Sunday Evening Eclipse: Clear Sky Expected

September 25, 2015

There will be a total lunar eclipse at a convenient time along with clear skies…what could be better?

Sunday evening we’ll be treated to not only a total lunar eclipse (not TOO uncommon), but a “super” moon at the same time.  That hasn’t happened in many years.  What does it mean?  A good evening to go outside and check out the sky.

A total lunar eclipse happens when our shadow passes over the moon.  That means if you are on the moon you would see earth passing in front of the sun.  The progression is something like this image from Sky & Telescope magazine:

Fujii_Eclipse-1024x496

In the case of Sunday evening, the eclipse will have almost reached totality when the moon rises over the Cascades (when viewed from the western valleys of OR/WA).  Then just 15 minutes later we’ll be in totality…for the next hour and 12 minutes.

MarkTotalLunarEclipse1

After that time a bright slice of the moon will appear and gradually grow larger over the following hour or so as things return to normal.  So what about the SUPER part?  Well, there’s a bunch of media drama there because it’ll barely be noticeable as this graphic shows:

MarkMoon_Huge

There is a 14% size difference between full moons.  I bet you didn’t know that!  It’s because the orbit around the earth is slightly elliptical, not a perfect circle.  The difference between the closest and farthest moon locations is only 30,000 miles, so our eyes can’t even tell the difference from one full moon to the next.  It’s interesting to note that the term SUPER MOON existed from the last 1970s to the late 2000s, but hardly anyone had heard about it until 2011 when the media picked up on it.

Finally, it is sometimes called the “Blood Moon” because of a reddish hue during totality.  That’s due to light from earth’s atmosphere filtering onto the surface of the moon.

Umbra_color_schematic

The weather looks excellent Sunday evening with mainly or all clear skies across the entire Pacific Northwest.  Enjoy the show!

A far more detailed explanation of all this is at Sky and Telescope’s web site.  It’s a great one to bookmark for future events.

Chief Meteorologist Mark Nelsen