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Last updateWed, 27 Aug 2014 10am

Astronomy

March 2015 at dusk: Early in the month, the four brightest “stars,” in order of brilliance, are: Venus, in the west; Jupiter, in the eastern sky; Sirius, the “Dog Star,” 40 degrees up in the south as seen from the Coachella Valley; and Canopus, less than 4 degrees up when it passes due south about 21 minutes before Sirius does.

From the Coachella Valley, you must choose your site carefully to see Canopus, or mountains might block your view. From my abode in Palm Springs, I see Canopus blink out when it goes behind a mountainside several minutes before it reaches its high point.

From Palm Springs and Desert Hot Springs, Canopus passes due south only 4 degrees up in a dark sky at 7:32 p.m. on March 1, and then four minutes earlier each day, to 7:08 p.m. on March 7, and suddenly 8:04 p.m. on Sunday, March 8—an hour later than you might expect, until you recall that you’ve just reset your clock to daylight saving time. By March 11 or 12, the star reaches its high point only about an hour after sunset. Within a few more days, as the star’s “transit time” backs closer to the time of sunset, the sky will become too bright to catch Canopus at its high point.

Sounds of nature enrich the stargazing experience. In Palm Springs, we’ve been hearing frogs in nearby Tahquitz Creek on warmer nights since December.

Other features of the early evening: A telescope reveals Venus now in gibbous phase,and up to four of Jupiter’s moons discovered by Galileo in 1610. Mars, now on the far side of its orbit, doesn’t reveal much telescopically, but it’s visible to the naked eye and binoculars, sinking lower in twilight, 4 degrees to 17 degrees below Venus.

Orion’s three-star belt (not bright enough to be shown on our twilight chart) lies midway between red Betelgeuse and blue Rigel. The belt points the way leftward toward Sirius, and the opposite way toward Aldebaran, eye of Taurus, the Bull, and beyond to the Pleiades or “Seven Sisters” star cluster (also not plotted, but beautiful in binoculars). The huge “Winter Hexagon”—in counterclockwise order, Sirius, Rigel, Aldebaran, Capella, Pollux, Castor (not shown), Procyon and back to Sirius, with Betelgeuse inside—contains seven of the 21 stellar objects of first magnitude or brighter (16 stars and five planets) ever visible from Southern California. Their constellations include a bull backing away from a charging hunter and his two canine followers, a pair of twins and a chariot driver with mother goat and three kids on his shoulder.

Following this menagerie is bright Jupiter, itself followed by Leo, the Lion, with the star Regulus marking his heart.

By March’s end, Arcturus, the “Bear Guardian” star, pops up above the east-northeast horizon before mid-twilight. Use this memory aid: “Follow the arc (curve of the bear’s tail or handle of the Big Dipper) to Arcturus.”

The moon can be easily spotted daily at evening mid-twilight (about 40 minutes after sunset) March 1-5 and March 21-April 4. At dusk on Monday, March 2, the fat gibbous moon is well up in the eastern sky, 5 to 6 degrees to the north (upper left) of Jupiter. Now through July, the moon will pass Jupiter in the evening sky every 27 or 28 days. The interval is shorter than the moon’s cycle of phases, 29.5 days, so each time it overtakes Jupiter, the moon will appear progressively less full.

On March 4, the nearly full moon will rise 35 to 40 minutes before sunset, and on March 5, the moon, just past full, rises shortly after sunset. In the following days, moonrise occurs nearly an hour later each night, making it more convenient to switch your moon-watching time to predawn.

March 2015 at dawn: The brightest objects in morning twilight, in order of brilliance, are: Arcturus, high in the west-southwest to west; and Vega, high in the northeast. Early in the month, Mercury, low in the east-southeast, closely matches or slightly outshines Arcturus, but it sinks into bright twilight after midmonth. Saturn, steady in the south to southwest, is next in brightness in the morning sky.

In morning twilight on Thursday, March 5, the full moon is low in the west, with Regulus setting 4 to 5 degrees to its lower right. On March 8 and 9, the waning gibbous moon appears in the southwest near Spica. On Thursday, March 12, Saturn appears within 3 degrees to the lower right of the moon in the south, while the reddish twinkling star Antares appears 8 to 9 degrees to their lower left. On Friday, March 13, the moon is close to half full and essentially at last quarter phase, 90 degrees west of the sun and 14 to 16 degrees left (east) of Antares and Saturn. The last easy morning view of the waning moon will come on Wednesday, March 18.

The moon returns to the evening on Saturday, March 21, at dusk, when the 1.7-day-old waxing crescent will be very easy to spot. Mars will be 2 degrees to its lower right. For a few more evenings, look for beautiful earthshine, from sunlight reflected by Earth onto the moon’s dark (non-sunlit) side. Watch the crescent thicken daily as it moves farther from the sun on each successive evening.

Mark your calendars: On Friday evening, April 3, the nearly full moon will rise 4 to 5 degrees south of due east about 26 minutes before sunset. About 13 minutes before sunset, the sun and moon can be viewed simultaneously, in opposite directions, each about 2 degrees above unobstructed horizons. About an hour after sunset, look for Spica 13 degrees below the moon—and then atotal lunar eclipsewill happen early Saturday morning, April 4. More on this next month and at CVIndependent.com.

Using a rectified Earth globe outdoors in sunlight: If it is set up properly outdoors in sunlight, an Earth globe can reveal the location of the sunlit area on the actual Earth at the moment you are viewing the globe.

Here are directions for setting it up. It would be most helpful if you could use a globe with a dull finish:

1. Find your location. Use longitude and latitude if necessary.

2. Place the globe so that your location is at the top of the globe, i.e., at the highest point on the sphere, at the point of tangency of a horizontal plane tangent to the top of the globe.

3. Rotate the globe about a vertical axis until the directions north, east, south and west at your chosen location on the surface of the globe match the directions of your actual surroundings. During this step, make sure your location remains on the top of the globe.

4. You have now “rectified the globe,” and its orientation in space matches that of the actual Earth. The rotation axis of the globe points very nearly toward the North Star, Polaris, as does the axis of rotation of the actual Earth. Any time you view the globe, its sunlit area matches the sunlight area on the actual Earth.

Examine the globe to discover in what parts of the world the sun is rising, and where it is setting at the time you view the globe. To help solve this problem, watch the globe for several minutes or check it after an hour to detect changes in the location of the lighted area.

On March 20, the date of the spring equinox, the North and South poles should both be on the terminator, or dividing line between the day and night sides of Earth. The sun is directly overhead on the equator. As the Earth rotates on its axis on that date, each location will have days and nights each 12 hours long.

Before March 20, the sunlit area extends beyond the South Pole, and falls short of the North Pole. It is daytime at the South Pole and nighttime (perhaps twilight, depending on the date) at the North Pole. After March 20, the sunlit area falls short of the South Pole, and extends beyond the North Pole, so it is nighttime (perhaps twilight) at the South Pole and daytime at the North Pole.

The “half moon” as a reviewer or predictor of the seasons: The following statement is true throughout the year: the last quarter moon, or half moon at sunrise, reviews the sun’s location of three months ago, and the first quarter moon, or half moon at sunset, predicts the sun’s location three months in the future.

These facts are especially well demonstrated in March: The morning half moon at sunrise on March 13 is low in the southern sky, in Ophiuchus, not far from the southernmost part of the zodiac in Sagittarius where the sun appeared in December, near the start of winter.

The evening half moon at sunset nearly two weeks later on March 26 is high in the southern sky, in the club of Orion, not far from the northernmost part of the zodiac near the Taurus-Gemini boundary where the Sun will appear in June, near the start of summer.

You can construct models of the solar system to explain the above facts. Essentials to include in the model are an Earth rotating about its tilted axis while revolving about the sun, and the moon revolving about the Earth in approximately the same plane. All three motions are counterclockwise as seen from “above” or north of the solar system. Placards with names of the 13 zodiac constellations can also be properly arranged around the model, as on the planet orbit charts available online at www.abramsplanetarium.org/msta.

Observing challenge: Opposing crescents on consecutive days, March 19 and 20: Given perfect skies and no mountains blocking the view, use binoculars or a telescope to try to see a very thin waning crescent moon on Thursday, March 19, 25 minutes before sunrise, 1-2 degrees up and 5 degrees south of due east. From Palm Springs, the moon is then only 20.2 hours before new.

On the next day, Friday, March 20, in the evening 25 minutes after sunset, use binoculars to try for an even thinner, waxing crescent, 2-3 degrees up and 2 degrees north of due west. From Palm Springs, the moon is then 16.8 hours after new.

Robert C. Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys providing skywatching opportunities for school children in and around Palm Springs.

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