of a countdown, giving this asteroid’s name a clever double-meaning).
On April 12, 1961, the Soviet Union launched Vostok 1, carrying cosmonaut Yuri Gagarin into orbit and back, making him the first human to fly in outer space. Fifty-three years later, this date has come to be known as “Yuri’s Night,” a worldwide commemoration of human spaceflight in art, science, and culture in which multiple venues are holding events to celebrate the past, present, and future of space travel. Visit http://yurisnight.net/#/home for more information.
Skywatchers will be treated to a total lunar eclipse on the night of April 14/early morning of the 15th as the Full Moon glides through Earth's shadow. This usually causes our satellite to turn a deep, rusty reddish color, because Earth’s atmosphere refracts, or bends, the Sun’s light that passes through it, filling in the otherwise dark shadow with the color of all the sunrises and sunsets happening at that moment. As the Moon passes through the umbra (the dark, inner portion of Earth’s shadow), this red light slowly creeps across its face, the intensity of the color depending on how clear the air is along the ring of atmosphere through which the sunlight is shining. This event will be visible throughout the United States, starting at 10:58 p.m. PDT, with totality (when the Moon is completely immersed in the umbral shadow) lasting from 12:06 a.m. PDT until 1:24 a.m. PDT. As the Moon slowly exits the shadow, the partial eclipse ends at 2:33 a.m. PDT.
Aside from Mars, two of the largest objects in the asteroid belt come into opposition in April: 4 Vesta on the 12th and 1 Ceres on the 14th—both seen against the stars of Virgo the Maiden. Vesta, the smaller of the two, is 326 miles across and is the brightest asteroid visible from Earth due to a combination of its size, distance, and reflectivity that makes it barely visible to the unaided eye. It was discovered in 1802 and was visited by NASA’s ion-powered Dawn spacecraft (http://dawn.jpl.nasa.gov/), which orbited it for a year starting in July 2011. Then, Dawn rocketed off for a rendezvous with larger but more distant Ceres, an encounter which is expected to occur in March 2015. As its numerical designation indicates, Ceres was, in 1801, the first asteroid to have been discovered. At 590 miles across, it is the largest object between Mars and Jupiter. Initially labeled “planets” when they were discovered, Ceres and Vesta were later reclassified as “minor planets/asteroids” when more and more similar objects were discovered in the asteroid belt. In 2006, Ceres was reclassified yet again as a “dwarf planet” along with the Kuiper Belt objects Pluto, Eris, Haumea, and Makemake. Thus elevated in status by the same redefinition that demoted Pluto from planethood, Ceres is the only dwarf planet located in the inner solar system. The other four bodies reside beyond the orbit of Neptune and thus are also labeled “plutoids” (meaning, ironically, that although Pluto lost its planetary status, its name became a whole new category of solar system object). Over the next few months, Ceres and Vesta will be moving closer together, appearing only a fifth of a degree apart on July 4.
On April 22, the annual Lyrid meteor shower peaks. Typically active from April 16–25, this shower is caused by Earth passing through the dust-trail of Comet C/1861 G1 Thatcher, causing about 15–20 meteors per hour radiating from Lyra the Harp. This is the oldest shower currently known, with Chinese records dating back to 687 BC. The parent body, Comet Thatcher, has been observed only once, in 1861. This year, the narrow peak is coincident with a last quarter Moon that rises around midnight, so unfortunately, moonlight may obscure the view somewhat.
The annual Eta Aquarid meteor shower peaks on May 5 and is one of two showers caused by dust particles from Halley’s Comet burning up as they enter Earth’s atmosphere. While most other known comets have paths that intersects Earth’s orbit only once, Halley’s path does so at two points—giving rise to the Eta Aquarid and Orionid meteor showers of May and October, respectively, as our planet sweeps up the particles of dust left scattered along the comet’s trajectory. The Eta Aquarids usually last from April 21 through about May 12, and during the May 5/6 peak, observers might see 10–20 meteors per hour. As the name suggests, meteors from this shower appear to radiate from the vicinity of the constellation Aquarius the Water-Carrier, which rises a mere three hours before the Sun. Fortunately, the first quarter Moon will have set by midnight, leaving skywatchers with a dark pre-dawn viewing opportunity.
May 10 is Astronomy Day, founded in 1973 by the Amateur Astronomers of Northern California, usually taking place on a Saturday in either April or May nearest the first quarter Moon. Immediately popular, Astronomy Day has become a national observance, giving amateur and professional astronomers alike the opportunity to share their love of stargazing with the public through presentations, displays, and activities at planetariums, observatories, science centers, and street corners around the country. If the sky is clear, telescopes are set up for free glimpses of this night’s targets: the Moon, the ringed planet Saturn, and the constellations. There’s more information at http://www.astroleague.org/al/astroday/astrodayform.html.
When the city of Chicago turned 100 years old, the occasion was celebrated with the “Century of Progress” Exposition, also known as the Chicago World’s Fair. On opening night, May 27, 1933, lights across the fairgrounds were switched on in a novel way. Using telescopes, the light of the bright star Arcturus, in the constellation Boötes the Herdsman, was directed onto photocells (converting the light to electricity) at four observatories which simultaneously telegraphed signals to Chicago, activating the lights. At the time, Arcturus was thought to be 40 light years away, so the thinking was that the starlight detected in 1933 would actually have left that star 40 years earlier, coincidentally during the World’s Columbian Exposition, which also happens to have been held in Chicago, in 1893. Today, astronomers say the distance to Arcturus is 37 light years, but it was a clever idea to use the star’s distance to link the two events in time. Arcturus can be seen in the Spring sky and is easily found by following the arc of the Big Dipper’s handle to it. Since it’s the brightest star in the northern half of the sky, it’s easy to spot. Just remember the phrase “Follow the arc to Arcturus.”
The following asteroids make their closest (but still very distant) approaches to Earth in May: 6336 (extinct bird) Dodo, 2041 (Arthurian knight) Lancelot, 12542 (‘60s tennis star Rod) Laver, 25399 (writer Kurt) Vonnegut, 5891 (baseball player Lou) Gehrig, 184784 (‘50s pinup model) Bettiepage, 166614 Zsazsa (Gabor, ‘40s actress) 9941 (dinosaur) Iguanodon, 4122 (sportscar maker Enzo) Ferrari, 125071 (“Dracula” actor Bela) Lugosi, 4487 (Native American historical figure) Pocahontas*, 716 (city of) Berkeley, 9880 (Jurassic dinosaur) Stegosaurus, 9340 (actor) Williamholden, 21811 (fantasy writer Edgar Rice) Burroughs, and 18932 (English folk hero) Robinhood.
*Fascinating factoid: remember Percival Lowell from way back up in the April 8/Mars item? He was a direct descendant of Pocahontas, after whom asteroid 4487 was named.
June 21 is when the north pole of Earth is tipped most toward the Sun, making it the Summer solstice in the northern hemisphere. On the other hand, the south pole is tipped away from the Sun, so it’s the Winter solstice in the southern hemisphere. On this day, the Sun rises and sets at its northernmost points and makes its longest, highest arc across the sky, resulting in the Sun being above the horizon for the longest period of the year. In fact, at the north pole (and points north of the Arctic Circle, or 66.5°), the Sun is above the horizon for 24 hours. At the south pole (and points south of the Antarctic Circle, or -66.5°) the Sun never rises above the horizon. On the Tropic of Cancer—23.5° N latitude—the Sun is directly overhead at solar noon.
June’s interestingly-named asteroids making their closest approaches to Earth: 4017 Disneya (after cartoonist Walt Disney), 17942 (“Alice in Wonderland” character) Whiterabbit, 9621 Michaelpalin (of Monty Python), 9622 Terryjones (of Monty Python), 9620 Ericidle (of Monty Python), 6433 (singer) Enya, 5062 (bandleader) Glennmiller, 6827 (endangered marsupial) Wombat, and 15495 Bogie (after actor Humphrey Bogart).