Western Slope Skies - Lunar Eclipse at Dawn

Mar 27, 2015

If you rise early on Saturday, April 4 you will be treated to an unusual event:  the third of four total lunar eclipses occurring within a period of just two years.  This has been called a lunar eclipse tetrad. 

The April 4 eclipse will become obvious around 4:15 a.m. MDT, when the eastern edge of the moon starts to enter Earth’s umbral shadow.  Lunar brightness will steadily diminish until 5:58 a.m., when the eclipse becomes total as the entire face of the moon becomes immersed in Earth’s shadow.   But, the moon will pass through only a small northern part of the shadow on April 4.  Thus the total eclipse will last only 5 minutes, ending at 6:03 a.m.  From the Western Slope, the moon will set at 6:55 a.m., just after sunrise, still in partial eclipse.     

You might expect the Moon to be invisible while totally eclipsed.  But that almost never happens, because our atmosphere bends red light into Earth’s shadow, so the shadow is not completely dark.  This may create a colorful and awe-inspiring effect for western Colorado on April 4:  A reddish moon descending in the west, and fading against the brightening gold of dawn.        

The color and brightness of the totally eclipsed moon can vary from bright, coppery red to very dark, grayish red.  Color and brightness depend on several factors, including how deep the moon penetrates into Earth’s shadow and the abundance of volcanic aerosols and ash in Earth’s atmosphere.  The April 4 total eclipse may be relatively bright, because the moon won’t be penetrating deeply into Earth’s shadow.      

The fourth total lunar eclipse in this “tetrad” will be visible from Colorado on the evening of September 27, 2015.  We’ll have more on that later.   

Western Slope Skies is produced by members of the Black Canyon Astronomical Society.  This episode was written & recorded by Art Trevena.