The Sky This Month – April 2015

Lunar Eclipse4 April 2015. Full Moon, 13:05 UT. (The “Pink Moon”, “Egg Moon”, or “Grass Moon”).

4 April. A brief lunar eclipse occurs near today’s Full Moon just two weeks after last month’s total solar eclipse. Many lunar eclipses last an hour or more, but this one is unusually short. It lasts just under five minutes, from 11:58 UT to just past 12:02 UT. Observers in the eastern half of Australia and all of New Zealand and Hawaii can see the entire eclipse. In western North America, the total eclipse will be visible in the pre-dawn sky, but the Moon will set before the eclipse ends. Observers in eastern North America and most of South America will see the Moon set before the eclipse reaches totality.

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Satellite Trails in the Southern Skies

img_10142-cc-1024x394This stunning wide-angle view of the southern Milky Way from ESO’s Paranal Observatory shows the galactic center near Sagittarius at lower left, the beautiful section in Centaurus and through the Southern Cross at top, and down through Carina and Vela towards the right. The famous Magellanic clouds surround the dome at lower right. And in the short time during which this image was made, 15 Earth satellites and 2 planes passed across the sky. Can you find their trails? Click on the image above for a close up…

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Caroline’s Cluster

NGC 2360 (Caroline's Cluster)

NGC 2360, Caroline’s Cluster (credit: Roberto Mura)

The constellation Canis Major, the Big Dog, contains a handful of splendid star clusters for observers with a small telescope. Messier 41 is the most famous and easiest to see. The lesser known NGC 2362 is fainter, but prettier. And the lovely star cluster NGC 2360 is always worth a careful gaze as it occupies a particularly rich section of the Milky Way. This open star cluster was first discovered by Caroline Herschel on February 26, 1783 using a small refractor. Her famous brother William Herschel included the cluster in a later catalog of 1000 deep-sky objects that he and his sister discovered. In her honor, the cluster is sometimes called “Caroline’s Cluster”.

Caroline’s Cluster is easy to find about 3.5º east of the blue-white star star γ Canis Majoris, sometimes called Muliphein, one of the three stars in the head of the Big Dog (see image below). At magnitude 7.2, the cluster is bright enough to spot in binoculars. It’s also compact, which means it has high surface brightness. So it’s easy to pick out even in moderately light-polluted skies.

Location of "Caroline's Cluster", NGC 2360, east of the head of Canis Major.

Location of “Caroline’s Cluster”, NGC 2360, east of the head of Canis Major.

In binoculars, NGC 2360 appears diffuse and unresolved and spans about half the size of the full Moon. The cluster lies embedded in a rich field of stars along the plane of the Milky Way. In a telescope, the cluster is cracked open into dozens of 9th to 12th magnitude stars that are centered around an elliptical core, which curved branches poking out to the east and west. About half a degree to the west lies a bright 5th-magnitude star which is not a member of the cluster.

The cluster is old for an open cluster, with an estimated age of about 2.2 billion years. So you see very few bright blue-white stars here. Such stars, which burn fast and die young, have long ago exploded or faded away.

NGC 2360 lies about 3,700 light years away.


Red Barns and the Physics of Dying Stars

The pigment in red paint is made from plentiful elements cooked inside dying stars (image credit: Ian Britton)

The pigment in red paint is made from plentiful elements cooked inside massive dying stars (image credit: Ian Britton)

Why are so many barns painted red? The answer to this seemingly simple question goes deep into the physics of massive stars at the end of their lives. In 2013, a Google employee named Yonatan Zunger posted a long explanation on his Google+ page.  Summarized here, Zunger explains that barns are painted red because red paint is cheap. And red paint is cheap because its made of Fe2O3 (red ochre) composed of iron and oxygen. And iron and oxygen are cheap because they are plentiful on Earth because they formed readily in the innards of massive stars when the end their lives as supernovae explosions.

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