When is the next Blue Moon?

The August 20-21, 2013 full moon will be called a Blue Moon. Wasn’t there a blue moon just last year?

Learn why Blue Moons aren’t so rare anymore.

There are different definitions for Blue Moon. By popular acclaim, the Blue Moon refers to the second of two full moons to occur in the same calendar month. A Blue Moon is also regarded as the third of four full moons in a single season – a season being defined as the time period between a solstice and an equinox, or vice versa. Or, someday, you might see an actual blue-colored moon. The next Blue Moon will fall on August 20-21, 2013. It’ll be a Blue Moon by the seasonal definition, that is, the third of four full moons to take place in a season, in this case between the June 2013 solstice and September equinox. The last Blue Moon by this definition happened on November 21, 2010.

The next Blue Moon by the second-full-moon-in-a-calendar-month definition will be on July 31, 2015. The first full moon of July 2015 will be on July 1, 2015. Previously, the last monthly Blue Moon happened on August 31, 2012.

The term once in a blue moon used to mean something rare. As you can see, now that the rules for naming Blue Moons include so many different possibilities, they’re really pretty common!

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Favorite photos of August 31, 2012 Blue Moon

The August 20-21, 2013 will not be blue in color. This photo was created using special filters. Image via EarthSky Facebook friend Jv Noriega.

 

There’s one kind of blue moon that is still rare, though. It’s very rare that you would see a blue-colored moon, although unusual sky conditions – certain-sized particles of dust or smoke – can create them.

Blue-colored moons aren’t predictable. So don’t be misled by the photo above. The sorts of moons people commonly call Blue Moons aren’t usually blue. For more about truly blue-colored moons, click here.

Now on to folklore’s Blue Moons. Every month typically has a full moon (although sometimes February doesn’t have a full moon at all). In fact, our word for “month” comes from the word “moon.” Most of the time, the names for full moons coincide with particular months or seasons of the year. So whether you define a Blue Moon as the second full moon in a month – or the third full moon of four in a season – the name Blue Moon accounts for times when there are more full moons than is ordinary.

Blue moon as second full moon in a month. In recent decades, many people have begun using the name Blue Moon to describe the second full moon of a calendar month.

The time between one full moon and the next is close to the length of a calendar month. So the only time one month can have two full moons is when the first full moon happens in the first few days of the month. This happens every 2-3 years, so these sorts of Blue Moons come about that often.

When is the next Blue Moon, according to this first definition? July 31, 2015.

Another beautiful image by our friend Jv Noriega – the moon among fast-moving clouds. Will the August 20-21, 2013 be blue in color like this? No. This image was made using blue filters, too. Thank you, Jv!

The idea of a Blue Moon as the second full moon in a month stemmed from the March 1946 issue of Sky and Telescope magazine, which contained an article called “Once in a Blue Moon” by James Hugh Pruett. Pruett was using a 1937 Maine Farmer’s Almanac, but he simplified the definition. He wrote:

Seven times in 19 years there were — and still are — 13 full moons in a year. This gives 11 months with one full moon each and one with two. This second in a month, so I interpret it, was called Blue Moon.

EarthSky’s Deborah Byrd happened upon a copy of this old 1946 issue of Sky and Telescope in the stacks of the Peridier Library at the University of Texas Astronomy Department in the late 1970s. Afterward, she began using the term Blue Moon to describe the second full moon in a calendar month on the radio. Later, this definition of Blue Moon was also popularized by a book for children by Margot McLoon-Basta and Alice Sigel, called “Kids’ World Almanac of Records and Facts,” published in New York by World Almanac Publications, in 1985. The second-full-moon-in-a-month definition was also used in the board game Trivial Pursuit.

Can there be two Blue Moons in a single calendar year? Yes. It last happened in 1999. There were two full moons in January and two full moons in March and no full moon in February. So both January and March had Blue Moons.

The next year of double blue moons is coming up in 2018.

What most call a Blue Moon isn't blue in color. It's only Blue in name. This great moon photo from EarthSky Facebook friend Rebecca Lacey in Cambridge, Idaho. 

Blue moon as third full moon of four in a season. The Maine Farmer’s Almanac defined a Blue Moon as an extra full moon that occurred in a season. One season – winter, spring, fall, summer – typically has three full moons. If a season has four full moons, then the third full moon may be called a Blue Moon.
The next Blue Moon by this definition will fall on August 21, 2013.

In recent years, a controversy has raged – mainly among purists – about which Blue Moon definition is better. The idea of a Blue Moon as the third of four in a season may be older than the idea of a Blue Moon as the second full moon in a month. Is it better? Is one definition right and the other wrong? After all, this is folklore. So the folk get to decide, and, in the 21st century, both sorts of full moons have been called Blue.
As the folklorist Phillip Hiscock wrote in his comprehensive article Folklore of the Blue Moon: Old folklore it is not, but real folklore it is.

So enjoy Blue Moons!

Bottom line: A blue-colored moon is rare. But folklore has defined two different kinds of Blue Moons, and moons that are Blue by name have become pretty common. A Blue Moon can be the second full moon in a month. Or it can be the third of four full moons in a season. The full moon of August 20-21, 2013 will be considered a Blue Moon.

- EarthSky

Sunset: Cape Town

Here are pics from this evening here is Cape Town. The one named MilnertonXXX Is courtesy of Madelein Murphy. Photo taken from Milnerton


SunsetNH01 is taken in Noordhoek

Moonconstantia was taken facing Constantia Berg in a northerly direction. The moon on the top right

All taken around 19h10

- Jakes

A Quiet Interlude in Solar Max

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Something unexpected is happening on the Sun. 2013 was supposed to be the year of “solar maximum,” the peak of the 11-year sunspot cycle. Yet 2013 has arrived and solar activity is relatively low. Sunspot numbers are well below their values from 2011, and strong solar flares have been infrequent. The quiet has led some observers to wonder if forecasters missed the mark.

Solar physicist Dean Pesnell of NASA’s Goddard Space Flight Center has a different explanation. “This is solar maximum,” he says. “But it looks different from what we expected because it is double-peaked.”
Conventional wisdom holds that solar activity swings back and forth like a simple pendulum. At one end of the cycle, there is a quiet time with few sunspots and flares. At the other end, solar max brings high sunspot numbers and frequent solar storms. It’s a regular rhythm that repeats every 11 years.
Reality is more complicated. Astronomers have been counting sunspots for centuries, and they have seen that the solar cycle is not perfectly regular. The back-and-forth swing in sunspot counts can take anywhere from 10 to 13 years to complete. Also, the amplitude of the cycle varies; some solar maxima are very weak, others very strong.

The top image above shows the Earth-facing surface of the Sun on February 28, 2013, as observed by the Helioseismic and Magnetic Imager (HMI) on NASA’s Solar Dynamics Observatory. HMI observes the solar disk at 6173 Ångstroms, a wavelength designed to study surface oscillations and the magnetic field. HMI observed just a few small sunspots on an otherwise clean face, which is usually riddled with many spots during peak solar activity. The video below shows a full solar rotation observed by HMI from February 1-28, 2013. (Download the animation from the links below the image.)

Pesnell notes yet another complication in the solar cycle: “The last two solar maxima, around 1989 and 2001, had not one but two peaks.” Solar activity went up, dipped, then rose again, performing a mini-cycle that lasted about two years. The same thing could be happening now, as sunspot counts jumped in 2011 and dipped in 2012. Pesnell expects them to rebound in 2013: “I am comfortable in saying that another peak will happen in 2013 and possibly last into 2014,”

The second image above plots monthly sunspot numbers for solar cycle 24 (the current one), cycle 23, and cycle 21, the last one with one, normal peak.

Another curiosity of the solar cycle is that the Sun's hemispheres do not always peak at the same time. In the current cycle, the south has been lagging behind the north. The second peak, if it occurs, will likely feature the southern hemisphere playing catch-up, with a surge in activity south of the Sun's equator.

Pesnell is a member of the NOAA/NASA Solar Cycle Prediction Panel, which last assembled in 2008 to forecast the next solar maximum. The panel declared: “The next solar cycle (Cycle 24) will be below average in intensity, with a maximum sunspot number of 90. Given the date of solar minimum and the predicted maximum intensity, solar maximum is now expected to occur in May 2013.”

Given the tepid state of solar activity now, a maximum in May seems unlikely. “We may be seeing what happens when you predict a single amplitude and the Sun responds with a double peak,” says Pesnell. He notes a similarity between Solar Cycle 24 and Solar Cycle 14, which had a double-peak during the first decade of the 20th century. If the two cycles are twins, “it would mean one peak in late 2013 and another in 2015.”

NASA images courtesy Solar Dynamics Observatory and Helioseismic and Magnetic Imager science teams. Sunspot number data from the NOAA National Geophysical Data Center. NASA animation by Robert Simmon. Caption adapted from a story by Tony Phillips, Science@NASA.

Instrument: 

SDO - HMI - NASA

Solar Cycle Update: Twin Peaks?

A new ScienceCast video explores the puzzling behavior of ongoing Solar Cycle 24. Play it

March 1, 2013: Something unexpected is happening on the sun.  2013 is supposed to be the year of Solar Max, the peak of the 11-year sunspot cycle. Yet 2013 has arrived and solar activity is relatively low.  Sunspot numbers are well below their values in 2011, and strong solar flares have been infrequent for many months.

The quiet has led some observers to wonder if forecasters missed the mark. Solar physicist Dean Pesnell of the Goddard Space Flight Center has a different explanation: 
"This is solar maximum," he suggests. "But it looks different from what we expected because it is double peaked."

Conventional wisdom holds that solar activity swings back and forth like a simple pendulum. At one end of the cycle, there is a quiet time with few sunspots and flares. At the other end, Solar Max brings high sunspot numbers and solar storms. It’s a regular rhythm that repeats every 11 years.

Reality, however, is more complicated. Astronomers have been counting sunspots for centuries, and they have seen that the solar cycle is not perfectly regular. For one thing, the back-and-forth swing in sunspot counts can take anywhere from 10 to 13 years to complete; also, the amplitude of the cycle varies. Some solar maxima are very weak, others very strong.

Pesnell notes yet another complication: "The last two solar maxima, around 1989 and 2001, had not one but two peaks." Solar activity went up, dipped, then resumed, performing a mini-cycle that lasted about two years.

The same thing could be happening now. Sunspot counts jumped in 2011, dipped in 2012, and Pesnell expects them to rebound again in 2013: "I am comfortable in saying that another peak will happen in 2013 and possibly last into 2014," he predicts.

Recent sunspot counts fall short of predictions. Credit: Dr. Tony Philips & NOAA/SWPC

Another curiosity of the solar cycle is that the sun's hemispheres do not always peak at the same time. In the current cycle, the south has been lagging behind the north. The second peak, if it occurs, will likely feature the southern hemisphere playing catch-up, with a surge in activity south of the sun's equator.

Pesnell is a leading member of the NOAA/NASA Solar Cycle Prediction Panel, a blue-ribbon group of solar physicists who assembled in 2006 and 2008 to forecast the next Solar Max. At the time, the sun was experiencing its deepest minimum in nearly a hundred years. Sunspot numbers were pegged near zero and x-ray flare activity flat-lined for months at a time. Recognizing that deep minima are often followed by weak maxima, and pulling together many other threads of predictive evidence, the panel issued this statement:

"The Solar Cycle 24 Prediction Panel has reached a consensus. The panel has decided that the next solar cycle (Cycle 24) will be below average in intensity, with a maximum sunspot number of 90. Given the date of solar minimum and the predicted maximum intensity, solar maximum is now expected to occur in May 2013. Note, this is not a unanimous decision, but a supermajority of the panel did agree."

Given the tepid state of solar activity in Feb. 2013, a maximum in May now seems unlikely.

"We may be seeing what happens when you predict a single amplitude and the Sun responds with a double peak," comments Pesnell.

Incidentally, Pesnell notes a similarity between Solar Cycle 24, underway now, and Solar Cycle 14, which had a double-peak during the first decade of the 20th century. If the two cycles are in fact twins, “it would mean one peak in late 2013 and another in 2015.”

No one knows for sure what the sun will do next. It seems likely, though, that the end of 2013 could be a lot livelier than the beginning.


Author: Dr. Tony Phillips | Production editor: Dr. Tony Phillips | Credit: Science@NASA

Photo: Full Moon - Ladysmith, Kwazulu Natal

Sandra Pinto - Moon shining in Ladysmith, KZN

Photos: Weather Observation and Sunset: South Africa (20 February 2013)

GPTrafficGal - 18:45 Greenstone Hill / Edenvale - sky on fire! What a sunset

Shane Bailey - Incredible sunset (picture does not do it justice) over #Atlasville this evening Wed, Feb 20, 2013.

Andrea - Sunset from Greenstone 20/2/2012

Lynette - Spectacular sunset over PTA...The sky on fire!!

 

Graeme Stewart - Sunset over Olivedale #nofilter only in Africa

Julie - Sunset in Germiston.

Annemaяie Andeяson - Most amazing sunset over the Westrand

Shaylene Stenger - #JoziSky over Randburg - breath taking

Bernice van Rooyen - A beautiful sunset tonight in Boksburg.

Sandra Heasman - @SAWDOS1 Stunning sunset over Witbank tonight. God is soooo great!

Nick Roux - Deep pink and red sunset over Midrand tonight

Jaco Ludick - Sasolburg - 20 Februarie 2013

Marida Jooste - Kestell deel met julle, Weste kant vanaand

Photo: SA Weather Observation: Sunrise

Nick Ferreira 43 Air School to share this photo. Sunrise in GFA. (Thanks to Christine Webber, Bathurst for supplying the image)

Video: Golden ring, and dragon tail, from our sun

Our sun is an awesome, life-giving energy machine. Containing more than 99.8% of the total mass of our solar system (Jupiter contains most of the rest, says the great Nine Planets website), it converts about 700,000,000 tons of hydrogen to about 695,000,000 tons of helium every second, via thermonuclear fusion in its interior. In the process, the sun creates about 5,000,000 tons (=3.86e33 ergs) of energy that eventually makes its way to the sun’s surface to be released as the light and warmth that, among other things, sustains all life on Earth. On January 31, 2013, the sun belched energy in two particularly lovely features, both of which were caught on video by NASA’s Solar Dynamics Observatory.

One feature had the shape of the ring, and the other lashed out like a dragon’s tail.

On January 31, 2013, a huge filament of super-hot plasma erupted from the sun. Scientists nicknamed it the Dragon Tail. Image via NASA’s Solar Dynamics Observatory.

This first video shows a variety of views of the break-up of the Dragon Tail filament on January 31, 2013. Solar filaments are not the same as coronal mass ejections, or CMEs (although there was a CME on January 31, too, described below). Filaments are anchored to the sun’s surface in its photosphere – or visible surface – and extend outwards hundreds of kilometers into the sun’s hot outer atmosphere, called the corona. Filaments tend to form over timescales of about a day, and the more stable ones may persist in the corona for several months. The January 31 Dragon Tail filament did not persist, though. The entire event lasted approximately 4 hours, and nothing was released from the sun. The materials in the filament fell back to the sun’s surface due to the pull of gravity.

But there was another event on January 31 that did release material from the sun into space. It was coronal mass ejection (CME), accompanied by an unusual, ring-shaped prominence.

NASA scientists said they did not recall ever seeing this before: a ring-shaped prominence that lay flat above the sun’s surface on January 31, 2013. Image via NASA’s Solar Dynamics Observatory.

On January 31, 2013 at 2:09 EST (6:09 UTC) the sun erupted with an Earth-directed coronal mass ejection (CME). It left the sun at a speed that is about average for CMEs: 575 miles (925 kilometers) per second. It was accompanied by an unusual ring-shaped solar prominence – really, the same thing as a filament, but viewed against a different background – that lay flat above the sun’s surface. On the video, look in the lower left of the sun for the ring-shaped feature. It marks the spot of the CME’s eruption.

When a CME is aimed towards the Earth, it might cause a geomagnetic storm. EarthSky astronomy blogger Christopher Crockett explains this event:

The shock wave of charged particles compresses the Earth’s dayside magnetic field while the nightside gets stretched out. Like an elongated rubber band, the terrestrial magnetic field eventually snaps back with the same amount of energy as a bolt of lightening. The onslaught of charged particles and the temporary restructuring of the Earth’s magnetic field has observable effects. Auroral lights, usually only seen near the poles, can drift to lower latitudes and become more brilliant.

If we see any photos from geomagnetic activity caused by the January 31 CME, we’ll post them here!

- EarthSky

Strong solar radio burst

The weekend solar activity forecast called for "quiet." In fact, says amateur radio astronomer Thomas Ashcraft, "it was really loud. On Saturday, Feb. 2nd, there were several strong solar radio emissions including one super-strong Type III burst at 1954 UT. I captured it at 28 MHz and 21.1 MHz as it totally drowned out a shortwave voice transmission." Click HERE to listen.

The source of the burst was sunspot AR1667, which unleashed a C2.9-class solar flare just before the roar emerged from the loudspeaker of Ashcraft's radio telescope. Type III solar radio bursts are produced by electrons accelerated to high energies (1 to 100 keV) by solar flares. As the electrons stream outward from the sun, they excite plasma oscillations and radio waves in the sun's atmosphere. When these radio waves head in the direction of Earth, they make themselves heard in the loudspeakers of shortwave radios around the dayside of the planet.

More radio bursts could be in the offing. Sunspot AR1667 is crackling with C-class solar flares and seems poised for even stronger M-class eruptions.

- Spaceweather.com

A coronal mass ejection erupts from the sun

On Jan. 31, 2013 at 2:09am EST, the sun erupted with an Earth-directed coronal mass ejection or CME.

On Jan. 31, 2013 at 2:09am EST, the sun erupted with an Earth-directed coronal mass ejection or CME. Experimental NASA research models, based on observations from the Solar Terrestrial Relations Observatory (STEREO) and ESA/NASA’s Solar and Heliospheric Observatory, show that the CME left the sun at speeds of around 575 miles per second, which is a fairly typical speed for CMEs. Historically, CMEs at this speed are mild.

The Solar and Heliospheric Observatory (SOHO) captured these image of a coronal mass ejection (CME), erupting on the left side of the sun early in the morning of Jan 31, 2013, as it was moving away from the sun into space. These images from SOHO are called coronagraphs, in which the bright light of the sun is blocked in order to make the dimmer structures in the sun’s atmosphere, or corona, visible. Credit: ESA&NASA/SOHO

Not to be confused with a solar flare, a CME is a solar phenomenon that can send solar particles into space and reach Earth one to three days later.

The Solar and Heliospheric Observatory (SOHO) captured these image of a coronal mass ejection (CME), erupting on the left side of the sun early in the morning of Jan 31, 2013, as it was moving away from the sun into space. These images from SOHO are called coronagraphs, in which the bright light of the sun is blocked in order to make the dimmer structures in the sun’s atmosphere, or corona, visible. Credit: ESA&NASA/SOHO

Earth-directed CMEs can cause a space weather phenomenon called a geomagnetic storm, which occurs when they connect with the outside of the Earth’s magnetic envelope, the magnetosphere, for an extended period of time. In the past, CME’s such as this have caused auroras near the poles but didn’t disrupt electrical systems on Earth or interfere with GPS or satellite-based communications systems.

EarthSky via NASA

January full moon mimics path of July sun

The January 2013 full moon presents the second full moon after the December 21 solstice. There was a full moon in late December, on December 28. In North America, we often call the second full moon after the winter solstice the Wolf Moon, Hunger Moon or Snow Moon.

The January full moon falls in the wee hours tomorrow (Sunday, January 27) at 4:38 Universal Time. Although the full moon occurs at the same instant worldwide, the clock time (and possibly the date) varies by time zone. For general reference, however, we can say the moon is full all night tonight, lighting up the nighttime from dusk till dawn.

For the mainland U.S. the moon turns full this Saturday evening, January 26. The full moon occurs at 11:38 p.m. Eastern Time, 10:38 p.m. Central Time, 9:38 p.m. Mountain Time and 8:38 p.m. Pacific Time.

Day and night sides of Earth at instant of January 2013 full moon

Day and night sides of Earth at full moon (2013 January 27 at 4:38 Universal Time) Image credit: Earth and Moon Viewer

Elsewhere around the world, the full moon has different clock times. Looking at the worldwide map above, you can see that the full moon comes at midnight in South America and northeastern North America, at sunrise in Africa and at noon in eastern Asia. All these places will see a full-looking moon lighting up the sky tonight from dusk till dawn. But to see the moon at the instant of full moon, the moon has to be above your horizon on the nighttime side of the world.

Photo credit: King Chung Huang

In both the Northern and Southern Hemispheres, the January sun – unlike the January full moon – rises south of due east and sets south of due west. In the Northern Hemisphere, these far-southern risings and settings of the sun give us the short days of winter. South of the equator, the same far-southern sunrises and sunsets bring long summer days. But the full moon lies opposite the sun, mirroring the sun’s place in front of the backdrop stars for six months hence.

And that’s why tonight’s moon – like the July sun – will follow a high path across the sky as seen from the northern part of the globe – and a low path as seen from the southern. This January full moon rises north of due east around sunset, climbs highest in the sky around midnight and sets north of due west around sunrise. Watch the full moon shine from sundown to sunup tonight.

- EarthSky

How often would you see sunrises and sunsets from the moon?

Here on Earth, our planet’s spin on its axis carries us from daylight to darkness and back again every 24 hours. Twenty-four hours is the length of an earthly day. A lot of people incorrectly believe the moon doesn’t rotate, but the moon does spin on its axis, too, just as Earth does. It has to in order to keep one face aimed in our direction. As experienced from a single spot on the moon, there are about 29 earthly days from one lunar noon to the next. That means there would be about two weeks between each lunar sunrise and sunset, from any given spot on Earth’s globe. The video below, from our friend Kurdstan Planetarium in the U.K., shows the sun rising as seen from the moon’s surface and setting two weeks later.

As the video shows, sunrise on the moon would come suddenly. On Earth, when you watch a sunrise or sunset, you can see colored light in the sky, scattered by our planet’s atmosphere. The moon doesn’t have an atmosphere, so there are no twilight colors. Plus, if you were watching a sunrise on the moon, you would see stars rise in the sun’s vicinity and cross the sky with the sun throughout the lunar day. And, because there’s no atmosphere on the moon, sunset on the moon would be equally abrupt. The moment after the sun set would be as dark as midnight, with no lingering color at all.

Earth’s atmosphere also makes our sky look blue in the daytime. From the moon, the sky always looks black, even during the lunar day when the sun is shining in the moon’s sky.

This photo is a classic, taken by Apollo 11 astronauts in 1969. It’s often said to depict an Earthrise as seen from the moon. As seen from any one spot on the moon’s surface, however, the moon doesn’t rise or set. Instead, because one side of the moon always faces Earth, from a given spot on the moon, Earth always hangs in one spot in the lunar sky. See more Apollo 11 images here.

By the way, if you lived on the side of the moon facing Earth, you would see Earth go through phases just as we see moon phases from Earth. Because one side of the moon always faces Earth, from any one spot on the moon, Earth wouldn’t rise or set. It would hang in relatively the same place in the sky as the sun and stars went through their monthly cycle around it.

Bottom line: As seen from a location on the moon, the sun rises and sets in about a monthly cycle. The sun rises – crosses the sky in about two weeks – then sets, bringing on a two-week night for your spot on the moon’s surface.

- EarthSky

When can you see Earth’s shadow?

Just like you or me, Earth casts a shadow. Earth’s shadow extends into space, in the direction opposite the sun. There are several good times to think about and be aware of Earth’s shadow.

See Earth’s shadow any evening, ascending in the east. You can see Earth’s shadow any clear evening ascending in the eastern sky at the same rate that the sun sets below the western horizon. The shadow is a deep blue-grey, and it’s darker than the blue of the twilight sky. The pink band above the shadow is called the Belt of Venus.

Earth’s shadow, with full moon in October 2012. Photo from EarthSky Facebook friend Birgit Boden in northern Sweden.

Earth’s shadow and October 2012 full moon from EarthSky Facebook friend Cattleya Flores Viray in San Diego.

Dark blue Earth’s shadow near the horizon, with an almost full moon in the Belt of Venus above the shadow, in October 2012 as seen by EarthSky Facebook friend Lance Bullion in Baton Rouge, Louisiana.

The shadow of the Earth is big. You might have to turn your head to see the whole thing. And, just so you’ll recognize it more easily, remember that the shadow is curved, in just the same way that the whole Earth is curved.

See Earth’s shadow during an eclipse of the moon. Earth’s shadow extends into space so far that it can touch the moon. That’s what a lunar eclipse is – just the moon within Earth’s shadow.

December 10, 2011 total eclipse of the moon, as seen from Saskatoon, Saskatchewan, Canada. EarthSky Facebook friend Colin Chatfield shot this photo shortly before the total part of the eclipse began.

When the sun, the Earth and the moon are aligned in space (nearly or perfectly), with the Earth in between the sun and moon, then Earth’s shadow falls on the moon’s face. Then people on Earth see the shadow gradually turn a bright full moon dark in an eclipse of the moon. There are typically two or more lunar eclipses every year. Some are total, some are partial, some are a special kind of eclipse known as penumbral. During a lunar eclipse, a very small amount of light from the sun filters through Earth’s atmosphere onto Earth’s shadow on the moon. It’s why – at the middle part of a total lunar eclipse – the shadow on the moon looks reddish.

Night falls when the part of Earth you’re standing on enters Earth’s shadow. Click here to expand this image. Image via NASA

Night is a shadow. The fact is that night on Earth or any other world is a shadow. When night falls, you’re standing within the shadow of Earth.

Bottom line: Check out Earth’s shadow. You might see it as an ascending line of darkness in the east just after sunset. Or you might see it brushing the moon’s face during a lunar eclipse. Or think about night as a shadow, when you’re standing outside in darkness after sunset … maybe tonight.

- EarthSky

Earth closest to sun on January 1-2, 2013

When the New Year brought in the year 2013, our planet Earth was very close to its perihelion – its closest point to the sun for the year. In 2013, Earth comes closest to the sun on Wednesday, January 2 at 5 hours Universal Time (UT). Translating UT to Central Time in the United Sates, perihelion happens last this evening, on Tuesday, January 1, at 11:00 p.m. CST.

The word “perihelion” is from the Greek words peri meaning near, and helios meaning sun.

Earth is closest to the sun every year in early January, when it’s winter for the Northern Hemisphere. We’re farthest away from the sun in early July, during our Northern Hemisphere summer. So you can see that Earth’s distance from the sun isn’t what causes the seasons. On Earth, it’s mostly the tilt of our world’s axis that creates winter and summer. In winter, your part of Earth is tilted away from the sun. In summer, your part of Earth is tilted toward the sun. The day of maximum tilt toward or away from the sun is the December or June solstice.

Earth is about 5 million kilometers – or 3 million miles – closer to the sun in early January than it will be in early July. That’s not a huge change in distance. It’s not enough of a change to cause the seasons on Earth.

Though not responsible for the seasons, Earth’s closest and farthest points to the sun do affect the lengths of the seasons. When the Earth comes closest to the sun for the year, as now, our world is moving fastest in orbit around the sun. Earth is rushing along now at 30.3 kilometers per second (almost 19 miles per second) – moving about a kilometer per second faster than when Earth is farthest from the sun in early July. Thus the Northern Hemisphere winter (Southern Hemisphere summer) is the shortest season as Earth rushes from the winter solstice in December to the March equinox.

In the Northern Hemisphere, the summer season (June solstice to September equinox) lasts nearly 5 days longer than our winter season. And, of course, the corresponding seasons in the Southern Hemisphere are opposite. Southern Hemisphere winter is nearly 5 days longer than Southern Hemisphere summer.

It’s all due to the shape of Earth’s orbit. The shape is an ellipse, like a circle someone sat down on and squashed. The elliptical shape of Earth’s orbit causes the variation in the length of the seasons – and brings our closest point to the sun, in 2013 on January 2, at 5:00 Universal Time.

- EarthSky

Moon Phases Over the Persian Gulf

The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite captured these nighttime views of the Persian Gulf region on September 30, October 5, October 10, and October 15, 2012. The images are from the VIIRS “day-night band,” which detects light in a range of wavelengths from green to near-infrared and uses filtering techniques to observe signals such as gas flares, auroras, wildfires, city lights, and reflected moonlight.

Each image includes an inset of the Moon in four different phases. September 30 shows the Persian Gulf by the light of the full Moon; October 15 shows the effects of a new Moon. As the amount of moonlight decreases, some land surface features become harder to detect, but the lights from cities and ships become more obvious. Urbanization is most apparent along the northeastern coast of Saudi Arabia, in Qatar, and in the United Arab Emirates (UAE). In Qatar and UAE, major highways can even be discerned by nighttime lights.

In eighteenth-century England, a small group of entrepreneurs, inventors and free thinkers—James Watt and Charles Darwin’s grandfathers among them—started a club. They named it the Lunar Society, and the “lunaticks” scheduled their dinner meetings on evenings of the full Moon. The timing wasn’t based on any kind of superstition, it was based on practicality. In the days before electricity, seeing one’s way home after dark was far easier by the light of a full Moon. In the early twenty-first century, electricity has banished the need for such careful scheduling, but the light of the full Moon still makes a difference.

1. References

2. Uglow, J. (2002) The Lunar Men: Five Friends Whose Curiosity Changed the World. New York: Farrar, Straus and Giroux.

NASA Earth Observatory image by Jesse Allen and Robert Simmon, using VIIRS day-night band data from the Suomi National Polar-orbiting Partnership. Suomi NPP is the result of a partnership between NASA, the National Oceanic and Atmospheric Administration, and the Department of Defense. Caption by Michon Scott.

Instrument: 

Suomi NPP - VIIRS - NASA

Last full moon of 2012 on December 27-28

Your calendar probably says tomorrow (Friday, December 28) is the date for the last full moon of 2012. But, for North America, the full moon comes before sunrise tomorrow. So, for us, the moon is closer to full tonight than tomorrow night. Need the exact time of full moon? It’s Friday, December 28 at 10:21 UTC (5:21 a.m. EST, 4:21 a.m. CST, 3:21 a.m. MST and 2:21 a.m. PST). Seeing a bright object in the moon’s vicinity? It’s Jupiter.

Day and night sides of Earth at instant of full moon

Earth’s day and night sides at instant of full moon (2012 December 28 at 10:21 UT). Image credit: Earth and Moon

You might have noticed that the moon was closer to Jupiter yesterday, on December 26, and closer yet on December 25. As always, the moon moves eastward in front of the backdrop stars (and planets) as its orbits our planet Earth. That eastward motion of the moon in orbit causes the moon to moves eastward on our sky’s dome from night to night.

Because this is the closest full moon to the December solstice, this moon carries the name Long Night Moon. That name works for the Northern Hemisphere, where the daylight is fleeting now, while the nighttime is long-lasting. In the Southern Hemisphere – where the days are long and the nights are short – perhaps we could call the closest full moon to the December solstice the Short Night Moon.

Full moon December 27-28, 2012 as seen from Hong Kong by EarthSky Facebook friend Rocco Sung. Thanks Rocco!

The full moon – as always – mimics the sun’s path for some six months hence. Watch tonight as the moon rises around sunset and sets around sunrise tomorrow. Around midnight, the moon climbs highest up for the night, mimicking the position of the noonday June solstice sun.

Given clear skies, tropical and temperate regions from all around the world will see the moon shining from dusk until dawn tonight. In the Northern Hemisphere, the moon’s path across the sky tonight will resemble that of the high-flying summer solstice sun. In the Southern Hemisphere, the moon’s path will follow the low arc of the sun on the winter solstice.

North of the Arctic Circle, there is no sunrise right now because the sun stays below the horizon. But the closest full moon to the December solstice stays out all night long at these far northern latitudes, playacting as the midnight sun of summer.

South of the Antarctic Circle, the sun stays out for 24 hours around the clock. However, the closest full moon to the December solstice simulates the winter sun in the Southern Hemisphere. For that reason, this December full moon won’t rise above the horizon at these far southern latitudes.

The Winter Circle as seen from the Northern Hemisphere

By the way, tonight’s bright and round moon shines right in front of the great big star formation known as the Winter Circle. In the Southern Hemisphere, though, it should really be called the Summer Circle. Either way, tonight’s moon shows you where the sun will reside in front of the background stars six months from now.

Year after year, the Winter Circle shines way high at midnight around the time of the December solstice. However, the presence of the brilliant planet Jupiter near the Winter Circle star Aldebaran is special to this year. You simply can’t miss this dazzling planet, as it’s even brighter than Sirius, the brightest star of the nighttime sky. So let the full moon guide you to Jupiter, the brightest star-like light in the evening sky. Then use Jupiter to find the star Aldebaran and the other bright stars of the Winter Circle.

The Winter Circle as seen from the Southern Hemisphere

Watch tonight, as the Northern Hemisphere’s Long Night Moon (Southern Hemisphere’s Short Night Moon) lights up the nighttime from dusk till dawn!

- EARTHSKY

Sunrise: Warnerbeach

JP Human - Sunrise Warnerbeach (Click on image for larger view.)

NASA Gravity Probes Prepare to Hit the Moon

Dec. 13, 2012: A pair of NASA spacecraft that have been studying the Moon's gravitational field are being prepared for a controlled descent into a mountain near the Moon's north pole. Impact is expected at about 2:28 p.m. PST (5:28 p.m. EST) on Monday, Dec. 17.

"It is going to be difficult to say goodbye to our little robotic twins," says MIT professor Maria Zuber, principal investigator of the Gravity Recovery and Interior Laboratory (GRAIL) mission. "Planetary science has advanced in a major way because of their contributions."

This animation shows the final flight path for NASA’s twin GRAIL probes, which will hit the Moon on Dec. 17, 2012, around 2:28 p.m. PST. Play it

The two probes, named Ebb and Flow, are being sent purposely into the lunar surface because their low orbit and low fuel levels preclude further scientific operations.

Ebb and Flow's successful mission to the Moon has yielded the highest-resolution gravity field map of any celestial body. The map will provide a better understanding not only of the Moon, but also of how Earth and other rocky planets in the solar system formed and evolved.

The spacecraft have been flying in formation around the Moon since Jan. 1, 2012. They were named by elementary school students in Bozeman, Mont., who won a contest.

These 3-D comparisons depict the unnamed lunar mountain targeted by the NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission for controlled impact of the Ebb and Flow spacecraft. Image credit: NASA/JPL-Caltech/MIT/GSFC

The first probe to reach the Moon, Ebb, also will be the first to go down, at 2:28:40 p.m. PST. Flow will follow Ebb about 20 seconds later. Both spacecraft will hit the surface at 3,760 mph (1.7 kilometers per second). No imagery of the impact is expected because the region will be in shadow at the time. The impact site is located near a crater named Goldschmidt.

Ebb and Flow will conduct one final experiment before their mission ends. They will fire their main engines until their propellant tanks are empty to determine precisely the amount of fuel remaining in their tanks. This will help NASA engineers validate fuel consumption computer models to improve predictions of fuel needs for future missions.

"Our lunar twins may be in the twilight of their operational lives, but one thing is for sure, they are going down swinging," said GRAIL project manager David Lehman of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Even during the last half of their last orbit, we are going to do an engineering experiment that could help future missions operate more efficiently."

Because the exact amount of fuel remaining aboard each spacecraft is unknown, mission navigators and engineers designed the depletion burn to allow the probes to descend gradually for several hours and skim the surface of the moon until the elevated terrain of the target mountain gets in their way.

The burn that will change the spacecrafts' orbit is scheduled to take place Friday morning, Dec. 14.

"Such a unique end-of-mission scenario requires extensive and detailed mission planning and navigation," said Lehman. "We've had our share of challenges during this mission and always come through in flying colors, but nobody I know around here has ever flown into a Moon mountain before. It'll be a first for us, that's for sure."


Production editor: Dr. Tony Phillips | Credit: Science@NASA

More Information

During their prime mission, from March through May 2012, Ebb and Flow collected data while orbiting at an average altitude of 34 miles (55 kilometers). Their altitude was lowered to 14 miles (23 kilometers) for their extended mission, which began Aug. 30 and sometimes placed them within a few miles of the moon's tallest surface features.

JPL manages the GRAIL mission for NASA's Science Mission Directorate in Washington. The mission is part of the Discovery Program managed at NASA's Marshall Space Flight Center in Huntsville, Ala. Lockheed Martin Space Systems in Denver built the spacecraft. JPL is a division of the California Institute of Technology in Pasadena.

For more information about GRAIL, visit: http://www.nasa.gov/grail .