West Coast Favored for Total Lunar Eclipse on January 31st


Diana Hannikainen, Observing Editor
617-864-7360 x22100, diana@skyandtelescope.com

J. Kelly Beatty, Senior Editor
617-864-7360 x22168, kbeatty@skyandtelescope.com

Note to Editors/Producers: This release is accompanied by high-quality graphics, animations, and video interviews; see the end of this release. For more information, please direct your readers/viewers to our online story about the eclipse (not to this press release, please).

The first total lunar eclipse of 2018 will be a predawn spectacle for western North America.

No one has seen a total eclipse of the Moon since September 27-28, 2015, and now the 2½-year-long drought is finally ending — at least for those living near the West Coast and most everywhere around the Pacific Rim. In North America, a total lunar eclipse occurs before dawn on Wednesday, January 31st.

Weather permitting, those in western North America should see much if not all of the eclipse. Alaska, Hawai'i, Yukon, most of British Columbia, the Northwest Territories, and parts of Nunavut should witness every stage of the eclipse starting well before dawn. The entire eclipse is also visible on the evening of January 31st from eastern and northern Asia, New Zealand, and most of Indonesia and Australia.

According to Sky & Telescope magazine, anyone west of a line running from Chicago to New Orleans will see at least the first part of the Moon's 76-minute-long plunge through Earth's deep shadow. "The farther west you are, the higher the Moon will be in the predawn sky when the eclipse starts — and the more of it you'll see," explains Diana Hannikainen (HAHN-ih-ky-nen), S&T's Observing Editor.

For the eastern U.S. and Canada, the Moon sets (and the Sun rises) as the early stages of the eclipse get under way. Those on the East Coast will see, at best, a dark "bite" extending about halfway across the lunar disk.

See the table below and diagrams at the end for times of key events during January 31st's eclipse. The stages of the eclipse occur simultaneously for everyone who can see the Moon, but the clock times for you depend on your time zone:

A second total lunar eclipse occurs this year on July 27th. It's observable only in the Eastern Hemisphere: Africa, the Middle East, and central Asia. But don't despair: The next total lunar eclipse visible everywhere in North America occurs on January 21, 2019.

What to Look For

This eclipse promises to be a grand one, since it happens one day after the Moon passes its perigee, or the point in its orbit closest to Earth. The Moon will appear about 13% larger in diameter (what has come to be called a "supermoon") than it does when it's at apogee (farthest from Earth). That might not be enough for anyone but dedicated Moon watchers to notice. Still, given the Moon's above-average size and the fact that it's the second full Moon in January (a "blue Moon"), this eclipse is going to get a lot of publicity.

A lunar eclipse happens when the Sun, Earth, and a full Moon form a near-perfect lineup in space. The Moon gradually glides into Earth's shadow, until the entire lunar disk turns from white to an eerie dim orange or red. The total phase of the eclipse will last 1 hour 16 minutes, with its midpoint at 5:30 a.m. PST (13:30 Universal Time). Then events undo themselves in reverse order, until the Moon returns to full brilliance. The whole process for this event will take more than 4 hours.

You only need your eyes to see the drama unfold, but if you have binoculars or a backyard telescope, they'll give a much-enhanced view.

The events that happen to a shadowed Moon are more complex and interesting than many people realize. A total lunar eclipse has five stages, with different things to watch for at each.

(1) The penumbral stage begins when the Moon's leading edge enters the pale outer fringe of Earth's shadow: the penumbra. But the shading is so weak that you won't see anything of it until the Moon is about halfway across the penumbra. Watch for a slight darkening on the Moon's lower-left side as seen from North America.

The penumbra is the region where an astronaut standing on the Moon would see Earth covering only part of the Sun's face. The penumbral shading becomes stronger as the Moon moves deeper in.

(2) The second stage is partial eclipse. This begins much more dramatically when the Moon's leading edge enters the umbra, the cone of Earth's shadow within which the Sun is completely hidden. With a telescope, you can watch the edge of the umbra slowly engulfing one lunar feature after another, as the entire sky begins to grow darker.

The partial phase lasts just over an hour. As its end approaches, only a final bright sliver remains outside the umbra. By this time, the rest of the lunar disk should already be showing a dim, foreboding reddish glow.

(3) The third stage is total eclipse, beginning when the last rim of Moon slips into the umbra. But the Moon won't black out completely: it's sure to glow some shade of intense orange or red.

"That red light you see is sunlight that has skimmed and bent through Earth's atmosphere and continued on through space to the Moon," says Alan MacRobert of Sky & Telescope. "In other words, it's from all the sunrises and sunsets that ring the world at the moment.

"Picture it from the point of view of an astronaut standing on the Moon," says MacRobert. "They would see the dark Earth in the sky thinly ringed with brilliant orange from the Sun hidden behind it. The ring is bright enough to illuminate the ground at the astronaut's feet an eerie red."

The red umbral glow can be quite different from one eclipse to the next. Two main factors affect its brightness and color. The first is simply how deeply the Moon goes into the umbra as it passes through; the center of the umbra is much darker than its edges.

The other factor is the state of Earth's atmosphere along the sunrise-sunset line. If the air is very clear, the eclipse is bright. But if a major volcanic eruption has recently polluted the stratosphere with thin global haze, a lunar eclipse will be dark red, ashen brown, or occasionally almost black.

In addition, blue light is refracted through Earth's clear, ozone-rich upper atmosphere above the thicker layers that produce the red sunrise-sunset colors. This ozone-blue light tints the Moon also, especially near the umbra's edge. The result can be a subtle mix of changing blue, gray, and even green.

(4) As the Moon continues moving along its orbit, events replay in reverse order. The Moon's edge re-emerges into sunlight, ending totality and beginning a partial eclipse again.

(5) When all of the Moon escapes the umbra, only the last, penumbral shading is left. By about 30 or 40 minutes later, nothing unusual remains.

Sky & Telescope is making the following illustrations, animations, and video interviews available to editors and producers. Permission is granted for one-time, nonexclusive use in print and broadcast media, as long as appropriate credits (as noted) are included. Web publication must include a link to SkyandTelescope.com.

World map for Jan 2018 eclipse

This map shows locations worldwide from which the January 31st total lunar eclipse is visible, weather permitting. Because an eclipsed Moon is always full, the Moon sets (or rises) at almost the same time as the Sun rises (or sets) on the opposite horizon. For viewers along the eastern seaboard of North and Central America, the Moon will set before the total phase of the eclipse begins. Those in the Far West, Alaska, Hawai‘i, Australia, and eastern Asia are positioned to see totality in its entirety.
Sky & Telescope

U.S. map of eclipse visibility on Jan 31, 2018

This map shows the parts of North America from which the January 31st total lunar eclipse is visible, weather permitting. Because an eclipsed Moon is always full, the Moon sets (or rises) at almost the same time as the Sun rises (or sets) on the opposite horizon. For viewers along the eastern seaboard of North and Central America, the Moon will set before the total phase of the eclipse begins. Those in the Far West — as well as Alaska, Hawai‘i, Australia, and eastern Asia — are positioned to see totality in its entirety.
Sky & Telescope

Jan 2018 Lunar Eclipse PST

Events for the total lunar eclipse on the morning of January 31, 2018. This version is labeled for Pacific Standard Time (PST). Other versions are available for MST, CST, EST, UT (Universal Time), and unlabeled. Times shown in dark blue mean that event is not visible in most of that time zone. Due to the Moon’s slightly off-center path through Earth’s umbra, the southern half of its disk should look slightly brighter during totality than the northern half.
Sky & Telescope

January 2018 eclipse animation demo

A 36-second-long animation shows the Moon's motion through Earth's shadow on the morning of January 31, 2018. Key events during the eclipse are paused and labeled. Versions are available for specific time zones: EST, CST, MST, PST, unlabeled (with pauses), and unlabeled (without pauses). The penumbra is Earth's outer shadow, which creates a dusky shading on the lunar disk. Portions of the Moon within the much-deeper umbra receive no direct sunlight. However, sunset-colored light refracted (bent) by Earth's atmosphere often creates a reddish or coppery hue on the Moon's face. Where visible, totality lasts for 1 hour 16 minutes.
Sky & Telescope / Ted Mitchell

Moon crossing into Earth's umbra

A partially eclipsed Moon, seen in a long-exposure image by Sky & Telescope contributing photographer Johnny Horne. The right part of the disk is not yet inside Earth's umbra, while the part inside the umbra already shows dramatic red coloring. A background star is just below the Moon.
Sky & Telescope / Johnny Horne

The Moon's progress dead center through the Earth's shadow in July 2000.

Aligning his camera on the same star for nine successive exposures, Sky & Telescope contributing photographer Akira Fujii captured this record of the Moon's progress dead center through Earth's shadow on July 16, 2000.
Sky & Telescope / Akira Fujii

Umbra color schematic

If Earth had no atmosphere, the Moon would look completely black during a total lunar eclipse. However, a little red-hued sunlight refracts through the atmosphere and into Earth's umbra, coloring the lunar disk during totality. (Not shown to scale!)
Sky & Telescope

Sky & Telescope eclipse commentary

Six short eclipse-related commentaries by Diana Hannikainen (Sky & Telescope's Observing Editor) and Kelly Beatty (S&T Senior Editor):
When and where of January 31st's total lunar eclipse (Hannikainen, TRT=00:29)
Appearance of Moon during total eclipse (Hannikainen, TRT=00:30)
Geometry of lunar eclipses (Hannikainen, TRT=00:29)
Coincidence of total lunar eclipse, "Supermoon," and "Blue Moon" (Beatty, TRT=00:55)
Explanation of term "Supermoon" or full Moon at perigee (Beatty, TRT=00:42)
Explanation of term "Blue Moon" (Beatty, TRT=00:44)
Sky & Telescope

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