The Sky This Month – April 2010

Overview

In mid-December about six years ago, your publisher rode in a taxi to a meeting in suburban Dallas, Texas.  My young taxi driver hadn’t met many Canadians before, and he was curious about the legendary Canadian winters.  “So when does the snow finally melt in Canada”, he asked as he sipped his coffee.  I told him it was usually gone by, oh, about mid-April.  He nearly choked on his coffee.  “Snow until April?  Whoa… that’s harsh, man.  That’s harsh!!”

Indeed.

But April’s arrived and the snow has melted ahead of schedule.  A few flowers bloom in central Canada, and fair-weather astronomers poke their heads out to see what the sky offers this month.  There’s much to see… the galaxy fields of Leo and Virgo and Coma Berenices, a few lingering open star clusters in the southern constellations Carina, Crux, and Centarus, and the planets Mercury, Venus, Mars, and Saturn well placed for viewing.

So let’s get to it.

A hundred Aprils wouldn’t be enough to see all the galaxies in Leo, Virgo, and Coma Berenices visible in a good-sized backyard scope.  Some galaxies are prettier than others, with NGC4565, M64, and M87 among our favorites.  Nearly all belong to the Virgo Cluster, the closest major galaxy cluster to our own, some 60 million light years away.

The constellation Coma Berenices has a very romantic history based in antiquity, as recounted in Stargazing for Beginners…

“The young Queen Berenice, when her husband was called away to the wars, vowed to sacrifice her beautiful tresses to Venus if he returned victorious over his enemies.

He did return home in triumph, and Berenice, true to her vow, cut off her hair and bore it to the Temple of Venus. But the same night it disappeared. The king was furious, and the queen wept bitterly over the loss.

There is no telling what might have happened to the guardians of the temple, had not a celebrated astronomer named Conon led the young king and queen aside in the evening and showed them the missing locks shining transfigured in the sky. He assured them that Venus had placed Berenice’s lustrous ringlets among the stars, and, as they were not skilled in celestial lore, they were quite ready to believe that the silvery swarm they saw near Arcturus had never been there before.

And so for centuries the world has recognized the constellation of Berenice’s Hair.”

Coma itself is a sparse and dispersed star cluster.  It’s lovely in binoculars and vaguely cloud-like to the unaided eye.  Without bright guide stars, it’s a challenge to navigate the faint galaxies in this area.   The image below shows a slice of sky just east of Denebola, at the edge of Leo, that helps you find a T-shaped group of stars of which 6 Coma is the brightest.  Around this “T” you’ll find the three spiral galaxies M98, M99, and M100.  While not trivial to find, these galaxies were spotted by Charles Messier with his modest 2-inch scope.

M98, M99, and M100 in Coma Berenices

And yes, all this is visible from the southern hemisphere too, just above the north-east horizon before midnight local time.

Moon

Last Quarter: April 6, 9:37 UT
New Moon: April 14, 12:29 UT
First Quarter: April 21, 18:20 UT
Full Moon: April 28, 12:18 UT

Look for the slender crescent moon on April 15-16 as it hangs just a couple degrees away from Mercury and Venus in the western sky just after sunset.

Planets

Mercury reaches its greatest elongation from the sun on April 8 and puts on its best show this year.  The first two weeks of April are the best time to see this swift little world as it lies more than 10 degrees above the horizon and shines as bright as magnitude -0.9.  Many stargazers have never seen Mercury.  Even the great Nicholas Copernicus never laid eyes on this planet.

Look for Mercury west-northwest about 1/2 hour after sunset.  Binoculars give you an expansive view of the region, which includes Venus 3-5 degrees away and the Pleiades about 7-8 degrees higher.  When the sun is safely set, aim your telescope at Mercury.  You won’t see any surface detail, but you will see a partially-lit tiny disk just 8″ across.  The planet fades in brightness by nearly 80% by month’s end as it sinks back towards the sun.

Venus and Mercury at sunset in the western sky, as they will appear on April 8, 2010

• Venus points the way to Mercury.  It blazes at close to magnitude -4 and lies just a few degrees above Mercury in the western sky after sunset.  It makes its closest to Mercury on April 4.  And at mid-month, a slender crescent moon joins Venus, making an ideal spectacle for an easy astrophoto.  Here’s how to take a good one…

• Mars lingers in the constellation Cancer.  At an average magnitude of +0.5, it’s still respectably bright.  But since December, Earth has sped away from Mars and the planet reveals scant detail in all but the largest backyard telescopes.

• Jupiter rises about an hour before the sun in the southeastern sky.  Not much to see this month.  It’s best left for summer observing this year.

• Saturn.  We’ve covered Saturn in detail in the past week, so just a reminder the planet is up all night this month and ideally-positioned for viewing.  It rises in the east just before sunset, but wait until 9-10 p.m. for the best view.  Here’s an image of where to find it.

• Uranus is lost in the sun this month. Neptune is also just emerging from morning twilight.  Both are better observed in the summer.

Venus, left, and Mercury from Ottawa, Canada, on April 4, 2010

Celestial Events

• As mentioned above, the crescent moon on April 15-16 meets up with Mercury and Venus in the western sky just after sunset.

• From April 14-20, the fading but still bright planet Mars lies just 2 degrees from the Beehive Cluster (M44).  A lovely sight in binoculars

• The Lyrid meteor shower peaks after midnight on April 22.  This shower, with a radiant near the bright star Vega, is not usually impressive.  But there have been exceptions.  This year, the first-quarter moon will set in time to reveal more meteors, which are more plentiful after midnight.

• And this is Global Astronomy Month. Check out what’s happening online and around the world here right here…

A Special Musical Treat This Month…

Many of you know of Sir William Herschel (1738-1822), who discovered the planet Uranus, cataloged hundreds of deep-sky objects with massive telescopes he built himself, and made prescienct predictions of the nature of star clusters and nebulae.

Before Herschel became the most successful astronomer of his time, he was a musician and composer.  One of our readers, Bruce Whitson, an accomplished amateur astronomer and professional viola player in Germany, has organized the recording and exposition of several pieces of Herschel’s music.  He was kind enough to send us a recording of concert of Herschel’s music recorded in Germany.  We posted a piece from one of Herschel’s symphonies to our website yesterday… here’s the link.   It’s darned good… nicely composed and brilliantly performed.