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A total lunar eclipse gives the full moon a reddish tinge in 2015. (GeekWire Photo / Kevin Lisota)

Geographically speaking, the Pacific Northwest is one of the best places in America to see tonight’s super-hyped total lunar eclipse. Meteorologically speaking? Not so much.

Seattleites might have to go as far east as Ellensburg to get a clear view of what’s touted as a “super blue blood moon.” And in reality, the moon won’t be bloody, or blue, or even all that super.

Before we go into full sour-grapes mode, let’s acknowledge that if there’s a chance of seeing the full moon fade to red between 4:51 a.m. and 6:07 a.m. PT Wednesday, it’s definitely worth getting out of bed.

“Set your alarm early and go out and take a look,” NASA’s Gordon Johnson says in the space agency’s preview of the eclipse.

Lunar eclipse visibility
This map shows which phases of the Jan. 31 eclipse will be visible from which parts of the world. The penumbra is a faint, ill-defined shadow on the moon, while the umbra is a darker, well-defined shadow. Click on the image for a larger version. (Sky & Telescope Graphic)

A total lunar eclipse occurs when the moon lines up in its orbit around Earth so that our planet totally blocks out the sunlight falling directly on the lunar disk. The moon turns blood-red — or more accurately, a sunset shade of red or brown — thanks to the sunlight that’s refracted as it passes through Earth’s atmosphere.

Unlike a total solar eclipse, which is visible only along a narrow track of our planet’s surface, a total lunar eclipse is visible from half of the Earth at once, weather permitting. It’s also totally safe to look at the moon during every phase of the eclipse.

Because of the timing, this week’s eclipse can be seen from start to finish if you’re in western North America, the Pacific or east Asia. The northwest U.S. should be able to catch all of the good part, including the partial umbral phase that starts at 3:48 a.m. and ends at 7:11 a.m. PT, with totality in the middle.

Unfortunately, the emphasis here is on “should”: The weather forecast calls for heavy cloud cover overnight west of the Cascades. (Check for sky cover updates.)

This National Weather Service chart shows the sky cover forecast for 5 a.m. PT Jan 31. Grayer shades indicate a higher percentage of cloud cover, bluer shades indicate a lower percentage. Seattle is listed as having 88 percent cloud cover. ( Graphic)

What makes this eclipse so special? A lunar eclipse of any kind occurs two to four times a year, and we’re beginning a string of total eclipses that continues with occurrences on July 27 and on Jan. 21, 2019.

The “super” part of this eclipse comes from the fact that the moon looks roughly 7 percent larger and 14 percent brighter than average, thanks to its relatively proximity to Earth at the time of the eclipse. Most folks won’t notice the difference, however. In fact, this “supermoon” isn’t quite as big as the full moon of Jan. 1.

The “blue” label recognizes that this is the second full moon in a calendar month. That’s the currently accepted astronomical definition for a “blue moon,” the folk-wisdom standard for a rare event (which happens once in a blue moon).

If you combine the eclipse, the moon’s larger-than-average size, and the calendrical coincidence of a blue moon, you could argue that a super blue blood moon is a rare event. The last time that celestial trifecta paid off was in 1982 (for Europe, Africa and western Asia). If you’re looking for a trifecta eclipse that was visible from North America, you have to go back to 1866.

As explained in Sky & Telescope, that’s the basis of the claim that it’s been more than 150 years since we’ve seen a super blue blood moon eclipse. The rarity isn’t anything you’d be able to see by watching the moon. Rather, it comes from combining three features that, by themselves, aren’t all that rare.

All that being said, a lunar eclipse is well worth seeing. And even if it’s a washout in your locale, you can still catch the show online:

If you’re inclined to stay in bed, take solace in knowing that most of these webcasts will be archived for on-demand watching. We’ll round up the highlights on Wednesday morning.

Update for 3 p.m. PT Jan. 30: Via email, University of Washington astronomer Julie Lutz weighed in with her perspective on the super blue blood moon:

“Sounds like an opportunity for vampires! All the adjectives are appropriate. At the time of the January 31 eclipse the full moon will be closer to earth than average. The distance of the moon from earth varies from about 363,000 to 405,000 kilometers, but I can’t tell a difference with my naked eye between these two circumstances. The ‘blue moon’ is simply the second full moon that occurs in a calendar month. Blue moons occur irregularly but over time it averages out to having a blue moon about once every 2.7 years. To me, ‘once in a blue moon’ doesn’t seem all that rare.

“As for the scary-sounding blood moon, during all total lunar eclipses the moon appears somewhat red or orange. This is due to sunlight refracted off of molecules in the Earth’s atmosphere that are then directed to illuminate the moon a bit even though it is passing through the dark part of the earth’s shadow. If the Earth didn’t have an atmosphere, the moon would be essentially invisible during the total phase. So it’s going to be a nice lunar eclipse, but nothing radically different from the others I have viewed over the years (starting at age 9).

“Total lunar eclipses are fun to watch because the much-dimmed moon looks so eerie. Also, they last a while. On average it takes the moon about an hour to move into the Earth’s dark shadow, about an hour to move through it and about an hour to emerge. Incidentally, the next opportunity to view a total lunar eclipse in the Northwest will be January 21, 2019. That eclipse will be available to viewers throughout North America.”

Here’s hoping the weather outlook is better in 2019!

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