Bob Moler's Ephemeris Blog

Ephemeris for Tuesday, September 1st.  The Sun will rise at 7:04.  It’ll be up for 13 hours and 15 minutes, setting at 8:19.   The Moon, 3 days past full, will rise at 10:07 this evening.

Today in part 2 of the September preview we look ahead at this month’s total lunar eclipse on Sunday evening the 27th.  This is the last of four total lunar eclipses in a row that started last year April, continuing last October and this April.  Only this past April’s eclipse was visible in clear skies here, but all we could see was the beginning partial phase from here.  We will get to see, clouds willing, the whole eclipse between 9 p.m. and 12:30 a.m.  Lunar eclipses only can occur at full moon, when the Sun, Earth and Moon are lined up so that the Earth’s shadow falls on the Moon.  The Moon will be completely immersed in the Earth’s shadow for over an hour then.  You can mark it on your calendars, but I will be reminding you about it all the week before.

Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

The following is my article from September’s newsletter of the Grand Traverse Astronomical Society the Stellar Sentinel.  Note as with the above tines, the times here are Eastern Daylight Time.

The Last of a Quartet of Lunar Eclipses

The last of a quartet or tetrad of consecutive total lunar eclipses will occur Sunday night September 27^th. The others were either clouded out or started too late for totality to be visible from here. We are hoping for good weather for this one.

Lunar eclipses or eclipses of the Moon, as these events are also called, only occur at full moon when the Earth’s shadow is cast upon the Moon. Unlike a solar eclipse, of which the partial phases are dangerous to gaze upon without special protection, a lunar eclipse is perfectly safe to view throughout.

How lunar eclipses occur. Credit NASA/Fred Espenak.

There are three kinds of lunar eclipses or phases of lunar eclipses: penumbral, partial, and total. A total eclipse passes through all three phases. In the penumbra the Sun’s light is increasingly cut off from the outside to the inside of the shadow called the umbra, where all direct sunlight is cut off. Depending on the path of the Moon, it can cut through only the penumbra, in which the eclipse is barely noticeable, a penumbral eclipse; pass only partially through the umbra, a partial eclipse; or immerse completely in the umbra to produce a total eclipse.

Lunar eclipses are easiest to see, because one only has to be on the night side of the Earth to see it. In a solar eclipse, the Moon’s shadow is too small to cover the earth, since it’s only a quarter the size of the Earth, so one has to be in a band a few thousand miles wide to spot the partial phase and has to be in a very narrow couple hundred mile wide path to see the brief totality. We’ll revisit this in 2016 in preparation for the country spanning total solar eclipse of August 21, 2016.

Eclipses, both lunar and solar occur in seasons nearly 6 months apart, which usually have one of each two weeks apart. Occasionally with a central eclipse of one to have two of the other two weeks before and two weeks after.

The reason for this is because the Earth and Moon’s orbits are tilted at about a 5° angle, and the point where they cross, 180° apart is slowly rotating clockwise. This gives us two eclipse seasons a year that slowly move earlier in the calendar. It is only when the Sun is near where the orbital planes cross that we have a chance for an eclipse, otherwise the Moon is too far north or south.

After this eclipse, the next total lunar eclipse will be January 21, 2019. However the Moon will set while in totality for us on that one.

If you’d like to explore eclipses further, check out this NASA website: http://eclipse.gsfc.nasa.gov/eclipse.html.

The eclipse occurs on the 28th for Universal Time. It’s the evening of the 27th for us. The Moon travels through the Earth’s shadow from right to left. What are seen are points of contact with the shadow and mid-eclipse. From Five Millennium Canon of Lunar Eclipses (Espenak & Meeus) NASA.

Contact times are labeled P1, U1, U2, U3, U4, and P4. P2 and P3 are omitted because they are synonymous with U1 and U4 respectively:

• P1 – 8:11:47 p.m. Enter the penumbra (unseen). By about 8:30 the duskiness on the left edge of the moon will start to be noticeable.
• U1 – 9:07:11 p.m. Enter the umbra (partial eclipse begins).
• U2 – 10:11:10 p.m. Totality begins.
• Mid eclipse 10:48:17 p.m.
• U3 – 11:23:05 p.m. Totality ends, egress partial phase begins.
• U4 – 12:27:03 a.m. Partial phase ends. The Moon’s upper right edge should appear dusky for the next half hour or so.
• P4 – 1:22:27 a.m. Penumbral phase ends (unseen).

Note: The duskiness of the penumbral phase of the eclipse can be enhanced by viewing through sunglasses.

During the total phase, light leaks in around the Earth due to the bending of light in the Earth’s atmosphere, so the Moon is illuminated by the collective sunrises and sunsets around the globe. This usually gives the Moon a coppery hue, that some are now calling a blood moon. Occasionally, due to volcanic eruptions the Moon can become very dark.

This full moon is also the Harvest Moon and for those who care, a supermoon, it having reached perigee earlier that day.

Weather permitting there will be two GTAS venues in northern lower Michigan to view this eclipse. The first will be the Northwestern Michigan College Rogers Observatory, south of Traverse City, MI. The second will be at the Sleeping Bear Dunes National Lakeshore at Platte River Point at the end of Lake Michigan Road off M22. These sites will be open for the visible parts of the eclipse from 9 to midnight.

Of course the eclipse can be seen from your yard with no optical aide whatsoever.

The partially eclipsed Moon setting through a thin clouds and the neighbor’s swing set at 7:09 EDT April 4, 2015. Taken with a Motorola Droid Razr phone through 10X50 binoculars. Credit: Bob Moler.