Pear Tree Observatory

The first item listed in Charles Messier’s list of not comets is a supernova remnant in the constellation Taurus.  It was recorded by Arabic, Chinese and Japanese observers in 1054 and was visible in broad daylight.  It is 6500 light years away and by now has a diameter of 11 light years.  It is expanding at a rate of 3,355,404 mph.

The Crab Nebula (M 1) [L:30x30s;R:30x30s;G:30x30s;B:30x30s]

The nebula is one of the brightest high-energy sources in the sky. For 40+ years the X-ray energy emitted was considered steady enough to be used as a calibration target. In fact, it was steady enough to have a unit of measure defined based on its output. That unit, a Crab, may have to be re-visited as close examination of X-ray output using a newer more sensitive sensor has shown a totally unexpected variability. Data taken over two years show an intensity decline of about 7%.

The Helix Nebula is one of the closest and brightest of the planetary nebulae in our sky.  Distance estimates range from 450 to 700 light years.  At the larger estimated distance the nebula’s size would be 2.5 LY across. 

The nebula consists of a bright inner ring and a faint outer ring, both consisting of the dying star’s ejected atmosphere.  The faint outer ring is just visible to the upper right of the bright inner ring in the image below.  Although it is one of the brightest planetary nebula, that brightness is spread across a large area making it a difficult object to view visually.  The outer ring has a angular size of 28 arc minutes making it about the size of the full moon.   The outer ring is expanding at a rate of about 89,500 MPH and the inner ring about 71,500 MPH.  Those speeds and size indicate the nebula is about 10,600 years old.

“The Helix Nebula” (NGC 7293) [C:55x120s]

In 1949, when Edwin Hubble was given the honor of taking the first photograph with the new 200″ Hale telescope at Palomar Observatory, this is the object he chose.  It is a reflection nebula lit by a nearby star that he had studied earlier in his career at Yerkes observatory.  What makes this nebula so interesting is its ability to visibly change appearance over the space of several weeks.  The current theory for the rapid visual change is dense dust clouds orbit the star and during their orbit pass between the star and the nebula.  We see the changing shadows the dark clouds cast onto the nebula.

”]The nebula and its associated variable star are both located in the constellation Monoceros (The Unicorn). Variable stars are cataloged by letter designation. Historically, the first identified in a constellation was given the letter ‘R’.  The subsequent discoveries were given ‘S’ through ‘Z’.  The letter designation is combined with the genitive form of the name of the constellation the star is in.  The variable star that lights up Hubble’s Variable Nebula is R Monocerotis.  Most constellations have so many variable stars that the alphabet runs out of letters.  Once that happens a more complex system is used to name them.

This image is a stack of 30 ten second exposures taken on the 2nd of January.