A full Moon, the spring triangle, and other bright, beautiful things to look for in the sky this week.
By Michael E. Bakich
Friday, March 10
Around 6 p.m. EST, Leo the Lion’s brightest star, Regulus, lies only 0.8° north of the Moon. In fact, observers with clear skies located in southeast South America, South Georgia, Queen Maud Land, and the southern tip of South Africa will see the Moon pass in front of Regulus. Astronomers call such events occultations. By carefully observing many of them, researchers can more accurately map the variations (caused by mountains and valleys) at the lunar edge.
Saturday, March 11
Head out tonight sometime after 10 p.m. to see a naked-eye asterism called the Spring Triangle. This giant geometrical figure is visible in the spring all night long from any location in the Northern Hemisphere. Three dazzling stars mark this asterism. The brightest is Arcturus (Alpha Boötis), which shines at magnitude –0.04 near the bottom of Boötes the Herdsman. Orange Arcturus is the fourth-brightest nighttime star overall and the brightest north of the celestial equator. Next in brightness is Spica (Alpha Virginis), the luminary of Virgo the Maiden. Spica is the very definition of a 1st-magnitude star, but its brightness isn’t constant. Its apparent magnitude varies between 0.92 and 1.04 over a period of just more than 4 days. The third Spring Triangle star is Denebola (Beta Leonis), the star that marks the tail of Leo the Lion. And although Denebola, at magnitude 2.1, is the sky’s 59th-brightest star, it’s only 36 percent as bright as Spica, and it emits just 14 percent the light output of Arcturus.
Sunday, March 12
Daylight Saving Time begins this morning. Be sure to spring forward one hour.
Full Moon occurs at 10:54 a.m. EST. The glowing orb stands in the far-southern part of Leo the Lion, between the constellations Virgo to the east and Sextans to the west. This lunar phase is the least interesting to observers because sunlight falls straight down on the Moon from our perspective, which minimizes shadow detail. So this might be a good night to observe the Moon illusion — the Full Moon appears larger when it’s near the horizon than when it stands high in the sky. But its size doesn’t change, and you can prove it with a single sheet of paper. Go out just after sunset and find the Moon low in the east. Roll the paper into a tube and change the tube’s diameter until the Moon just fills the field of view when you look through it. Tape the tube so its size doesn’t change. Then, head indoors and go back outside a few hours later when the Moon is high. Look through the tube again. The fact that the Moon will be the same size still amazes even seasoned observers. The best explanation for this illusion seems to be that when the Moon lies near the horizon, our brain compares its size with foreground objects, which don’t appear near the Moon when it’s high in the sky.