Saturday, September 19, 2015

The Magnificent Moon - Part 1

July's full moon, with clouds dancing across the sky.

The Magnificent Moon

This is a special time for astronomy buffs. It began in July, when we had an extra full moon in the summer season - two full moons in the month of July.  The first was at the beginning of the month (July 2nd) and the second occurred on July 31st.

This rare phenomenon, called a "Blue Moon" happens every once in a ... blue moon.  We last saw a blue moon in August 2012.   It occurs every three to four years and it happens when there are four full moons in a season. 

Because the lunar cycle is 29.5 days in length, when there is a "blue moon", typically there will be two full moons in a given calendar month: the first full moon early in the month, usually on the first or second day of the month, with the next full moon occurring on or before the last date of the same calendar month. This latter definition, popularizing by a 1946 article in Sky and Telescope magazine, was officially corrected in 1999 to reflect the association of a Blue Moon with a season.
We are also in the period of the Supermoons.  Supermoons happen when a full moon is at its closest point to the Earth during the full moon phase, making it appear unusually large. Last summer we saw several spectacular Supermoons.  Although August's Supermoon was impressive, the next Supermoon, which occurs on September 27th, is going to be beyond spectacular since it will also feature a total lunar eclipse. 

Full Moons and Their Names  

Many cultures, including the Chinese, Celtic, Old English, and Native American tribes have given names to each monthly full moon.  Moon phases and cycles allowed early cultures to keep track of the seasons and they served as a calendar of sorts.  

The best known names for the monthly full moons originated with the Algonquin tribes who lived in New England and westward through New York to Lake Superior. The European settlers adopted the Native American habit of naming the moons and invented some of their own names, all of which have been passed down through subsequent generations.

Every full moon had many names, depending on the culture and North American Indian tribe, but the following list are some of the most common.  

January:  Wolf Moon

The January full moon was named for the
howling of wolves that can be heard echoing in the cold winter air.  Some tribes also referred to the January full moon as the Snow Moon. 

February:  Snow Moon, Hunger Moon

The February full moon was most popularly called the Snow Moon.  A few tribes referred to the January moon by this name but historically, the winter snow fall peaked in February, accounting for the name.  Another common name, the Hunger Moon, referred to the very difficult hunting conditions that resulted from harsh weather and the decreased population of animals that were a source of food during the long winter and which became more scarce by the end of the season.   

March:  Worm Moon, Sap Moon, Lenten Moon

The March snow melt softened the ground revealing earthworm activity, an early and important sign of spring.  In New England especially, the running of the sap in the maple trees gave rise to the name the Sap Moon. Early Christian settlers often referred to it as the Lenten Moon, since the last moon of winter generally preceded Easter.

April: The Pink Moon, Egg Moon, Fish Moon, Sprouting Grass Moon

Among the first spring flowers to appear are the pink wild ground phlox which cover the meadows and fields in early April, hence the name, the Pink Moon.  Other common names reflected other early signs of spring.  Birds built nests and began to lay eggs (the Egg Moon), fish woke from hibernation and began to procreate as well (the Fish Moon), and the greening of pastures was welcomed with the name the Sprouting Grass Moon. 

May:   Flower Moon, Corn Planting Moon, Milk Moon

Prolific spring blooms are credited for the most popular name for May’s full moon, the Flower Moon.  Corn was planted in May (Corn Planting Moon), and spring calves meant more cows producing milk for the first time (Milk Moon).  

June:  Strawberry Moon, Rose Moon

Strawberry crops peak mid-June and the Strawberry Moon is one of the few moons that is virtually universal among most cultures and tribes in North America and Europe. However, more recently it is also referred to as the Rose Moon since rose blooming peaks this month as well in the Northern Hemisphere.

July:  Buck Moon, Thunder Moon

The Buck Moon gets its name from the velvety antlers that buck deer begin growing in July.  In New England, frequent late afternoon thunderstorms made the name the Thunder Moon popular. 

August: The Sturgeon Moon, Grain Moon, Red Moon

The Sturgeon Moon takes its name from the freshwater sturgeon, an important food fish that was in season in the month of August. The hazy August skies often resulted in a reddish tinge to the moon, prompting the name, the Red Moon.  And summer grain harvests are reflected in the name the Grain Moon.

September:  Harvest Moon

Although many vegetable and grain harvests occur earlier in the summer, most of the staple foods and those foods such as root vegetables which were stored for winter use were harvested in September.   The Harvest Moon had a practical value as well.  With the days becoming shorter and shorter, the Harvest Moon enabled farmers to work late into the evening harvesting crops.  The name Harvest Moon relied less on the calendar and more on the timing of the autumn equinox, which occasionally falls in October.   

October:  Hunter's Moon

After a summer of grazing and feeding, deer, pheasant, partridge, and another wild game are ready for hunting and eating. The fall hunting season inspired the name for the Hunter’s Moon. 

November:  Beaver Moon

The Beaver Moon was so named for the beavers who would be trapped for their furs which provided warmth during the cold New England winters.

December:  Cold Moon, Long Night Moon

The long cold winter nights inspired names for the December full moon.  The Cold Moon no doubt speaks to the cold December nights and the winter solstice, which is the longest night of the year, lends its name to the Long Night Moon.

The Phases of the Moon


As the Moon orbits around the Earth, part or all of it is blocked from our view by its relative position to both the Earth and the Sun.   One half of the Moon -- the side facing the Sun -- is always illuminated by the Sun.  The light we see is not generated by the Moon; it is the Sun's light reflecting off the Moon. 

The part of the Moon that is in shadow during the phases of the Moon is the portion of the Moon that is not illuminated by the Sun.  The Moon is not being shadowed by the Earth.  That only happens during a Lunar Eclipse, when the Moon passes through the Earth's shadow.  [That will be explained more fully in The Magnificent Earth - Part 2.]

When we view the Moon, we are seeing the Moon from an angle that forms between the Earth, Moon and Sun as the Moon revolves around the Earth.  Although the side of the Moon facing the Sun is always illuminated, if we are positioned parallel to the Moon, for example, we will only see the half of the illuminated side of the Moon facing us.  That is a Quarter Moon.

When the Earth, Moon and Sun are in a straight line, we either see all of the Moon or none of the Moon.  If the Moon is between the Earth and the Sun, we see none of the illuminated side of the Moon - which ias .  That is the "New Moon".  

At the time of the New Moon, the Moon is between the Earth and the Sun and it rises and sets with the Sun and it's path across the sky during the day is obscured by the Sun's glare.  Most months, the Earth, Moon, and Sky are not lined up in a perfect line;  if they were, we would have a Solar Eclipse.  In fact, that rarely happens, and even when it does, it is only visible at certain points on the Earth.  For a Solar Eclipse to occur, the line-up has to be exact and totality occurs only along a very narrow plane.  

The Moon's orbit is elliptic in shape and tilted with respect to the Earth's. Because of the elliptic shape of the Moon's orbit, even when the Moon is between the Earth and Sun, it is rarely close enough to the Earth to be large enough to fully block the Sun and place the Earth in shadow.  More often than not, at the New Moon, the Moon is in close proximity to the Sun but instead of obscuring the view of the Sun, the Sun's brilliance obscures our view of the Moon.

This is the best time of the month to sky watch and to look for different celestial features.  Without the Moon's light, reflected from the Sun, you can see the sky in greater detail.  Meteor showers that occur during the New Moon or Waxing or Waning Crescents are much more dramatic than those that occur during the Full Moon, when the light from the Moon can make it difficult to see all but the brightest shooting stars.

Image credit:
As the Moon proceeds through it's orbit around the Earth, more of the illuminated side is revealed as the Waxing Crescent.  The Waxing Crescent is the sliver of the right side of the Moon that gradually increases in the days following the New Moon.  Each night, the left edge gradually gets larger until the entire Moon is revealed at the Full Moon. 

At the quarter point, the First Quarter shows the Moon as a semicircle extending from that right side of the Moon.  Between the First Quarter and the Full Moon, we see more of the Moon revealed along that left edge and as it bulges into something akin to an oval, that phase is referred to as the Gibbous Moon, or Waxing Gibbous,

If you are looking at the Moon through a telescope,  the best time and place to look at the landmarks on the moon is along the edge of the shadow, where the craters and other landmarks are heavily shadowed and stand out dramatically.  

Especially at the time of the Gibbous moons, you can see many of the landmarks very clearly.  

L: First Quarter (Credit:    R: Waxing Gibbous (Credit:

July, 2015, American Canyon, CA

The Full Moon occurs when the Earth is between the Moon and the Sun, with the Sun fully illuminating the visible surface of the Moon.  The alignment is approximate; if they are in an essentially parallel line, we have a Lunar Eclipse.  [The next Lunar Eclipse will occur on September 27th and will be discussed in the next post, The Magnificent Moon - Part 2.]  

Just as with the New Moon, the line up is skewed enough (actually, by about 180 degrees) due to the Moon's elliptical orbit so that the side of the Moon facing the Sun appears to be fully illuminated by sunlight and visible to us on Earth.  So even when we are seeing a Full Moon, the Moon that we see is not entirely round, although it appears that way to us on Earth.
We actually see only about half of the truly full moons in the Northern Hemisphere, since the other half are below the horizon at night.  But for several days on either side of the nearly "Full Moon", the reflected sunlight from the moon provides an adequate source of light for people to navigate and work outside, often with minimal or no other illumination.  

Photo Credit:
Following the Full Moon, in the waning phase of the Moon, the Moon follows the same sequence it did in the waxing phase, but in reverse order, of course.  The  Full Moon evolves into the Waning Gibbous and about a week later, we see the Third Quarter or Last Quarter Moon, and the Waxing Crescent.  As the Moon waxes, it waxes in the opposite direction of the waning Moon.  The left side of the Moon remains fully illuminated and the shadow forms and increases from the right side.

The Waxing Gibbous and Last Quarter moons often rise very late, after midnight, and therefore sets quite late, often after dawn.  It's not unusual to see the Waxing Gibbous and Last Quarter moons in the morning sky.

Waning Gibbous Moon and Last Quarter Moon (Credit: and Waning Crescent (Credit: 

In the next blog post, we'll look at what happens during a Lunar Eclipse, and what to expect when we see the next Total Lunar Eclipse that happens in conjunction with September's Supermoon in a little over a week from now.


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