The Lowdown on September’s Harvest Moon

The Full Moon of August 18, 2016 - the “Sturgeon Moon” - rising amid cloud over a wheatfield. This is a 5-exposure stack blended with luminosity masks, and shot with the Canon 60Da and 135mm telephoto.
The Full Moon of August 18, 2016 rises amid cloud over a wheat field. Friday night will see the rising of the annual Harvest Moon. Credit: Alan Dyer

It’s that wonderful time of year again when the Harvest Moon teeters on the horizon at sunset. You can watch the big orange globe rise on Friday (Sept. 16) from your home or favorite open vista just as soon as the Sun goes down. Despite being one of the most common sky events, a Full Moon rise still touches our hearts and minds every time. No matter how long I live, there will never be enough of them.

Friday night's Harvest Moon rises around sunset in the faint constellation Pisces the fish. Two fists above and left of the Moon, look for the four stars that outline the massive asterism of Pegasus the flying horse. Stellarium
Friday night’s Harvest Moon rises around sunset in the faint constellation Pisces the fish. Watch for it to come up almost due east around the time of sunset. Once the sky gets dark, look two fists above and left of the Moon for the four stars that outline the spacious asterism of Pegasus the flying horse. Stellarium

To see a moonrise, the most important information you need is the time the moon pops up for your city, which you’ll find by using this Moonrise and Moonset calculator. Once you know when our neighborly night light rises, pre-arrange a spot you can walk or drive to 10-15 minutes beforehand. The waiting is fun. Who will see it first? I’ll often expect to see the Moon at a certain point along the horizon then be surprised it’s over there.

A photographer finds just the right spot in Duluth along Lake Superior to photograph the Full Moon rise. The flattened shape of the Moon is caused by the layer of denser air closer to the horizon refracting or bending the bottom half of the Moon more strongly than the thinner air n
A photographer finds just the right spot in Duluth along Lake Superior to photograph a rising Full Moon. The flattened shape of the Moon is caused by the layer of denser air closer to the horizon refracting or bending the bottom half of the Moon more strongly than the thinner air along the top limb. In effect, refraction “lifts” the bottom half of the Moon upward into the top to give it a squashed appearance. Once the Moon rises high enough so we see it through much thinner (less dense) air, refraction becomes negligible and the Moon assumes its more familiar circular shape.  Credit: Bob King

Depending on how low to the horizon you can see, it’s possible, especially over water, to catch the first glimpse of lunar limb breaching the horizon. This still can be a tricky feat because the Moon is pale, and when it rises, shows little contrast against the still-bright sky. Since the Moon moves about one outstretched fist to the east (left in the northern hemisphere) each night, if you wait until one night after full phase, the Moon will rise in a much darker sky and appear in more dramatic contrast against the sky background.

As the Moon rises, we peer through hundreds of miles of the lower atmosphere, where the air is densest and dustiest. Aerosols scatter much of the blues and greens in moonlight away, leaving orange and red. Turbulence and varying air densities along the line of sight can create all manner of distortions of the lunar disk. This photo sequence showing an extraordinary moonset was taken from the shores of Garrison Lake in Port Orford, Oregon. The camera was facing west; looking across the lake, beyond the narrow foredune and out toward the Pacific Ocean. A very clear atmosphere enabled me to watch the Moon set all the way down to the horizon. The distortion that occurred as it descended was quite remarkable -- the Moon's shape was changing as fast as I could snap a picture.  Credit: Randy Scholten
This photo sequence showing an extraordinary moonset taken from the shores of Garrison Lake in Port Orford, Oregon. “The distortion that occurred as it descended was quite remarkable — the Moon’s shape was changing as fast as I could snap a picture,” said photographer Randy Scholten. As the Moon rises, we peer through hundreds of miles of the lower atmosphere, where the air is densest and dustiest. Aerosols scatter much of the blues and greens in moonlight away, leaving orange and red. Turbulence and varying air densities along the line of sight can create all manner of distortions of the lunar disk. Credit: Randy Scholten

Look closely at the rising Moon with both naked eye and binoculars and you might just see a bit of atmospheric sorcery at work. Refraction, illustrated the icy moonrise image above, is the big one. It creates the squashed Moon shape. But more subtle things are happening that depend on how turbulent or calm the air is along your line of sight to our satellite.

Clouds add their own beauty and mystery to the rising Moon. Credit: Bob King
Clouds add their own beauty and mystery to the rising Moon. Credit: Bob King

Rippling waves “sizzling” around the lunar circumference can be striking in binoculars though the effect is quite subtle with the naked eye. Much easier to see without any optical aid are the weird shapes the Moon can assume depending upon the state of the atmosphere. It can looked stretched out like a hot air balloon, choppy with a step-like outline around its bottom or top, square, split into two moons or even resemble a “mushroom cloud”.

If you make a point to watch moonrises regularly, you’ll become acquainted as much with Earth’s atmosphere as with the alien beauty of our sole satellite.

This Full Moon is special in at least two ways. First, it will undergo a penumbral eclipse for skywatchers across eastern Europe, Africa, Asia and Australia. Observers there should watch a dusky gray shading over the upper or northern half of the Moon around the time of maximum eclipse. The link will take you to Dave Dickinson’s excellent article that appeared earlier here at Universe Today.

The angle of the moon’s path to the horizon makes all the difference in moonrise times. At full phase in spring, the path tilts steeply southward, delaying successive moonrises by over an hour. In September, the moon’s path is nearly parallel to the horizon with successive moonrises just 20+ minutes apart. Times are shown for the Duluth, Minn. region. Illustration: Bob King
The angle of the moon’s path to the horizon makes all the difference in moonrise times. At full phase in spring, the path tilts steeply southward, delaying successive moonrises by over an hour. In September, the moon’s path is nearly parallel to the horizon with successive moonrises just 20+ minutes apart. Times shown are for illustration only  — so you can see the dramatic different in rise times — and don’t refer necessarily to Friday night’s moonrise. Illustration: Bob King

In the northern hemisphere, September’s Full Moon is named the Harvest Moon, defined as the Full Moon closest to the autumnal equinox, which occurs at 9:21 a.m. CDT (14:21 UT) on the 22nd. Normally, the Moon rises on average about 50 minutes later each night as it moves eastward along its orbit. But at Harvest Moon, successive moonrises are separated by a half-hour or less as viewed from mid-northern latitudes. The short gap of time between between bright risings gave farmers in the days before electricity extra light to harvest their crops, hence the name.

Use your imagination and you can see any of several figures in the Full Moon composed of contrasting maria and highlands.
Use your imagination and you can see any of several figures in the Full Moon composed of contrasting maria and highlands.

Why the faster-than-usual moonrises? Every September, the Full Moon’s nightly travels occur at a shallow angle to the horizon; as the moon scoots eastward, it’s also moving northward this time of year as shown in the illustration above. The northern and eastward motions combine to make the Moon’s path nearly level to the horizon. For several nights in a row, it only takes a half-hour for the Earth’s rotation to carry the Moon up from below the horizon. In spring, the angle is steep because the Moon is then moving quickly southward along or near the ecliptic, the path it takes around the sky.  Rising times can exceed an hour.

As you gaze at the Moon over the next several nights, take in the contrast between its ancient crust, called the lunar highlands, and the darker seas (also known as maria, pronounced MAH-ree-uh). The crust appears white because it’s rich in calcium and aluminum, while the maria are slightly more recent basaltic lava flows rich in iron, which lends them a darker tone. Thanks to these two different types of terrain it’s easy to picture a male or female face or rabbit or anything your imagination desires.

Happy moongazing!

DSCOVR Captures EPIC Views of the March 2016 Eclipse

On March 8, 2016 (March 9 local time) the Moon briefly blocked the light from the Sun in what was the only total solar eclipse of the year. The event was visible across portions of southeast Asia, Indonesia, and Micronesia, and was observed by both skywatchers on the ground in person and those watching live online around the world. While to most the view was of a silhouetted Moon slowly carving away the disk of the Sun before totality revealed a shimmering corona, the view from space looking back at Earth showed the Moon’s dark shadow passing over islands, clouds, and sea.

Continue reading “DSCOVR Captures EPIC Views of the March 2016 Eclipse”

Why Aren’t There Eclipses Every Month?

If the Sun, Earth and Moon are lined up, shouldn’t we get a lunar and solar eclipse every month? Clearly, we don’t, but why not?

Coincidences happen all the time. Right, Universe? One of the most amazing is that Moon and the Sun appear to be almost exactly the same size in the sky and they’re both the size of your pinky fingernail held at arm’s length. These coincidences just keep piling up. Thanks Universe?

There are two kinds of eclipses: solar and lunar. Well, there’s a third kind, but we’d best not think about that.

A solar eclipse occurs when the Moon passes in between the Earth and Sun, casting a shadow down on the surface of our planet. If you’re in the path of the shadow, the Moon destroys the Sun. No, wait, I mean the Moon blocks the Sun briefly.

A lunar eclipse happens when the Moon passes through the Earth’s shadow. We see one limb of the Moon darken until the entire thing is in shadow.

You’ve got the Sun, Earth and Moon all in a line. Where they’re like this, it’s a solar eclipse, and when they’re like this, it’s a lunar eclipse.

If the Moon takes about a month to orbit the Earth, shouldn’t we get an eclipse every two weeks? First a solar eclipse, and then two weeks later, lunar eclipse, back and forth? And occasionally a total one of the heart? But we don’t get them every month, in fact, it can take months and months between eclipses of any kind.

If the Sun, Earth and Moon were truly lined up perfect, this would be the case. But the reality is that they’re not lined up. The Moon is actually on an inclined plane to the Earth.

The geometry that creates a total lunar eclipse. Credit: NASA
The geometry that creates a total lunar eclipse. Credit: NASA

Imagine the Solar System is a flat disk, like a DVD. You kids still know what those are, right? This is the plane of the ecliptic, and all of the planets are arranged in that disk.

But the Moon is on another disk, which is inclined at an angle of 5.14 degrees. So, if you follow the orbit of the Moon as it goes around the Earth, sometimes it’s above the plane of the ecliptic and sometimes it’s below. So the shadow cast by the Moon misses the Earth, or the shadow cast by the Earth misses the Moon.

But other times, the Sun, Moon and Earth are aligned, and we get eclipses. In fact, eclipses tend to come in pairs, with a solar eclipse followed by a lunar eclipse, because everything is nicely aligned.

Wondering why the Moon turns red during a lunar eclipse? It’s the same reason we see red sunsets here on Earth – the atmosphere filters out the green to violet range of the spectrum, letting the red light pass through.

Lunar Eclipse from New Jersey 12-21-2010.  Credit:  Robert Vanderbei
Lunar Eclipse from New Jersey 12-21-2010. Credit: Robert Vanderbei

The Earth’s atmosphere refracts the sunlight so that it’s bent slightly, and can illuminate the Moon during the greatest eclipse. It’s an eerie sight, and well worth hanging around outside to watch it happen. We just had recently had a total lunar eclipse, did you get a chance to see it? Wasn’t it awesome?

Don’t forget about the total solar eclipse that’s going to be happening in August, 2017. It’s going to cross the United States from Oregon to Tennessee and should be perfect viewing for millions of people in North America. We’ve already got our road trip planned out.

Are you planning to see the 2017 eclipse? Tell us your plans in the comments below.

What Color Is the Moon? A Simple Science Project For Sunday Night’s Eclipse

There are many ways to enjoy tomorrow night’s total lunar eclipse. First and foremost is to sit back and take in the slow splendor of the Moon entering and exiting Earth’s colorful shadow. You can also make pictures, observe it in a telescope or participate in a fun science project by eyeballing the Moon’s brightness and color. French astronomer Andre Danjon came up with a five-point scale back in the 1920s to characterize the appearance of the Moon during totality. The Danjon Scale couldn’t be simpler with just five “L values” from 0 to 4:

L=0: Very dark eclipse. Moon almost invisible, especially at mid-totality.
L=1: Dark Eclipse, gray or brownish in coloration. Details distinguishable only with difficulty.
L=2: Deep red or rust-colored eclipse. Very dark central shadow, while outer edge of umbra is relatively bright.
L=3: Brick-red eclipse. Umbral shadow usually has a bright or yellow rim.
L=4: Very bright copper-red or orange eclipse. Umbral shadow has a bluish, very bright rim.

The Danjon Scale is used to estimate the color of the totally eclipsed moon. By making your own estimate, you can contribute to atmospheric and climate change science. Credit: Alexandre Amorim
The Danjon Scale is used to estimate the color of the totally eclipsed moon. By making your own estimate, you can contribute to atmospheric and climate change science. Credit: Alexandre Amorim

The last few lunar eclipses have been bright with L values of 2 and 3. We won’t know how bright totality will be during the September 27-28 eclipse until we get there, but chances are it will be on the bright side. That’s where you come in. Brazilian amateur astronomers Alexandre Amorim and Helio Carvalho have worked together to create a downloadable Danjonmeter to make your own estimate. Just click the link with your cellphone or other device and it will instantly pop up on your screen.

On the night of the eclipse, hold the phone right up next to the moon during mid-eclipse and estimate its “L” value with your naked eye. Send that number and time of observation to Dr. Richard Keen at [email protected] For the sake of consistency with Danjon estimates made before mobile phones took over the planet, also compare the moon’s color with the written descriptions above before sending your final estimate.

Graph showing the change in heating of the ground in fractions of degrees (vertical axis) as affected by volcanic eruptions and greenhouse warming since 1979. The blue shows volcanic cooling, the red shows greenhouse warming. Notice the rising trend in warming after 1996. Credit: Dr. Richard Keen
Graph showing the change in heating of the ground in fractions of degrees (vertical axis) as affected by volcanic eruptions and greenhouse warming since 1979. The blue shows volcanic cooling, the red shows greenhouse warming. Notice the rising trend in warming after 1996. Credit: Dr. Richard Keen

Keen, an emeritus professor at the University of Colorado-Boulder Department of Atmospheric and Oceanic Sciences, has long studied how volcanic eruptions affect both the color of the eclipsed moon and the rate of global warming. Every eclipse presents another opportunity to gauge the current state of the atmosphere and in particular the dustiness of the stratosphere, the layer of air immediately above the ground-hugging troposphere. Much of the sunlight bent into Earth’s shadow cone (umbra) gets filtered through the stratosphere.

Volcanoes like Mt. Pinatubo, which erupted in June 1991 in the Philippines, inject tremendous quantities of ash and sulfur compounds high into the atmosphere, where they can temporarily block the sunlight and cause a global drop in temperature. Credit: USGS
Volcanoes like Mt. Pinatubo, which erupted in June 1991 in the Philippines, inject tremendous quantities of ash and sulfur compounds high into the atmosphere, where they can temporarily block sunlight and cause a global drop in temperature. Credit: USGS

Volcanoes pump sulfur compounds and ash high into the atmosphere and sully the otherwise clean stratosphere with volcanic aerosols. These absorb both light and solar energy, a major reason why eclipses occurring after a major volcanic eruption can be exceptionally dark with L values of “0” and “1”.

The moon was so dark during the December 1982 eclipse that Dr. Keen required a 3-minute-long exposure at ISO 160 to capture it. Credit: RIchard Keen
The moon was so dark during the December 1982 eclipse that Dr. Keen required a 3-minute-long exposure at ISO 160 to capture it. Credit: Richard Keen

One of the darkest in recent times occurred on December 30, 1982 after the spectacular spring eruption of Mexico’s El Chichon that hurled some 7 to 10 million tons of ash into the atmosphere. Sulfurous soot circulated the globe for weeks, absorbing sunlight and warming the stratosphere by 7°F (4°C).

A chromolithograph from the German astronomy magazine "Sirius" compares the dark and featureless lunar disk during the eclipse a year after the eruption of Krakatoa (left) with a bright eclipse four years later, after the volcanic aerosols had settled out of the stratosphere (right).
Lithograph from the German astronomy magazine Sirius compares the dark, featureless lunar disk during the 1884 eclipse a year after the eruption of Krakatoa (left) with a bright eclipse four years later, after the volcanic aerosols had settled out of the stratosphere (right).

Meanwhile, less sunlight reaching the Earth’s surface caused the northern hemisphere to cool by 0.4-0.6°C. The moon grew so ashen-black during totality that if you didn’t know where to look, you’d miss it.

Two photos of Earth’s limb or horizon from orbit at sunset before and after the Mt. Pinatubo eruption. The top view shows a relatively clear atmosphere, taken August 30,1984. The bottom photo was taken August 8, 1991, less than two months after the eruption. Two dark layers of aerosols between 12 and 15 miles high make distinct boundaries in the atmosphere. Credit: NASA
Two photos of Earth’s limb or horizon from orbit at sunset before and after the Mt. Pinatubo eruption. The top view shows a relatively clear atmosphere, taken August 30,1984. The bottom photo was taken August 8, 1991, less than two months after the eruption. Two dark layers of aerosols between 12 and 15 miles high make distinct boundaries in the atmosphere. Credit: NASA

Keen’s research focuses on how the clean, relatively dust-free stratosphere of recent years may be related to a rise in the rate of global warming compared to volcano-induced declines prior to 1996. Your simple observation will provide one more data point toward a better understanding of atmospheric processes and how they relate to climate change.

This map shows the Moon during mid-eclipse at 9:48 p.m. CDT. Selected stars are labeled with their magnitudes. Use these stars to help you estimate the Moon's magnitude by looking at the Moon through the backwards through binoculars. Source: Stellarium
This map shows the Moon during mid-eclipse at 9:48 p.m. CDT. Selected stars are labeled with their magnitudes. Examine the Moon backwards through binoculars and find a star it most closely matches to determine its magnitude. If for instance, the Moon looks about halfway in brightness between Hamal and Deneb, then it’s magnitude 1.6. Click to enlarge. Source: Stellarium

If you’d like to do a little more science during the eclipse, Keen suggests examining the moon’s color just after the beginning and before the end of totality to determine an ‘L’ value for the outer umbra.  You can also determine the moon’s overall brightness or magnitude at mid-eclipse by comparing it to stars of known magnitude. The best way to do that is to reduce the moon down to approximately star-size by looking at it through the wrong end of a pair of 7-10x binoculars and compare it to the unreduced naked eye stars. Use this link for details on how it’s done along with the map I’ve created that has key stars and their magnitudes.

The table below includes eclipse events for four different time zones with emphasis on mid-eclipse, the time to make your observation. Good luck on Sunday’s science project and thanks for your participation!

Eclipse Events Eastern Daylight Time (EDT) Central Daylight Time (CDT) Mountain Daylight Time (MDT) Pacific Daylight Time (PDT)
Penumbra first visible 8:45 p.m. 7:45 p.m. 6:45 p.m. 5:45 p.m.
Partial eclipse begins 9:07 p.m. 8:07 p.m. 7:07 p.m. 6:07 p.m.
Total eclipse begins 10:11 p.m. 9:11 p.m. 8:11 p.m. 7:11 p.m.
Mid-eclipse 10:48 p.m. 9:48 p.m. 8:48 p.m. 7:48 p.m.
Total eclipse ends 11:23 p.m. 10:23 p.m. 9:23 p.m. 8:23 p.m.
Partial eclipse ends 12:27 a.m. 11:27 p.m. 10:27 p.m. 9:27 p.m.
Penumbra last visible 12:45 a.m. 11:45 p.m. 10:45 p.m. 9:45 p.m.

Weekly Space Hangout – Sept 18, 2015: Planet Hunter Prof. Sara Seager

Host: Fraser Cain (@fcain)

Special Guests:
Dr. Sara Seager, whose research focuses on computer models of exoplanet atmospheres, interiors, and biosignatures. Her favorite projects involve the search for planets like Earth with signs of life
on them.

Guests:
Paul Sutter (pmsutter.com / @PaulMattSutter)
Morgan Rehnberg (cosmicchatter.org / @MorganRehnberg )
Pamela Gay (cosmoquest.org / @cosmoquestx / @starstryder)

Continue reading “Weekly Space Hangout – Sept 18, 2015: Planet Hunter Prof. Sara Seager”

Eclipse By Fire! Smoky Haze Pervades Night Sky, Darkens Moon

Did you see the Moon last night? I walked outside at 10:30 p.m. and was stunned to see a dark, burnt-orange Full Moon as if September’s eclipse had arrived a month early. Why? Heavy smoke from forest fires in Washington, California and Montana has now spread to cover nearly half the country in a smoky pall, soaking up starlight and muting the moonlight.

If this is what global warming has in store for us, skywatchers will soon have to take a forecast of “clear skies” with a huge grain of salt.

The Pacific Northwest is abundantly dotted with wildfires in Washington, Oregon, Idaho and Montana.This natural-color satellite image was made using the Aqua satellite on August 25, 2015. Actively burning areas, detected by MODIS’s thermal bands, are outlined in red. Credit: NASA image courtesy Jeff Schmaltz, MODIS Rapid Response Team
The Pacific Northwest is abundantly dotted with wildfires in Washington, Oregon, Idaho and Montana in this Aqua satellite image taken on August 25, 2015. Actively burning areas, detected by MODIS’s thermal bands, are outlined in red. Smoke from the fires has been drifting east, blanketing Midwestern skies and blotting out the stars at night. Credit: NASA image courtesy Jeff Schmaltz, MODIS Rapid Response Team

By day, the sky appears the palest of blues. By night, the stars are few if any, and the Moon appears faint, the color of fire and strangely remote. Despite last night’s clear skies, only the star Vega managed to penetrate the gloom. I never saw my shadow even at midnight when the Moon had climbed high into the southern sky.

Last night's Full Moon seen through an 8-inch telescope. The colors are true. Credit: Bob King
Last night’s Full Moon seen through an 8-inch telescope at 11:30 p.m. The colors are true. Credit: Bob King

We’ve seen this smoke before. Back in July, Canadian forest fires wafted south and west and covered much of the northern half of the U.S., giving us red suns in the middle of the afternoon and leaving only enough stars to count with two hands at night. On the bright side, the Moon is fascinating to observe. I set up the telescope last night and spend a half hour watching this unexpected “eclipse”; sunsets appear positively atomic. The size of the smoke particles is just right for filtering out or scattering away blues, greens and even yellow from white light. Vivid reds, pinks and oranges remain to tint anything bright enough to penetrate the haze.

GOES-8 satellite view of the central U.S. taken at 8:15 a.m. CDT August 30, 2015 show a veil of grayish forest fire smoke covering much of the Midwest with clearer conditions to the southeast. The red line is the approximate border between the two. Credit: NOAA
GOES-8 satellite view of the central U.S. taken at 8:15 a.m. CDT August 30, 2015 show a veil of grayish forest fire smoke covering much of the Midwest with clearer conditions to the southeast. The red line is the approximate border between the two. Credit: NOAA

But smoke can cause harm, too. Forest fire smoke contains carbon monoxide, carbon dioxide and soot. On especially smoky days, you can even smell the odor of burning trees in the air at ground level. Some may suffer from burning eyes, asthma or bronchitis on especially smoky days even a thousand miles from the source fires.

Wide-angle view of last night's melon Moon. Notice that the smoke is thicker along the horizontal left and right of the Moon. Above, at a higher elevation, we see through less smoke, so the moonlit sky is a little brighter there. No stars are visible. Credit: Bob King
Wide-angle view of last night’s Moon. Notice that the smoke is thicker along the horizontal – left and right of the Moon. Above, at a higher elevation, we see through less smoke, so the moonlit sky is a bit brighter there. No stars are visible. Credit: Bob King

On clear, blue-sky days, I’ve watched the smoke creep in from the west. It begins a light haze and slowly covers the entire sky in a matter of several hours, often showing a banded structure in the direction of the Sun. A little smoke is OK for observing, but once it’s thick enough to redden the Moon even hours after moonrise, you can forget about using your telescope for stargazing. Sometimes, a passing thunderstorm and cold front clears the sky again. Sometimes not.

The only cures for fire soot are good old-fashioned rain and the colder weather that arrives with fall. In the meantime, many of us will spend our evenings reading about the stars instead of looking at them.

August Full Moon Anticipates September’s Total Lunar Eclipse

Who doesn’t love a Full Moon? Occurring about once a month, they never wear out their welcome. Each one becomes a special event to anticipate. In the summer months, when the Moon rises through the sultry haze, atmosphere and aerosols scatter away so much blue light and green light from its disk, the Moon glows an enticing orange or red.

At Full Moon, we’re also more likely to notice how the denser atmosphere near the horizon squeezes the lunar disk into a crazy hamburger bun shape. It’s caused by atmospheric refraction.  Air closest to the horizon refracts more strongly than air near the top edge of the Moon, in effect “lifting” the bottom of the Moon up into the top. Squished light! We also get to see all the nearside maria or “seas” at full phase, while rayed craters like Tycho and Copernicus come into their full glory, looking for all the world like giant spatters of white paint even to the naked eye.

At full phase, the Moon lies directly opposite the Sun on the other side of Earth. Sunlight hits the Moon square on and fully illuminates the Earth-facing hemisphere. Credit: Bob King
At full phase, the Moon lies directly opposite the Sun on the other side of Earth. Sunlight hits the Moon square on and fully illuminates the Earth-facing hemisphere. Credit: Bob King

Tomorrow night (August 29), the Full Sturgeon Moon rises around sunset across the world. The name comes from the association Great Lakes Indian groups made between the August moon and the best time to catch sturgeon. Next month’s moon is the familiar Harvest Moon; the additional light it provided at this important time of year allowed farmers to harvest into the night.

A Full Moon lies opposite the Sun in the sky exactly like a planet at opposition. Earth is stuck directly between the two orbs. As we look to the west  to watch the Sun go down, the Moon creeps up at our back from the eastern horizon. Full Moon is the only time the Moon faces Sun directly – not off to one side or another – as seen from Earth, so the entire disk is illuminated.

The moon provides the perfect backdrop for watching birds migrate at night. Observers with spotting scopes and small telescopes can watch the show anytime the moon is at or near full. Photo illustration: Bob King
The moon provides the perfect backdrop for watching birds migrate at night. Although a small telescope is best, you might see an occasional bird in binoculars, too. Credit: Bob King

If you’re a moonrise watcher like I am, you’ll want to find a place where you can see all the way down to the eastern horizon tomorrow night. You’ll also need the time of moonrise for your city and a pair of binoculars. Sure, you can watch a moonrise without optical aid perfectly well, but you’ll miss all the cool distortions happening across the lunar disk from air turbulence. Birds have also begun their annual migration south. Don’t be surprised if your glass also shows an occasional winged silhouette zipping over those lunar seas.

Because the Moon's orbit is tilted 5.1 degrees with respect to Earth's, it normally passes above or below Earth's shadow with no eclipse. Only when the lineup is exact, does the Moon then pass directly behind Earth and into its shadow. Credit: Bob King
Because the Moon’s orbit is tilted 5.1° with respect to Earth’s, it normally passes above or below Earth’s shadow with no eclipse — either lunar or solar. Only when the lineup is exact, does the Moon pass directly behind Earth and into its shadow. Credit: Bob King

Next month’s Full Moon is very special. A few times a year, the alignment of Sun, Earth and Moon (in that order) is precise, and the Full Moon dives into Earth’s shadow in total eclipse. That will happen overnight Sunday night-Monday morning September 27-28. This will be the final in the current tetrad of four total lunar eclipses, each spaced about six months apart from the other. I think this one will be the best of the bunch. Why?

The totally eclipsed moon on April 15, 2014 from Duluth, Minn. This was the first in the series of four eclipses called a tetrad. Some refer to this lunar eclipse as a “Blood Moon” because it coincides with the Jewish Passover. Credit: Bob King
The totally eclipsed moon on April 15, 2014 from Duluth, Minn. This was the first in the series of four eclipses called a tetrad. September’s totally eclipsed Moon will appear similar. The coloring comes from sunlight grazing the edge of Earth’s atmosphere and refracted by it into the planet’s shadow. Credit: Bob King
  • Convenient evening viewing hours (CDT times given) for observers in the Americas. Partial eclipse begins at 8:07 p.m., totality lasts from 9:11 – 10:23 p.m. and partial eclipse ends at 11:27 p.m. Those times mean that for many regions, kids can stay up and watch.
  • The Moon passes more centrally through Earth’s shadow than during the last total eclipse. That means a longer totality and possibly more striking color contrasts.
  • September’s will be the last total eclipse visible in the Americas until January 31, 2018. Between now and then, there will be a total of four minor penumbral eclipses and one small partial. Slim pickings.
Diagram showing the details of the upcoming total lunar eclipse. The event begins when the Moon treads into Earth's outer shadow (penumbra) at 7:12 p.m. CDT. Partial phases start at 8:07 and totality at 9:11. Credit: NASA / Fred Espenak
Diagram showing the details of the upcoming total lunar eclipse. The event begins when the Moon treads into Earth’s outer shadow (penumbra) at 7:12 p.m. CDT. Partial phases start at 8:07 and totality at 9:11. Credit: NASA / Fred Espenak

Not only will the Americas enjoy a spectacle, but totality will also be visible from Europe, Africa and parts of Asia. For eastern hemisphere skywatchers, the event will occur during early morning hours of September 28. Universal or UT times for the eclipse are as follows: Partial phase begin at 1:07 a.m., totality from 2:11 – 3:23 a.m. with the end of partial phase at 4:27 a.m.

Eclipse visibility map. Credit: NASA / Fred Espenak
September 27-28, 2015 eclipse visibility map. Credit: NASA / Fred Espenak

We’ll have much more coverage on the upcoming eclipse in future articles here at Universe Today. I hope this brief look will serve to whet your appetite and help you anticipate what promises to be one of the best astronomical events of 2015.

Don’t Blink! April 4th Lunar Eclipse Shortest of the Century

Get ready for one awesome total lunar eclipse early Saturday morning April 4th. For the third time in less than a year, the Moon dips into Earth’s shadow, its dazzling white globe turning sunset red right before your eyes.  All eclipses are not-to-miss events, but Saturday’s totality will be the shortest in a century. Brief but beautiful – just like life. Read on to find out how to make the most of it.

Four total lunars in succession is called a tetrad. During the 21st century there are nine sets of tetrads. Credit: NASA
Four total lunar eclipses in succession with no partials in between is called a tetrad. The April 4th eclipse is part of a tetrad that started last April and will wrap up on September 28. During the 21st century there will be eight sets of tetrads. Credit: NASA

Lunar eclipses don’t usually happen in any particular order. A partial eclipse is followed by a total is followed by a penumbral and so on. Instead, we’re in the middle of a tetrad, four total eclipses in a row with no partials in between. The final one happens on September 28.  Even more remarkable, part or all of them are visible from the U.S. Tetrads will be fairly common in the 21st century with eight in all. We’re lucky — between 1600 and 1900 there were none! For an excellent primer on the topic check out fellow Universe Today writer David Dickinson’s “The Science Behind the Blood Moon Tetrad“.

The Moon moves out of total eclipse and into partial phases during the second of the four tetrad eclipses on October 8, 2015. Credit: Bob King
The partially eclipsed Moon on October 8, 2015.  For skywatchers across the eastern half of North America, this is about how the Moon will appear shortly before it sets. Those living further west will see totality. Credit: Bob King

Lots of people have taken to calling the tetrad eclipses Blood Moons, referring to the coppery color of lunar disk when steeped in Earth’s shadow and the timing of both April events on the Jewish Passover. Me? I prefer Bacon-and-Eggs Moon. For many of us, the eclipse runs right up till sunrise with the Moon setting in bright twilight around 6:30 a.m. What better time to enjoy a celebratory breakfast with friends after packing away your gear?

Map showing where the April 4 lunar eclipse will be penumbral, partial and total. Inset shows a world map. Credit: Larry Koehn / shadowandsubstance.com
Map showing where the April 4 lunar eclipse will be penumbral, partial and total. World map shown in inset. Credit: Larry Koehn / shadowandsubstance.com Inset: Fred Espenak

But seriously, Saturday morning’s eclipse will prove challenging for some. While observers in far western North America, Hawaii, Japan, New Zealand and Australia will witness the entire event, those in the mountain states will see the Moon set while still in totality. Meanwhile, skywatchers in the Midwest and points East will see only the partial phases in a brightening dawn sky. Here are the key times of eclipse events by time zone:

A total lunar eclipse occurs only during Full Moons when the Sun, Earth and Moon form a straight line. The Moon slips directly behind Earth into its shadow. The outer part of the shadow or penumbra is a mix of sunlight and shadow. The inner cone, called the umbra, the Sun is completely blocked from view. However, light refracted by Earth's atmosphere is bent into the umbra where it colors the eclipsed Moon red.
A total lunar eclipse occurs only during full moon phase when the Sun, Earth and Moon lie in a straight line. The Moon slips directly behind Earth into its shadow. The outer part of the shadow or penumbra is a mix of sunlight and shadow and only partially dark. From  the inner shadow, called the umbra, the Sun is completely blocked from view. A small amount of sunlight refracted or bent by Earth’s atmosphere into the umbra, spills into the shadow, coloring the eclipsed Moon red.

Eclipse Events                                     EDT              CDT              MDT             PDT

Penumbra eclipse begins 5:01 a.m. 4:01 a.m. 3:01 a.m. 2:01 a.m.
Partial eclipse begins 6:16 a.m. 5:16 a.m. 4:16 a.m. 3:16 a.m.
Total eclipse begins ——– ——– 5:58 a.m. 4:58 a.m.
Greatest eclipse ——– ——– 6:00 a.m. 5:00 a.m.
Total eclipse ends ——– ——– 6:03 a.m. 5:03 a.m.
Partial eclipse ends ——— ——– ——– 6:45 a.m.
Penumbra eclipse ends ——— ——— ——– ——–

* During the penumbral phase, shading won’t be obvious until ~30 minutes before partial eclipse.

Partial eclipse, when the Moon first enters Earth's dark, inner shadow called the umbra, begins at 5:16 a.m. CDT near the start of morning twilight. Totality begins at 6:58 a.m. with the Moon already set for the eastern half of the country.  Credit: Fred Espenak
Partial eclipse, when the Moon first enters Earth’s dark umbral shadow, begins at 5:16 a.m. CDT near the start of morning twilight. Totality begins at 6:58 a.m. with the Moon already set for the eastern half of the country. Credit: Fred Espenak

This eclipse will also be the shortest total eclipse of the 21st century; our satellite spends just 4 minutes and 43 seconds inside Earth’s umbra or shadow core. That’s only as long as a typical solar eclipse totality. Ah, the irony.

Better have your camera ready or you’ll miss it. The maps below show the maximum amount of the Moon visible shortly before setting from two eastern U.S. cities and the height of the totally eclipsed Moon from two western locations. Click each panel for more details about local circumstances.

The Earth's shadow will take only a small bite out of the Moon before sunrise (6:47 a.m.) as seen from Washington D.C. Source: Stellarium
The Earth’s shadow will take only a small bite out of the Moon before sunrise (6:47 a.m.) as seen from Washington D.C. From all mainland U.S. locations Virgo’s brightest star Spica will appear about 10° to the left of the Moon. Source: Stellarium
Here's the view from Chicago where sunrise occurs at 6:27 a.m. Source: Stellarium
Here’s the view from Chicago where sunrise occurs at 6:27 a.m.  Source: Stellarium
Totality will be visible From Denver, Colorado with the Moon low in the western sky. Source: Stellarium
Totality will be visible From Denver, Colorado with the Moon low in the western sky in morning twilight. Sunrise is 6:42 a.m. Source: Stellarium
Seattle and the West Coast get a great view of totality in a dark sky. The final partial phases will also be visible. Sunrise there is 6:40 a.m. Source: Stellarium
Seattle and the West Coast get a great view of totality in a dark sky. The final partial phases will also be visible. Sunrise there is 6:40 a.m. Source: Stellarium

Now that you know times and shadow coverage, let’s talk about the fun part — what to look for as the event unfolds. You’ll need to find a location in advance with a good view to the southwest as most of the action happens in that direction. Once that detail’s taken care of and assuming clear weather, you can kick back in a folding chair or with your back propped against a hillside and enjoy.

During the early partial phases you may not see the shadowed portion of the Moon with the naked eye. Binoculars and telescopes will show it plainly. But once the Moon's about 50% covered, the reddish-orange tint of the shadowed half becomes obvious. Credit: Jim Schaff
During the early partial phases you may not see the shadowed portion of the Moon with the naked eye. Binoculars and telescopes will show it plainly. But once the Moon is about 50% covered, the reddish-orange tint of the shadowed half becomes obvious. During total eclipse (right), the color is intense.  Credit: Jim Schaff

The entire eclipse can be enjoyed without any optical aid, though I recommend a look through binoculars now and then. The eclipsed Moon appears distinctly three-dimensional with only the slightest magnification, hanging there like an ornament among the stars. The Earth’s shadow appears to advance over the Moon, but the opposite is true; the Moon’s eastward orbital motion carries it deeper and deeper into the umbra.

Nibble by nibble the sunlit Moon falls into shadow. By the time it’s been reduced to half, the shaded portion looks distinctly red even to the naked eye. Notice that the shadow is curved. We live on a spherical planet and spheres cast circular shadows. Seeing the globe of Earth projected against the Moon makes the roundness of our home planet palpable.

Artist view of Earth totally eclipsing the sun as viewed from the moon. Low angled sunlight filtered by our atmosphere is reddened in exactly the same way a setting sun is reddened. That red light bathes the moon’s surface which reflects a bit of it back toward Earth, giving us a red moon during totality.
A simulated view looking back at Earth from the Moon during a total lunar eclipse on Earth. Sunlight grazing Earth’s circumference gets filtered by our atmosphere in exactly the same way the setting or rising Sun looks red. All the cooler colors have been scattered away by air and Red light, bent into the umbra by atmospheric refraction, bathes the lunar surface in red. As you might have guessed, when we see a total lunar eclipse on Earth, lunar inhabitants see a total eclipse of the Sun by Earth. Source: Stellarium

When totality arrives, the entire lunar globe throbs with orange, copper or rusty red. These sumptuous hues originate from sunlight filtered and bent by Earth’s atmosphere into the umbral shadow. Atmospheric particles have removed all the cooler colors, leaving the reds and oranges from a billion sunrises and sunsets occurring around the planet’s circumference. Imagine for a moment standing on the Moon looking back. Above your head would hang the black disk of Earth, nearly four times the size of the Moon in our sky, ringed by a narrow corona of fiery light.

Color varies from one eclipse to the next depending on the amount of water, dust and volcanic ash suspended in Earth’s atmosphere. The December 30, 1982 eclipse was one of the darkest in decades due to a tremendous amount of volcanic dust from the eruption of the Mexican volcano El Chichon earlier that year.

The more particles and haze, the greater the light absorption and darker the Moon. That said, this eclipse should be fairly bright because the Moon does not tread deeply into Earth’s shadow. It’s in for a quick dip of totality and then resumes partial phases.

The Moon's color can vary from yellow-orange to dark, smoky brown during totality depending on the state of the atmosphere. You can also see lots of stars in the sky right up to the Moon's edge when it's in Earth's shadow. This photo from last April's eclipse. Credit: Bob King
The Moon’s color can vary from yellow-orange to dark, smoky brown during totality depending on the state of the atmosphere. You can also see lots of stars in the sky right up to the Moon’s edge when it’s in Earth’s shadow. This photo from last April’s eclipse. Spica is below the Moon and Mars to the right. Credit: Bob King

It’s northern edge, located close to the outer fringe of Earth’s umbra, should appear considerably brighter than the southern, which is closer to the center or darkest part of the umbra.

Earth's shadow exposed! During a lunar eclipse that occurs at dusk or dawn (like  the April 4th one and this one last October) we have the rare opportunity to see Earth's shadow on the distant Moon at the same time it's visible as a dark purple band cast on the upper atmosphere as seen here on October 8, 2015. Credit: Bob King
Earth’s shadow exposed! When a lunar eclipse occurs at dusk or dawn we have the rare opportunity to see Earth’s shadow on the distant Moon at the same time it’s visible as a dark purple band cast on the upper atmosphere as seen here on October 8, 2015. Credit: Bob King

Besides the pleasure of seeing the Moon change color, watch for the sky to darken as totality approaches. Eclipses begin with overwhelming moonlight and washed out, star-poor skies. As the Moon goes into hiding, stars return in a breathtaking way over a strangely eerie landscape. Don’t forget to turn around and admire the glorious summer Milky Way rising in the eastern sky.

Lunar eclipses remind us we live in a Solar System made of these beautiful, moving parts that never fail to inspire awe when we look up to notice.

In case you can’t watch the eclipse from your home due to weather or circumstance, our friends at the Virtual Telescope Project  and SLOOH will stream it online.

Weekly Space Hangout – March 27, 2015: Dark Matter Galaxy “X” with Dr. Sukanya Chakrabarti

Host: Fraser Cain (@fcain)
Special Guest: Dr. Sukanya Chakrabarti, Lead Investigator for team that may have discovered Dark Matter Galaxy “X”.

Guests:
Morgan Rehnberg (cosmicchatter.org / @MorganRehnberg )
Dave Dickinson (@astroguyz / www.astroguyz.com)
Brian Koberlein (@briankoberlein)
Continue reading “Weekly Space Hangout – March 27, 2015: Dark Matter Galaxy “X” with Dr. Sukanya Chakrabarti”