The Sky This Week, April 14 – 21, 2015 !

The Sky This Week, 2015 April 14 – 21

What lies beyond
Markarian’s Chain, the heart of the Coma-Virgo Galaxy Cluster
Messier 86 and 84 are the two prominent galaxies at center-right
Imaged from Morattico, Virginia on 2013 April 14.

The Moon spends the majority of the week in twilight skies, visible before sunrise as the week opens and returning to the evening sky as it closes.  New Moon occurs on the 18th at 2:57 pm Eastern Daylight Time.  Look for Luna in the early evenings of the 20th and 21st near the bright glow of the planet Venus.  On the 21st she forms an attractive triangle with Venus and the bright star Aldebaran in Taurus.

Global Astronomy Month continues with the observance of International Dark-Sky Week.  Sponsored by the International Dark-Sky Association, the week-long focus on dark skies was started in 2003 by high-school student Jennifer Barlow.  Now in its twelfth year, it is a key awareness program for Global Astronomy Month.  Its objectives are to 1) inspire people to celebrate the beauty of the night sky, 2) raise awareness about the negative effects of light pollution, and 3) embolden folks to Take Action!  Light pollution not only affects astronomers by limiting their ability to view faint, distant celestial objects, it has also been found to affect the life-cycles of migratory birds, sea turtles, and a host of our fellow species on the planet.  There is also increasing medical evidence that artificial night lighting is a serious health issue for many people.  It has been shown to affect circadian rhythms, which have in turn been linked to which to other chronic disorders.  More information on International Dark-Sky Week may be found here.  In addition to the above, the April campaign for the Globe at Night Observing program continues until the 19th.  Go out and observe Leo, the Lion and report your findings to the program’s website to help chart the distribution of light-polluted skies.

Last week we featured the dim constellation of Coma Berenices, a loose agglomeration of relatively nearby stars that form a gauzy haze to the naked eye just east of Denebola, the star that marks the “tail” of Leo, the Lion.  This is the area that contains the north pole of the Milky Way Galaxy, so gazing in this direction takes our sight line directly away from the dense star fields of our home star system.  It’s no surprise therefore, that beyond the few stars in the area there is an abundance of distant external galaxies, many of which can be tracked down in small- to medium-sized telescopes.  Most of these galaxies are part of a huge grouping known as the Coma-Virgo galaxy cluster.  About 1500 galaxies are a part of this cluster, including our own Milky Way.  The center of the cluster consists of three massive elliptical galaxies, numbers 84, 86, and 87 in Charles Messier’s 18th-Century catalog of “nebulae”.  Each of these systems, located some 55 million light-years from the Earth, contains over a trillion stars and represent some of the largest galaxies known.  M87, in particular, is noted for the massive black hole at its center that causes the galaxy to eject matter along bright “jets” of light and radio emissions

Venus presses eastward this week, leaving the Pleiades star cluster in her wake as she heads toward the stars that depict the “horns” of Taurus, the Bull.  She passes about 7 degrees north of the bright star Aldebaran on the evening of the 19th.  Two nights later the waxing crescent Moon joins Venus and the star in what should be a colorful and attractive photo opportunity.

Jupiter is high in the south as evening twilight falls.  You should be able to spot him shortly after sunset, and by the time twilight ends he stares down with a bright yellow gleam.  Old Jove is approaching the point known as Quadrature in his current apparition, which means that the Sun strikes the planet at an angle of about 10 degrees from Earth’s point of view.  This causes the planet’s moons to cross the disc well ahead of their shadows.  You can see a prime example of this in a small telescope on the evening of the 15th, when the moon Europa’s shadow begins transiting the planet at around 8:30 pm.  At 8:55 Europa moves off the disc of the planet, but its shadow won’t finish its transit until 11:21 pm.

Saturn now rises well before 11:00 pm in the southeastern sky, nestled among the bright stars of the head of Scorpius.  The ringed planet is still best seen in the wee hours, crossing the meridian at around 3:30 am, but early risers can still catch a glimpse of him in gathering morning twilight.  Saturn will gradually move into the evening sky over the next few weeks, reaching opposition in just over a month.


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