Moon and Planets, April 2011

Look southeast in mid-April for the Moon, Saturn and Spica

Podcast above is from Abrams Planetarium.

April 2011 brings more daylight hours.  On April 1st, the sun is in the sky for about 12 hours, 45 minutes in the northern part of the United States.  By April 30, the daylight hours increase to 14 hours.

Saturn is the only bright planet that shines throughout the night this month.  The yellowish ringed planet rises in the eastern sky around sunset, is in the southern sky at midnight, and sets in the western sky near sunrise.    On April 2, Saturn is at oppostion; that is, it is opposite the sun in the sky.  At this time, our planet is directly betwen the sun and Saturn.  Saturn takes nearly 30 years to revolve around the sun, but because of its slower speed, Earth catches up to and passes Saturn every 378 days (1 year, 13 days).  In 2012, Saturn’s opposition is April 15.

On April 16, the moon appears near Saturn and Spica.  Use the moon as a guide at mid-month to locate those objects.  Saturn is distinctly yellow and the star Spica is blue in color.  The chart above shows the moon, Saturn and Spica on April 16 at 9 p.m.

In contrast, Venus and Mercury are never seen at midnight from the skies of Earth.  Both planets are between the earth and sun.  Because of this geometry, the two planets are seen near sun, either in the west after sunset or in the east before sunrise.  With Mercury being closer to the sun, it is rarely seen in a dark sky.  Unless the moon, bright planet or bright star is the vicinity, Mercury goes unnoticed.  In contrast, Venus is farther from the sun and can appear high in the east before sunrise or in the west after sunset.  Because of its brilliance, Venus has been called the “Morning Star” or “Evening Star.”  Generically, any bright planet can be given those names.

Mercury was visible in March in the evening sky.  By early April, its rapid revolution carries it between the sun and Earth (inferior conjunction) and into the morning sky.  During the past several weeks, brilliant Venus has moved farther from Earth, appearing low in the eastern predawn sky.  The manner in which we view the solar system during spring mornings places the planets low in the sky. 

Similarly, Jupiter was visible in the western sky at sunset during March.  From our view on Earth, Jupiter passes behind the sun (conjunction) early in April and moves into the morning sky.  Jupiter moves at about twice the speed of Saturn around the sun, yet Earth catches up and passes Jupiter every year and 34 days.  In contrast, Mars moves about half the speed of Earth and our planet catches it every 2 years, 50 days.

Look for a planetary grouping at the end of April, 2011.

In late April 2011, four planets are clustered near the horizon.  This occurs in bright twilight, so a binocular or telescope is necessary to locate these objects.  As shown in the diagram above on April 30 at 5:30 a.m., a crescent moon appears above bright Venus.  Dimmer Mercury appears to the lower left of Venus.  Both Mars and Jupiter appear just above the horizon.

 
As the calendar turns into May, Jupiter, Mars and Venus will make additional interesting planetary groups.  Be sure to check back in early May 2011 for that month’s update.
Advertisements

Moon and Planets, March 2011

 
Moon and Planets
Look in the west for Jupiter, Mercury and the moon in the evenings during early March.

 

The podcast player shown above for the month of March 2011 is from Abrams Planetarium.

March is a month of rapid change.  Weather shuffles from the depths of winter into the promises of May.  This year the Moon and planets provide interesting views during the early evening and early morning.

Early in the month, Jupiter, Mercury, and the moon appear in the western sky after sunset.  The moon will appear as a very thin crescent.  As the diagram above shows, the moon,  just 46 hours past its new phase, and Jupiter make an interesting display during twilight on March 6 with elusive Mercury much lower and near the horizon.  Houses, trees and other terrestrial features will block a view of Mercury.  Binoculars will help locate it from a spot with a clear horizon.  The accompanying chart shows the trio at 6:15 p.m.

Mercury is difficult to view, although twice each year in our planet’s celestial orbit, we can get an optimal view of the planet.  During spring evenings and autumn mornings, we have an excellent view of the solar system objects that are near the sun.  Because of Mercury’s solar proximity, it always sets before the sky completely darkens.  During spring and autumn the solar system is oriented so that Mercury sets later than average or rises sooner than its average time, making it best viewed if it is appropriately placed in its orbit.

Look for Jupiter and Mercury during mid-March.

 As the days of March step forward, watch Mercury climb higher in the sky each evening at 6:15 p.m.  (Remember that Daylight Saving Time begins March 13.  Beginning on that date the times will advance one hour.)  By March 15, Jupiter and Mercury appear near each other at 7:30 p.m. (See the diagram above.) Mercury will continue to climb higher for another week and then rapidly dim and disappear into the sun’s bright glare by month’s end. 

At the end of March look for Venus and a thin crescent moon just before sunrise.
By the end of March, the moon will appear in the morning sky.  On the last day of the month, a thin waning crescent moon, less than 3 days before it’s new phase, appears near Venus at 6 a.m. in the eastern sky.
 
March is a fascinating month of change in the weather, the promise of longer, warmer days, and bright configurations of the moon and planets.
 

Winter Solstice Lunar Eclipse

(NASA Photo)

A spectacular lunar eclipse is visible across the skies of North America, just hours before the winter solstice, on the night of December 20/21, 2010.

A lunar eclipse is visible when the moon, at the full phase, moves into the Earth’s shadow.  Occurring infrequently because the orbit is tilted slightly compared to the earth’s solar orbital path, the moon usually moves above or below the shadow when on the opposite side of Earth from the sun.

As the moon slowly plunges into the Earth’s shadow, it loses its reflected sunlight.  A total eclipse is not completely dark, but some red and orange sunlight is refracted into the shadow.  The moon then has a reddish orange glow.

Earth’s shadow has two zones:  The penumbra is the outer part of the shadow where the sunlight is not completely blocked.  The umbra is dark because it receives no direct sunlight.  During the nighttime we are inside the earth’s umbra.  No sunlight is visible.

Lunar eclipses are seen more often from any one location as they are visible from over half the earth, where the moon is above the horizon.  A lunar eclipse is not dangerous to view.  Binoculars or a telescope under low power, 15x to 40x present outstanding views of the eclipse.

Here are the events for the evening:

December 20, 2010  (The times that follow are accurate for any location in North American, except times for sunrise, sunset, moonrise, and moonset.  Observers in other time zones can adjust the eclipse times by adding or subtracting their time zone difference from Central Standard Time.)

  • 3:50 p.m. CST (Chicago) — The moon rises in the east-northeast sky.
  • 4:22 p.m. CST — Sunset.  Throughout the evening, the moon rises higher in the eastern sky.
  • 11:30 p.m. CST — The moon begins to move into the penumbra.  Not much darkening is noticed.

December 21, 2010

  • 12:32 a.m. CST — The moon moves into the darker central shadow, the umbra.  The partial phases of the eclipse begins.  As the eclipse progresses, more of the moon grows darker.  The moon appears high in the southern sky during this part of the eclipse.
  • 1:40 a.m. CST — The moon is completely immersed inside the umbral shadow and the best part of the eclipse begins.  For the next 73 minutes, the moon may be illuminated by a soft coppery color, like the image above.  Some sunlight streams through the earth’s atmosphere and is bent into the shadow by the air’s prismatic effects.  The brightness and depth of color will depend on the amount of dust suspended in the Earth’s atmosphere.  Volcanic ash suspended at high altitudes is one factor that can affect the colorful display.
  • 2:53 a.m. CST — The moon begins to exit the umbra and the total phase of the eclipse is finished. 
  • 4:01 a.m. CST — The moon is fully inside the penumbra continuing to exit into bright sunshine.
  • 5:04 a.m. CST — The eclipse is finished.
  • 7:14 a.m. CST — Sunrise
  • 7:31 a.m. CST — Moonset
  • 5:38 p.m. CST — Winter Solstice

The next lunar eclipse visible from North America occurs on June 4, 2012.  The start of the eclipse occurs June 4, 2012, although it completes after moonset.  The next total lunar eclipse visible from the Americas is on the night of April 14/15, 2014.

For more information about lunar eclipses and general sky watching, see the Waubonsie Valley High School Planetarium website.