StarWatch for the greater Lehigh Valley

MARCH  2016


Print Large Sky Charts For 9 p.m. EDT:   NORTH | EAST | SOUTH | WEST | ZENITH

[Moon Phases]

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Current Geomagnetic Field:    


1020    MARCH 6, 2016:   Seeing the Young Moon
One aspect of the evening sky in the spring is that the ecliptic, the Earthís orbital plane projected into space, is tilted at a steep angle (about 70 degrees) to the western horizon. Since the moon orbits near to the ecliptic, this affords an opportunity for the fast moving moon to be seen as a razor thin crescent a day or so after its new phase. The conditions are right for a series of these types of observations this week if weather conditions cooperate. The moon is new, passing the sun at 8:54 p.m. on Tuesday, March 8. By sundown on the 9th, the moon will have moved to a position nearly 9.5 degrees above the horizon. Sunset is essentially at 6 p.m., and moonset will be an hour later. Between 30-40 minutes after sundown, an ultra thin, one percent lit crescent moon will be seen (probably using binoculars) about three degrees above the horizon just to the south of west. A flawless western horizon is necessary. A much less difficult observation of a 5 percent lit crescent moon will be visible the following evening, March 10. By 45 minutes after sundown, the sky will be dark enough to see the moon easily, and Luna will be still 14 degrees above the western horizon. That will be an easy observation that can be made without binoculars, but will be greatly enhanced with their use. Look for earthshine, light from a nearly full Earth being reflected back to us from the unlit portions of the moon. If the air is clear, you should be able to see the earthshine by looking at the moon directly; but its effect will be enhanced if you look away from the moon, and use averted vision to see it. The rods, which are in the peripheral area of the eyes, are more sensitive to low light than the cones found in the central vision. This will also work when using binoculars. Earthshine should also be seen under clear conditions on March 11 and 12. Donít forget to set your clocks ahead by one hour before bedtime on March 13 as we jump ahead to Daylight Saving Time, causing Sol to rise and set later, better syncing it with our time awake.

1021    MARCH 13, 2016:   Wobbling Earth
Astronomers are confronted with the daunting task of tracking the movements of Earth, as well as the independent motions of the moon, planets, and stars, along with everything else that orbits or oscillates. Itís a complicated task, but if we are to send a spacecraft to target a location on the moon or a distant planet, or pinpoint a telescopeís position to image a faint galaxy, astronomers must know its location against a frame of reference to a high degree of accuracy. One Earth motion which affects the position of stars is called precession. If a force is applied to the axis of a rotating top, the axis will move in a plane that is perpendicular to the applied force. The Earth is a tilted, rotating top with its equatorial regions bulging outward due to its spinning motion. The sunís net gravitational effect on all parts of this swelling pulls harder on the region of the bulge closest to the sun, trying to right Earthís axis and bring Earthís equator into alignment with its orbital plane, called the ecliptic. The moon also contributes to Earthís precessional cycle because it orbits in a plane which is near to the ecliptic. The resulting action, just like the top spinning on a desk, is to cause the Earthís axis to wobble. Unlike the earthbound top which increases in the magnitude of its wobble, the amplitude of Earthís 26,000-year wobble is very stable. In other words, Earthís axial tilt changes very little. Precession causes the civil year, marked by our calendars to be a shorter duration than the actual time it takes the Earth to orbit the sun. As the Earthís axis slowly pivots, the seasonal constellations regress against the fixed dates of the calendar. New pole stars will replace Polaris. By 14,000 AD the fifth brightest star of the night, Vega will be the new ďPolarisĒ and the Northern Hemisphere will be closer to the sun in the summer. Holy Hannah! There goes 10,000 years of lesson plans except for the ones dealing with the seasons. They still will be the result of Earthís axial tilt and not its distance from the sun.

1022    MARCH 20, 2016:   Finally Spring
We made it to spring, and the official moment occurred at 12:30 a.m. EDT, March 20. Of course, if you lived in the Central, Mountain, or the Pacific Time Zone, then the first moment of spring happened on the 19th at 11:30, 10:30, and 9:30 p.m. respectively. At that moment the sun was poised exactly over the vernal equinox, the origin point in the sky where the sunís path crossed the celestial equator, Earthís terrestrial equator projected into space. At that time the sun stood at the zenith on the equator, and in the next moment, passed into the Northern Hemisphere where Sol will remain favoring us until 10:21 a.m., EDT, September 22 when it will once again stand over the equator, but now will be headed southward into the Southern Hemisphere. This really should be our New Year because it is the successive crossings of the sun over the vernal equinox that give us the beat of our civil year, the rhythm that governs our calendars and not the actual orbiting of the Earth around the sun. Our orbit takes 365.25636 days and is called the sidereal year. Two crossings of the vernal equinox take 365.24219 days which keeps our calendar dates in sync with the seasons. The civil year, also known as the tropical year, is 20 minutes, 24.5 seconds shorter than the Earthís orbital period which is denoted as the sidereal year. Another curious factor is that if you count the interval of time between the vernal and autumnal equinoxes and the interval of time between the autumnal and vernal equinoxes (and I did), you get an interval of time slightly over 7.5 days longer between the first day of spring and the first day of autumn. This is because the Earth orbits the sun in an ellipse, getting closest to the sun in early January and farthest from Sol in early July. This change in distance is reflected in the orbital velocity of the Earth, which is slower from spring to autumn when the Earth is at a greater distance from the sun. The date of greatest distance can occur from July 3rd through 6th of each year.

1023    MARCH 27, 2016:   Jupiter Ascending
There is no question that the planet Jupiter is reigning supreme as the brightest wanderer in the sky until the middle of summer when Venus will begin to enter the celestial stage. The king of the gods, Jupiter, is below the king of the beasts, Leo the Lion. They are already leaping over the treetops by dark. By 10:30 p.m. Jupiter is nearly due south on the meridian and as high as it can get in the sky. Fast forward a month to the end of April, and Jupiter will be in the south by 8:30 p.m. before it is fully dark. Telescopically, Jupiter probably offers the easiest planetary detail to witness through small scopes. Donít expect to see the Red Spot, but Jupiterís two equatorial belts are easily visible. Look for these dark bands straddling the equator, and youíll be witnessing Jovian meteorology in action. Jupiter is very hot inside, and its weather is created by this leftover heat that accumulated from Joveís birth 4.5 billion years ago. As heat rises from Jupiterís turbulent interior, it pushes small amounts of ammonia gas to higher altitudes where it cools and condenses to form ammonia snow. These bright areas are called zones on Jupiter. The ammonia and other gases, now cooler and denser, move back downward and liquefy into the darker belts. The zebra patterns of alternating zones and belts result from Jupiterís rapid rotation which stretches and regiments these areas of uplift and downdraft to specific regions north and south of Jupiterís equator. Perhaps even more enjoyable is watching the interplay of Jupiterís four bright Galilean satellites, Io, Europa, Ganymede, and Callisto. They orbit the planet in periods of 1.8, 3.6, 7.2, and 16.7 days, and because they are positioned in Jupiterís equatorial plane, they stretch out like tiny dancers engaged in a complicated routine, sometimes all to one side, or two and two, or tucked close to their giant parent world. Their ever changing patterns which are easy to discern make Jupiter the most changeable of the eight planets to observe.

[Mid-March 2016 Jupiter]
The equatorial belts of Jupiter are easily delineated in these mid-March images of the Jovian world. Photo by Peter K. Detterline, Douglassville, PA...

[March Star Map]

[March Moon Phase Calendar]