Blues for the Second Full Moon of July

An artificially created 'Blue Moon,' using the white balance settings on the camera. Image credit and copyright: John Chumack

Brace yourselves for Blue Moon madness. The month of July 2015 hosts two Full Moons: One on July 2nd and another coming right up this week on Friday, July 31st at 10:43 Universal Time (UT)/6:43 AM EDT.

In modern day vernacular, the occurrence of two Full Moons in one calendar month has become known as a ‘Blue Moon.’ This is a result of the synodic period (the amount of time it takes for the Moon to return to a like phase, in this case Full back to Full) of 29.5 Earth days being less than every calendar month except February.

In the ‘two Full Moons in one month’ sense, the last time a Blue Moon occurred was on August 31st, 2012, and the next is January 31st, 2018. The next time a Blue Moon occurs in the month of July is 2034, and the last July Blue Moon was 2004.

We say “once in a blue Moon,” as if it’s a rarity, but as you can see, they’re fairly frequent, occurring nearly once every 2-3 years or so.

Now, we’ll let you in on a secret. Like its modern internet meme cousin the ‘Super-Moon,’ astronomers don’t sit in mountain top observatories discussing the vagaries of the Blue Moon. In fact, astronomers rarely like to observe during the weeks surrounding the light-polluting Full Moon, and often compile data from the comfort of their university offices rather than visit mountaintop observatories these days…

The modern Blue Moon is now more of a cultural phenomenon. We’ve written previously about how an error brought us to the current ‘two Full Moons in one month definition.’ A more convoluted old timey definition was introduced in ye ole Maine Farmer’s Almanac circa 1930s as “the third Full Moon in an astronomical season with four.”

Legend has it that the Maine Farmer’s Almanac denoted this pesky extra seasonal Full Moon with ‘blue’ instead of black ink… to our knowledge, no examples exist to support this intriguing tale. Anyone have any old almanacs in the attic holding such a revelation out there?

The ghostly glow of the gibbous moon in Jean-Francois Millet's The Sheepfold. Image Credit: Public Domain
The ghostly glow of the gibbous moon in Jean-Francois Millet’s The Sheepfold. Image Credit: Public Domain

We’ve also laid out the occurrences for both types of Blue Moons for the remainder of the decade, as well as its New Moon cousin and internet meme to be, the Black Moon.

The rising waxing gibbous Moon on the night of September 23rd, 1950. Image credit: Stellarium

Of course, the Moon most likely won’t appear to be physically blue, no matter what friends/family/co-workers/anonymous persons on Twitter say. The Moon can actually appear blue, as it did on September 23rd, 1950 for much of the eastern United States and Canada through the haze of several forest fires in western Canada. The Moon was actually at waxing gibbous phase on the evening of this phenomenon, and as far as we can tell, no photographic documentation of this event exists. Spaceweather, has, however gathered a gallery of blue moon eyewitness reports over the years, including a few images. This occurs when moonlight is filtered through suspended oil drops about a micrometer in diameter which scattered yellow and red light, leaving a Moon with a ghostly indigo glow.

Image credit
The 2012 Blue Moon as seen rising from Hudson, Florida. Image credit: Dave Dickinson

So there’s definitely another challenge to catch and photograph a truly ‘Blue Moon’ under such rare atmospheric circumstances… and remember, the Moon doesn’t have to be near Full to do it!

Watch that Moon, as we’ve got a few red letter dates coming up through the remainder of 2015.  First up: the Supermoon season cometh in August, as we have a series of three Full Moons falling less than 24 hours from perigee on August 29th, September 28th, and October 27th. Our money is on that middle one as having the potential to generate the most online lunacy, as it’s also the last  total lunar eclipse of the current tetrad of four total lunar eclipses for 2014 and 2015, a ‘super-blood moon eclipse’ anyone? Though the dead won’t rise from the grave to mark such an occasion, you can be sure that many a sky aficionado will stumble zombie-like into the office the next day after pulling an all-nighter for the last good North American total lunar eclipse until 2018.

And it’s worth noting the path of the Moon, as it reaches its shallow mid-point in the last half of 2015. The Moon’s orbit is tilted about five degrees relative to the ecliptic, meaning that it can ride anywhere from 18 degrees—as it does this year—to 28 degrees from the celestial equator. This cycle takes about 19 years to complete, and a wide-ranging ‘long nights Moon’ last occurred in 2006, and will next occur in 2025.

A 'mock Blue Moon...'
A ‘mock Blue Moon…’ induced by use of a military flashlight filter. Image credit: Dave Dickinson

So don’t fear the Blue Moon, but be sure to take a stroll under its light this coming Friday… and perhaps enjoy a frosty Blue Moon beer on the eve of the sultry month of August.

Super-Moon Monday: The 3rd (& Final?) Act

The gibbous Moon rising rising over the Andes Mountains in Chile. (Credit: @WladimirPulgarG/Flickr).

“Once more into the breach, my dear friends…”

Such a quip may be deemed appropriate as we endured the media onslaught this past weekend for the third and final perigee Full Moon of 2013.

Tonight, on Monday, July 22nd, the Moon reaches Full at 18:15 Universal Time (UT)/4:15 PM EDT. This is only 21.9 hours after reaching perigee, or the closest point in its orbit at 358,401 kilometres from the Earth on the Sunday evening at 20:28 UT. Continue reading “Super-Moon Monday: The 3rd (& Final?) Act”

Was Last Night’s Moon Blue for You?

A blue-tinted Moon on August 31, 2012. Credit (and tinting): joeys-astro-gallery on Flickr

Last night’s full Moon was a “Blue Moon” — where the Moon isn’t really blue, but is the name for when there is a second full Moon in a month. Normally, we only get one full Moon a month, but every 2 1/2 years or so, the calendar lines up just right, since the time between full moons is 29.5 days while most months are 30 or 31 days. Since we had a full Moon on August 2 and a second one last night on August 31,

Of course the Moon has reason to be “blue” (if we want to anthropomorphize a little) with the recent death of the first Moonwalker, Neil Armstrong. And sometimes the Moon can actually appear to be blue if volcanic ash or forest fire ash are in the atmosphere in your location, since ash particles can scatter away all the warm colors in Moonlight, leaving a pale blue tint to the Moon.

Our readers sent in their Blue Moon images from last night, and some, like the one above, used a little image editing magic to make the Moon appear blue, but most are just gorgeous images of our closest neighbor and constant companion in space.

Feast your eyes, below:

Clouds and lighting give the Moon a blue tint, too, in Paris, France. Credit: VegaStarCarpentier on Flick.

The Blue Moon on 08-31-2012, from Dayton, Ohio. Equipment: Modified Canon Rebel Xsi & 6″ F8 Cave reflector Scope, 1200mm, ISO 400 1/640 second exposure. Credit: John Chumack.

A tribute to Neil Armstrong on August 31, 2012 taken the day of his funeral. “The Moon’s own salute to its first great explorer.” Credit: Barry Q. Arnold, Alvaton, Kentucky, USA

The Moon on August 31, 2012 from Uberaba, Curitiba – Paraná, Brazil. Credit: Glauco Hass on Flickr.

The Moon on 31/08/2012 – 23:15 TL – from São Paulo, Brazil. Equipment: Maksutov Cassegrain Vixen 110 mm – F = 1035 mm – F/9.4 – Plano Focal – Nikon D3100 – 1/200 – ISO 100. Credit: Ednilson Oliveira.

August’s Other Full – “Blue” – Moon (on the 31st) as seen from Lowell, Michigan. Credit: Kevin’s Stuff on Flickr.

And here are a few notable images from August 30, the “almost” full Moon:

Great close-up (and not a crop) of the Moon on August 30, 2012 from Kopreinitz Koprivnicko-Krizevacka, Croatia. Credit: Eddie MacGraw on Flickr.

A helicopter by the Moon on August 30, 2012 as seen from London, England. The exhaust heat from the chopper distorts the light from the Moon. Credit: Sculptor Lil on Flickr.

Sugar Loaf, New York – The almost full moon rises behind Sugar Loaf Mountain on August 30, 2012. Credit: Tom Bushey on Flickr.

When are the next Blue Moons?
July 31, 2015
Two in 2018 — January 31 and March 31, meaning there is no February full Moon
October 31, 2020
August 31, 2023
May 31, 2026
December 31, 2028
September 30, 2031

Want to get your astrophoto featured on Universe Today? Join our Flickr group or send us your images by email (this means you’re giving us permission to post them). Please explain what’s in the picture, when you took it, the equipment you used, etc.

Blue Moon This Week

A Blue Moon. Credit:

When you hear someone say “Once in a Blue Moon” you know what they mean. They’re usually talking about something rare, silly, and even absurd. After all, when was the last time you saw the Moon turn blue? Well, rare or not, we’re having one this week, and according to astronomer David Reneke writer and publicist for Australasian Science magazine, a Blue Moon is slated for the last day of this month, Friday, August 31.

It’s not at all clear where the term ‘Blue Moon’ comes from. According to modern folklore it dates back at least 400 years. A Blue Moon is the second Full Moon in a calendar month. “Usually months have only one Full Moon, but occasionally a second one sneaks in, David said. “Ancient cultures around the world considered the second Full Moon to be spiritually significant.”

Full Moons are separated by 29 days, while most months are 30 or 31 days long, so it is possible to fit two Full Moons in a single month. This happens every two and a half years, on average. By the way, February is the only month that can never have a Blue Moon by this definition. We had one Full Moon on August 2 this year and the second will be Friday night.

Does the Blue Moon actually turn blue? No. Physically colored Blue Moons are rare, and that’s where the phrase comes from, “Once in a Blue Moon”. There are occasions though when pollution in the Earth’s atmosphere can make the Moon appear to look blue in color. The extra dust scatters blue light. For example, the Moon appeared bluish green across the entire Earth for about 2 years after the eruption of Krakatoa in 1883.

There were also reports of a blue-green coloured Moon caused by Mt. St. Helens in 1980 and Mount Pinatubo in 1991. “So in a sneaky sort of way, it could be true,” Dave said with a grin. Look up at the night sky on August 31 and see for yourself. Everywhere in the world the full Moon rises in the east just as the Sun is setting in the west.

“Blue Moons don’t have any real significance scientifically but they’re fun to look at,” David said. “Anytime you can get people out to look at the real sky to me is a great plus, enjoy it while you can this Friday night and while you’re looking moonward, think of Neil Armstrong, OK?”

Story Contributed by Dave Reneke. Image Credit: John Chumack.

Weekly SkyWatcher’s Forecast: August 27-September 2, 2012

Greetings, fellow SkyWatchers! If you only get your telescope or binoculars out once in a Blue Moon, then get them out this week when a Blue Moon actually happens! However, if you can’t wait, then let’s explore some great lunar features, bright star clusters and great double stars. When you’re ready to learn some history, mystery and more, then just step on inside…

Monday, August 27 – Tonight the waxing Moon’s most notable features will be the vast area of craters dominating the south-central portion near and along the terminator. Now emerging is Ptolemaeus – just north-northeast of Albategnius. This large round crater is a mountain walled plain filled with lava flow. With the exception of interior crater Ptolemaeus A, binoculars will see it as very smooth. Telescopes, however, can reveal faint mottling in the surface of the crater’s interior, along with a single elongated craterlet to the northeast. Despite its apparent uniformity, close inspection has revealed as many as 195 interior craterlets within Ptolemaeus! Look for a variety of interior ridges and shallow depressions.

With the Moon low to the southwest, we have a chance to go northeast to Cepheus for a new study – NGC 7160 (Right Ascension: 21 : 53.7 (hours : minutes) Declination: +62 : 36). At magnitude 6.1, this small open cluster is easily identified in scopes and may be seen as a faint starfield in binoculars. You’ll find it about a finger-width north of Nu Cephei.

Tuesday, August 28 – In 1789 on this day, Sir William Herschel discovered Saturn’s moon Enceladus.

On the lunar surface tonight, we’ll start by following the southward descent of large crater rings Ptolemaeus, Alphonsus, and Arzachel to a smaller, bright one southwest named Thebit. We’re going to have a look at Hell…

Just west of Thebit and its prominent A crater to the northwest, you see the Straight Wall – Rupes Recta – appearing as a thin, white line. Continue south until you see large, eroded crater Deslandres. On its western shore, is a bright ring that marks the boundary of Hell. While this might seem like an unusual name for a crater, it was named for an astronomer – and clergyman!

Once you’ve been to Hell, let’s go to the heavens for NGC 7235 (Right Ascension: 22 : 12.6 – Declination: +57 : 17). Locate the star crowded area of Epsilon Cephei which will also include this 7.7 magnitude open cluster in the same low power field. Give it a try. Look for a small, rectangular assortment of 10th magnitude and fainter stars, including a beautiful ruby red, west-northwest of Epsilon.

Wednesday, August 29 – Due south of mighty Copernicus on the eastern edge of Mare Cognitum, you will see a ruined pair of flattened craters. They are Bonpland and Parry – with Frau Mauro just above them. The smallest and brightest of these ancient twins is the eastern Parry. Have a look at its south wall where a huge section is entirely lost. It was near this location that Ranger 7 ended its successful flight in 1964. Just south of Parry is another example of a well-worn Class V crater. See if you can distinguish the ruins of Guericke. Not much is left save for a slight U-shape to its battered walls. These are some of the oldest visible features on the Moon!

If you’d like to head for something very young, have a look at 6.8 magnitude open cluster NGC 6811 (Right Ascension: 19 : 37.3 – Declination: +46 : 23) in Cygnus. This mid-sized, unusually dense open cluster is found less than finger-width north-northwest of Delta – the westernmost star of the Northern Cross. Like most open clusters, the age of NGC 6811 is measured in millions, rather than billions, of years. Visible in binoculars on most nights, telescopes should show a half dozen or so broadly-spaced resolvable stars overlaying a fainter field. Be sure to return again on a moonless night, and have another look a disparate double Delta!

Thursday, August 30 – Today celebrates the Yohkoh Mission, launched in 1991. It was a joint effort of both Japan and the United States to monitor solar flares and the corona. While its initial mission was quite successful, on December 14, 2001 the signal was lost during a total eclipse. Unable to reposition the satellite back towards the Sun, the batteries discharged and Yohkoh became inoperable.

While the graceful Gassendi will try to steal the lunar show tonight, let’s have a go at Foucault instead. To find it, head north to Sinus Iridum and locate Bianchini in the Juras Mountains. Just northeast, and near the shore of south-eastern Mare Frigoris, look for a bright little ring.

Physicist Jean Foucault played an instrumental role in the creation of today’s parabolic mirrors. His “Foucault knife edge test” made it possible for opticians to test mirror curves for optical excellence during the final phases of shaping before metallization. Thanks to Foucault’s insight, we can turn our telescopes on such difficult double stars as Beta Delphini and resolve its 0.6 arc-second distant 5.0 magnitude companion. A challenge for smaller scopes is MU Cygni. This 4.5 and 6.0 magnitude pair should be resolvable in any scope that passed Foucault’s test!

Tonight let’s view a double star, Eta Lyra. Just on the edge of unaided visibility, you will find it around three finger-widths due east of Vega. This wide, disparate pair of 4.5 and 8.0 magnitude stars should be resolvable in just about any scope, but is beyond the reach of binoculars.

Friday, August 31 – Tonight we will begin entering the stream of the Andromedid meteor shower, which peaks off and on for the next couple of months. For those of you in the northern hemisphere, look for the lazy “W” of Cassiopeia to the northeast. This is the radiant – or relative point of origin – for this meteor stream. At times, this shower has been known to be spectacular, but let’s stick with an accepted fall rate of around 20 per hour. These are the offspring of Beila’s Comet, one that split apart leaving radically different streams – much like 73/P Schwassman-Wachmann did last year. These meteors have a reputation for red fireballs with spectacular trains, so watch for them in the weeks ahead.

It’s Blue Moon! That doesn’t mean the Moon is going to be colored any differently – it just means it’s the second full Moon within a month.

Think having all this Moon around is the pits? Then let’s venture to Zeta Sagittarii and have a look at Ascella – “The Armpit of the Centaur.” While you’ll find Zeta easily as the southern star in the handle of the teapot formation, what you won’t find is an easy double. With almost identical magnitudes, Ascella is one of the most difficult of all binaries. Discovered by W. C. Winlock in 1867, the components of this pair orbit each other very quickly – in just a little more than 21 years. While they are about 140 light-years away, this gravitationally bound pair waltz no further apart than our own Sun and Uranus!

Too difficult? Then have a look at Nu Sagittarii – Ain al Rami, or the “Eye of the Archer.” It’s one of the earliest known double stars and was recorded by Ptolemy. While Nu 1 and Nu 2 are actually not physically related to one another, they are an easy split in binoculars. Eastern Nu 2 is a K type spectral giant that is around 270 light-years from our solar system. But take a very close look at the western Nu 1 – while it appears almost as bright, this one is 1850 light-years away! As a bonus, power up in the telescope, because this is one very tight triple star system!

Saturday, September 1 – On this day 1859, solar physicist Richard Carrington (who originally assigned sunspot rotation numbers) observed the first solar flare ever recorded. Naturally enough, an intense aurora followed the next day. 120 years later in 1979, Pioneer 11 made history as it flew by Saturn.

While the Moon essentially appears to be full throughout the night, take the time to compare the western and eastern limbs. To the west, you will see the smooth arc no longer displays high contrast features. To the east you should see a broken edge now in sunset. Watch in the days ahead as many of your favorite craters begin to reveal themselves in a “different light.”

Tonight let’s visit Alya. One of the fainter stars to receive a proper name, Theta Serpens Caput is located around a hand span due east of Beta Ophiuchi. Thankfully, resolving this wide, matched magnitude pair is easier than finding it. If you have high power, self-stabilizing binoculars, this one could be real fun!

Sunday, September 2 – It won’t be long until the Moon lights the skies, so let’s have a look at disparate double Kappa Pegasi. It’s the westernmost star of northern Pegasus and is around a hand span due south of Sadr – the central star of the Northern Cross. At magnitude 4.3, look for a faint companion leading the orange-yellow primary across the sky. This one could be tough for small scopes – so make a challenge of it!

Now let’s have a look at Beta and Gamma Lyrae – the lower two stars in the “Harp.” Beta is actually a quick change variable dropping to less than half the brightness of Gamma every 12 days, but for a few days the two stars appear to be of near equal brightness. Beta is a very unusual eclipsing spectroscopic binary. Its unseen companion may be a “collapsar.”
Before you call it a night, head a finger-width north of Omicron Andromedae for 15 Lacertae. Just on the edge of unaided visibility, this carbon star is also a disparate double. The 5.2 magnitude variable primary will appear more red at its faintest, but its 11.0 magnitude companion is the faintest of all!

But don’t put the telescope away just yet. If you can locate the Moon, you can locate Uranus! Just take a look about 3 degrees away to lunar south to catch the slightly greenish orb of the outer planet.

Until next week, ask for the Moon… But keep on reaching for the stars!

Ptolemaeus Crater Image Credit: Damian Peach

What is a Blue Moon?

A Blue Moon. Credit:


A lunar month takes 29.53 days. This is the amount of time it takes for the Moon to complete a cycle through all the phases, from new moon to full moon and then back to new moon again. This is very close to the length of a month in the Western calendar, which usually have 30 or 31 days. Every month usually has one of each of the phases. So a typical month will have a new moon, first quarter, full moon and last quarter moon. But every now and then, a month will have two of the same phases. When a month has two full moons, the second one is called a “blue moon”.

Blue moons are rare, and that’s where the phrase comes from, “once in a blue moon”. How rare? They always happen once every 2-3 years (2.72 years, to be exact). It’s this second moon in the month that’s considered the blue moon.

Does the blue moon actually turn blue? No. A blue moon is exactly the same color as a regular full moon – yellow.

The Moon can turn blue when there’s a certain amount of dust or pollution in the air. The extra dust scatters blue light, making the Moon appear more blue. For example, the Moon appeared blue across the entire Earth for about 2 years after the eruption of Krakatoa in 1883.

Here is a list of upcoming blue moons:

  • 2018: January 2, January 31st
  • 2018: March 2, March 31st
  • 2020: October 1, October 31st


We have an article here on Universe Today about all the phases of the Moon.

Here’s an article from NASA about blue moons.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?