FEBRUARY  2010

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703    FEBRUARY 7, 2010:   Sirius and the North Star

The brightest star of the nighttime heavens is…? If your first inclination is to say the North Star or Polaris, let’s just say you’ve just fallen for one of the biggest misconceptions in astronomy. At 9 p.m. this week you can locate the North Star by finding the two upper luminaries of the Big Dipper, now standing handle down, cup up in the NE. These stars are usually called the Pointer Stars, Dubhe (left) and Merak. If you construct an imaginary line between them and move your eyes towards the left, you will pass very close to Polaris. It is situated within a degree of true north and its lack of brightness should be noted. Now turn around and look about a third of the way above the southern horizon to greet Sirius. It is the most dazzling luminary of the night sky and second only to the sun. So why is the North Star held in such reverence? It is very near the pivotal point of the sky, the location where the Earth’s axis intersects the celestial vault. As the Earth rotates or spins in nearly a day, this position remains stationary as the rest of the sky seems to circle around it. Verify this fact by trying an interesting, simple experiment. In a standing position, bend your head back and try to locate the star which you believe to be directly over your head. Make sure that your footing is secure. Slowly begin to rotate (spin) and watch how the heavens start circling around your own personal “North Star.” Your rotating body is acting just like the Earth’s axis. The first time that I had my students perform this little exercise in a planetarium, I had the room completely dark. Twirling around rapidly several times and snapping my head back into the horizontal, I suddenly realized that I had no conception of up and down. Embarrassment followed as I fell. Luckily, Jessie Leayman happened to be sitting in the front row to cushion my fall, preserve my dignity, and who knows, maybe even save my life.

704    FEBRUARY 14, 2010:   Asteroid, Planets, and Moon on Parade

If the weather cooperates, this week has two interesting venues which are examples of why astronomy is the most accessible of all of the sciences. The first is a close encounter between Venus and Jupiter on February 16. The other event happens on the 18 when the asteroid Vesta passes very close to the star Algieba in Leo the Lion. Venus and Jupiter, the third and fourth brightest objects of the heavens, meet for a brief encounter very low in the WSW on Tuesday. The difficulty in viewing the pair will be their close proximity to the horizon at sunset. Southwestern facing vistas will have to be nearly perfect which makes observations from high-rise apartments and hillcrests ideal. Spot Venus once the sun is fully set by scanning the horizon with binoculars immediately to the left of the sundown position. Above and to Venus’s right, and separated by only one lunar diameter, will be Jupiter. Even higher, will be a thin, waxing crescent moon with plenty of earthshine to light its shadowed portions as darkness deepens. Observations on February 14 and 15 will the reveal the moon closer to the pair. On the 14 the slivery moon stands directly above the sun at sunset, while on the following evening, Luna positions herself about 10 degrees above Jupiter. All three twilights will present stunning views of the trio, but February 16 pits Venus closest to Jupiter. Two nights later, in the east at 10 p.m., the second most massive and brightest asteroid of the heavens, Vesta, passes within 1/5 of a lunar diameter from the naked eye star, Algieba, and half of a lunar diameter from 40 Leonis, an easy binocular star from urban locales. Both luminaries help create the mane of Leo the Lion. February 18 finds Algieba, Vesta, and 40 Leonis in a straight line with Vesta considerably closer to Algieba. Use binoculars to see Vesta. An online map is available in the web version of this article. Good observing!

Look for the asteroid Vesta after 9 p.m. on February 18. Vesta will be in the constellation of Leo the Lion. Follow the Pointer Stars of the Big Dipper to the right to find Leo. Vesta will be very near the naked eye star Algieba in the lion’s mane. Leo’s head and mane look like a backwards question mark. Use binoculars and the inset map to peg Vesta’s position precisely. Map created by Gary A. Becker using Software Bisque's, The Sky software...

705    FEBRUARY 21, 2010:   Lunar Phases are Misunderstood

A 1994 film produced by Harvard shows a university professor explaining lunar phases resulting from the interplay of the Earth’s shadow with the moon. He was describing a lunar eclipse where the full moon enters, and then reemerges from the Earth’s shadow. Although the video was about misconceptions, I have a reason for getting so “out of joint” about not understanding lunar phases. During our lives we witness the cyclical phases of the moon hundreds of times. It would seem reasonable that we should know the correct explanation for them. The phases of the moon result from its orbiting of the Earth and our witnessing its day and night cycle. These phases begin when Luna is in the same line of sight as the sun. We say that the phases are brand new and call it a “new moon.” In this orientation at least twice a year the moon can cover or partially block the sun creating a solar eclipse. As the moon orbits around the Earth and its angle from Sol increases, more of its surface becomes visible. The moon is growing or waxing. We first see a horned or thin crescent moon emerge after sundown. The “waxing crescent” thickens until it is half lit, with the reflected sunlight to the right and in the solar direction. The terminator, where the sun would be rising, appears as a perfectly straight line. The moon has now moved through one quarter of its phases, and this is called a “first quarter” moon. On Monday, Feb. 22, the moon reaches first quarter at 7:44 p.m., EST. As the moon-sun angle increases, more sunlight will illuminate its surface, causing Luna to grow into the “waxing gibbous” phase. Gibbous means to be convex or swelling. The moon bulges on both sides, but its light is still to the right. Finally, Luna is opposite to the sun as a “full moon.” This occurs Sunday, Feb. 28. We will have witnessed the moon phase cycle from night into day. We’ll complete the phases of the moon next week.

706    FEBRUARY 28, 2010:   Misunderstood Lunar Phases

The moon is one of the most common and yet one of the most misunderstood objects in the sky. It was used by ancient cultures to formulate many of the first calendars because it was an easy view and cycled through its phases in the short period of 30 days (29.54 days on average). We get our word “month” from the moon’s phase period. Yet when asked to explain the causes of the phases, the educated and uneducated alike, render theories that usually involve the moon passing in and out of the Earth’s shadow. In other words we get the basis of lunar phases mixed up with lunar eclipses, where the full moon actually does pass through Earth’s shadow. The explanation of the phases is so simple that we usually miss the point completely. As the moon orbits the Earth, changing its position in the sky night after night, we are simply witnessing the hemisphere that is perpetually facing us moving through a day and night cycle. If you’re looking at Luna on Sunday, February 28, the moon will be at opposition (opposite) to the sun and full in the sky. A casual glance one or two days before or after the full moon will usually elicit a full phase response. This extended period for the full moon is probably the origin for the misconception that when the moon is full, human behavior becomes more eccentric. Nurses claim there are even more hospital births. During a five or six day period, something weird is bound to happen; but if incidences of crime or births are tallied for just the night of the full moon, there is no statistical increase over any other randomly picked evening in the lunar cycle. Watch as the moon wanes over the next two weeks, decreasing in brightness, first as a waning gibbous moon through March 6. The next day, Luna is at last quarter, half on—half off, light to the left. Afterward, Luna wanes as a crescent or horned moon. Finally, on March 15 at 5:03 p.m., a new lunar cycle begins again.