Archive for January 30, 2018

01/30/2018 – Ephemeris – Looking for tomorrow’s lunar eclipse

January 30, 2018 1 comment

Ephemeris for Tuesday, January 30th. The Sun will rise at 8:04. It’ll be up for 9 hours and 44 minutes, setting at 5:48. The Moon, 1 day before full, will set at 8:04 tomorrow morning.

At a bit before 5 this morning the Moon passed perigee, it closest approach to the Earth in its monthly orbit of the Earth. It was 223,072 miles (359,000 km) away. That makes tonight’s Moon, 12 hours or less before full, a super moon. It will rise tonight at about 5:01. However it’s setting that is of interest because it will be in eclipse. The partial phase of tomorrow morning’s lunar eclipse will begin at 6:48 a.m. (11:48 UT), when the upper left part of the Moon will enter the Earth’s inner shadow, called the umbra. The Moon will be fully immersed in the shadow beginning at 7:51 a.m. (12:51 UT). It will probably disappear by then because the Sun will rise just after 8 a.m. and the Moon will set, at least in the Interlochen/Traverse City area at, 8:04.

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


Partial eclipsed Moon

The partially eclipsed Moon in twilight at 7:40 a.m. January 31, 2018 from Traverse City, MI as simulated by Stellarium.

The following is an article I submitted to Green Elk Rapids website that was also published in the Elk Rapids News.  Elk Rapids is a village about 20 miles north of Traverse City on the east shore of Grand Traverse Bay.  I added the metric units for this post.

We will have a calendrical coincidence on January 31st along with a natural event, and just missing another natural event all having to do with the Moon. The first is that the full moon on January fits one of the definitions for a “blue moon”, the second full moon in a month. Of course the Moon doesn’t actually turn blue. It doesn’t really care. Since February is shorter than a lunation, a lunar month, it will not have a full moon. However March will have two full moons like January.

The second is a real event. The Moon being opposite the Sun in the sky, the definition of a full moon, will pass into the Earth’s shadow causing a lunar eclipse or eclipse of the Moon. In this case, a total eclipse. A lunar eclipse of some type occurs in about one in six full moons. We only have to be on the night side of the Earth to see it. That’s the rub this time, because the eclipse will be in progress at sunrise. The partial phase starts at 6:48 a.m. From about 6:30 on the upper left part of the Moon will appear dusky as the Moon sinks deeper in the Earth’s outer shadow, where the Sun is only partially blocked. The Moon will sink farther and farther into the Earth’s inner shadow called the umbra until at 7:51 a.m. it will be totally immersed. By then the sky will be quite bright, with sunrise to occur at 8:02. The Moon should completely disappear and will set unseen at 8:04. Folks a few states west of us will see, more than likely, a coppery colored totally eclipsed Moon. Some TV preacher some years ago called it a blood moon, hoping to sell books about the end times.*

The color comes from the sum of all the sunrise and sunsets happening on Earth at that instant. The red sunrise we see is caused by the blue light being scattered out of the Sun’s light by molecules in the Earth’s atmosphere. It gives us the blue sky. Our atmosphere also bends the Sun’s light. When we see the full disc of the Sun just clear the horizon, it’s still actually fully below the horizon. The light of the sunrise that passes over our heads continues on, being bent further and becoming redder, and fills the Earth’s shadow by the time it reaches the Moon’s distance, making the Moon red. Volcanic ash in the upper atmosphere can make the Moon almost disappear during totality.

This full moon is also a so-called “super moon”. These occur when the full moon is nearest the Earth in its monthly orbit of the Earth. January first’s full moon was the closest of the year, you might say a super-duper moon. The Moon reached its perigee, closest point or 221,581 miles (356,600 km) away 5 hours before the Moon was officially full. This time perigee is the day before full, about 1,500 miles (2,400 km) farther away. These are measured center to center. The closest an Elk Rapids observer will be to the Moon on the 31st will be at about 12:30 a.m. at 219,920 miles (353,927 km), subtracting most of the Earth’s radius. Of course the Moon won’t look that big being high in the south then. By moon set it will retreat to 223,778 miles (360,136 km) from an Elk Rapids observer. The increased apparent size of the rising or setting Sun or Moon is an optical illusion. The Moon is closer to us when high in the sky than when on the horizon.

The next lunar eclipse visible to us is next year, on the night of January 20-21, 2019.

* The Elk Rapids News didn’t like my dig about the TV preacher and omitted this sentence.  I rather expected them to.

Lunar Eclipse January 31, 2018

Credit NASA.

The original page for this graphic is:

    Total Lunar Eclipse January 31
Event               Time EST   Time UT
                    GT Area    
Enter penumbra      5:51 a.m.  10:51   Unseen
Begin partial phase 6:48 a.m.  11:48
Totality begins     7:51 a.m.  12:51
Sun rises           8:02 a.m.
Moon sets           8:04 a.m.
Mid eclipse                    13:28
Totality ends                  14:07
End partial phase              15:11
Leave penumbra                 16:08   Unseen

The shading of the penumbra is generally noticeable within 1/2
hour before the partial phase begins and again after it ends.