Educator How-to: Learn to Draw a Celtic Triquetra

At the Houston Museum of Natural Science, we know that people are as much a part of natural science as rocks and dinosaurs. That’s why we love social studies and maintain exhibits like the John P. McGovern Hall of the Americas and the Hall of Ancient Egypt. We find the development of societies fascinating!

The historical Celts, a diverse group of tribal societies in Iron Age Europe, ranged over a large swath of land reaching as far west as Ireland and the Iberian Peninsula, east to central Anatolia, and north to Scotland. The Celts used a three-cornered symbol, known as the triquetra, to adorn everyday items and important ritual objects. Similar tri-cornered symbols are seen in the artwork of many ancient civilizations. It is speculated that the symbol illustrates the uniting of the past, present, and future or birth, life, death. As Christianity spread through Europe, the triquetra was used to help new converts to understand the concept of the Trinity.

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It is really simple to draw this ancient knot-work symbol. All you need is paper, a compass, an eraser, and some markers.

First, using a compass, draw a circle of at least 3 inches in diameter in the middle of your paper. Make sure to leave room around the circle, as the resulting knot will be slightly larger than the initial circle. Make sure that you do not adjust the compass after the circle is drawn.

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Next, use a pencil to make a point on the circle at the twelve o’clock position. Then, place the point of the compass on this point and use it to make marks where it crosses the circle on each side.   

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Now, place the point of the compass on one of the marks made in the previous step. It doesn’t matter which one. Then, draw a semi-circle within the initial circle. It should start at the twelve o’clock point and end in the lower quarter of the circle. The arc does not need to be continued outside of the circle. Make another arc, identical to the first one. The two arcs should cross at the center point of the circle. If they don’t, check to make sure that the compass setting has not been changed.

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Then, placing the compass point on the lower tailing end of one of the arcs, mark off another tic on the bottom of the circle.celtic5

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Now place the point of the compass on the bottom mark and draw an additional arc from side to side within the circle.

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You will now need to enlarge the diameter of the compass a bit. Place the compass point back onto the marks made in the upper half of the circle. From each point, draw another arc within the circle, and extending a little beyond its border. It is important to make sure the arcs are extend a bit outside of the circle so they’ll meet up when the arcs are all drawn.

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Pick a point where one of the knot strips intersects another, and make it pass over the other, erasing the lines from the underside from within the “over” strip. The next pass for the knot strip, following the same strand, will be to go under the next intersection, so erase appropriately. At this point ,you may erase the initial circle and the arc marks.

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Now your trisquetra is complete! Color it in! See designs like this and others this summer in the Medieval Madness Xplorations Summer Camp.

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Seeing Stars with James Wooten: The Stars of Summer are Here

The Summer Triangle is high in the east.  This consists of the brightest stars in Cygnus, Lyra, and Aquila.  Scorpius, the Scorpion, is in the south, with the ‘teapot’ of Sagittarius to his left.  Leo, the Lion, sets in the west.  From the Big Dipper’s handle, ‘arc to Arcturus’ and ‘speed on to Spica’ in the southwest.  Venus now moves away from Jupiter as they both gradually become lost in the Sun’s glare

The Summer Triangle is high in the east. This consists of the brightest stars in Cygnus, Lyra, and Aquila. Scorpius, the Scorpion, is in the south, with the ‘teapot’ of Sagittarius to his left. Leo, the Lion, sets in the west. From the Big Dipper’s handle, ‘arc to Arcturus’ and ‘speed on to Spica’ in the southwest. Venus now moves away from Jupiter as they both gradually become lost in the Sun’s glare

This is the last month to observe the two brightest planets in the western evening sky. On June 30, Venus overtook Jupiter. This month, watch Venus shift to the left of Jupiter each evening at dusk. Meanwhile, both planets appear lower and lower to the horizon each night, until they are both lost in the Sun’s glare by the end of the month. At dusk, look over the point of sunset for the brightest objects there; Venus and Jupiter outshine everything but the Sun and the Moon.

Saturn is now in the southern sky at dusk. Although it is not as brilliant as Venus or Jupiter, it outshines the stars around it, so it’s also easy to see.

Mars remains lost in the glare of the Sun.

The Big Dipper is above and left of the North Star, with its handle pointing up. From that handle, you can ‘arc to Arcturus’ and then ‘speed on to Spica’; those stars are in the southwest at dusk. Leo, the Lion, sets in the west at dusk.

Antares, brightest star of Scorpius, the Scorpion, is in the southeast, with the ‘teapot’ of Sagittarius rising behind it. Saturn is right above the scorpion’s head. The Summer Triangle has fully risen in the northeast. The stars of summer are here.

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Moon Phases in July 2015:

Full July 1, 9:20 pm; July 31, 5:43 am
Last Quarter July 8, 3:24 pm
New July 15, 8:24 pm
1st Quarter July 23, 11:04 pm

At 2:41 pm on Monday, July 6, Earth is as far from the Sun as it will get this year, a moment known as aphelion. Remember, though, that the difference between aphelion and perihelion (in January) is small (only about 3%). Earth’s 23.5 degree tilt on its axis is a much more important effect. That’s why we have all this miserable heat and humidity now, rather than in January.

Just before 6:50 am CDT on Tuesday, July 14, the New Horizons spacecraft makes its closest approach to Pluto. As this is our first opportunity ever to gather real data from Pluto and its moons, astronomers are quite excited. The craft is already close enough to take some pictures, which you can see here. The Museum will have special activities for this occasion; email me if you want more information.

The Full Moon of July 31 is the second one of the month. That’s one of the definitions of a Blue Moon.

Planetarium Schedule:

Brazos Bend State Park, where our George Observatory is sited, has been closed since May 27 because the rains of Memorial Day and of Tropical Storm Bill caused the Brazos to overflow. The park plans to reopen on a limited basis July 8, making July 11 the first Saturday available for public observing.

On most clear Saturday nights at the George Observatory, you can hear me do live star tours on the observation deck with a green laser pointer. If you’re there, listen for my announcement. I generally do one such tour on short June evenings.

Saturday’s the Summer Solstice: Five signs we’ve reached (another) Houston summer

Saturday’s the official beginning of summer! The day with the most sunlight (in the northern hemisphere), we’re now in the time of short shorts, trips to the beach, ice cream and vacations (and our Mixers & Elixirs Summer Solstice Party).

But summer in Houston is unique. We certainly know how to have a good time, but the weather doesn’t always make that easy. Here are five signs that we’ve reached summer in Houston:

YOU FEEL LIKE YOU’RE SWIMMING (WITHOUT THE REFRESHING PART)

The humidity in Houston is nothing to scoff at. Seriously. Stepping outside now feels like stepping into a hot mouth — or like you’re swimming, except you’re overheating.


AIR CONDITIONING IS MORE IMPORTANT THAN LITERALLY ANYTHING ELSE

Seriously, try and stay cool folks. Heat stroke is a real problem for Houstonians, especially for those on the younger or older ends of the age spectrum from June until August. Here are some helpful tips to keep cool.

YOUR ELECTRIC BILL HAS DOUBLED IN THE LAST MONTH

Again, AIR CONDITIONING = LIFE. However, this means your electric bill will almost certainly be the highest it’s been all year, especially if you’re using window units. Here are a few ways to be more efficient and lessen the impact

FORGETTING YOUR SUNGLASSES IS THE WORST THING THAT CAN HAPPEN

We’re no strangers to sunlight, but it just. gets. so. intense. Keep an extra pair in your car (you’ll be glad that first time you forget). Besides being able to see on the road, you’ll want them on whenever you’re outside to help fight against skin cancer, cataracts and macular degeneration

SLEEVES AND PANTS ARE NOW THE ENEMY

It’s just too hot to wear any more clothing than you need to remain decent in public. Besides, sweating is your natural way to keep cool. Don’t let fabric get in between you and comfort.

Now for some sweet relief: you can always come visit us and enjoy our cool exhibits away from the summer sun! So what are you waiting for?! 

And of course, you can beat the heat with Mixers & Elixirs this Saturday, June 21 at our Summer Solstice Party. Because when the Houston heat and HMNS coolness come together, things are bound to get steamy — the good kind.

A Trick or a Treat?

In less than a week, people all over the country, including right here at our museum, will be celebrating Halloween. Perhaps your workplaces and schools are already festooned with ghosts, skeletons, graveyards, and the like.  If you stop and think about it, you may wonder just how it is that we came to celebrate by trying to disguise ourselves or by trying to frighten people.  Is this a trick or a treat?

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Creative Commons License photo credit: joiseyshowaa

The short answer as to why we celebrate this time of year with images of death is that we are in the middle of autumn, the season when nature itself is dying.  To fully understand why we celebrate Halloween when we do, we must fully understand the seasons.

Earth orbits the Sun with its axis pointed at the North Star, Polaris. As a result, its axis is tilted by about 23.5 degrees with respect to its orbital plane.  This tilt, combined with Earth’s revolution around the Sun, causes the seasons.  If the North Pole leans towards the Sun, the Sun is higher in our sky and we get more direct sunlight.  Also, daytime is longer than nighttime.  As the North Pole begins to tilt away fron the Sun, the Sun appears lower and lower across the sky, and daytime gets shorter and shorter.  Eventually, the slanted-in solar rays and short days bring about winter.  Very cold air masses form in the darkened Arctic and begin to move south, some of which can even reach Houston.

Keep in mind that the Earth’s axis does not tilt back and forth; it points at Polaris the whole time.  In June, the North Pole is leaning towards the Sun, but by December, the Earth’s motion has carried it to the other side of the Sun.  The North Pole, still tilting the same way, now leans away from the Sun.

A common misconception is that the Earth is closer to the Sun in summer and more distant in winter, and that is what causes our seasons.  In fact, Earth’s perihelion (closest approach to the Sun) occurs just after the new year (January 1-4), while aphelion (greatest distance from the Sun) occurs around the 4th of July.  Earth’s orbit is an ellipse, but the Earth-Sun distance does not change by enough to affect our seasons.

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Creative Commons License photo credit: shioshvili

In the cycle of seasons, there are four points of note.  At the March equinox, neither pole is tilted toward the Sun and the Sun is directly overhead at the equator.  The is the vernal (spring) equinox for us and the autumnal (fall) equinox for folks south of the equator.  At the June solstice, the North Pole is tilted as much as possible towards the Sun, and the Sun is overhead at 23.5 degrees North (the Tropic of Cancer).  This is the summer solstice for us and the winter solstice in the Southern Hemisphere.  At the September equinox, once again neither pole tilts toward the Sun, and the Sun is again overhead at the equator.  This is our fall equinox and their spring equinox.  At the December solstice, the North Pole is tilted as much as possible away from the Sun, and the Sun is overhead at 23.5 degrees South (the Tropic of Capricorn).  This is the winter solstice for us and the summer solstice below the equator. 

We generally think of these points as the beginning of spring, summer, fall, and winter, but it doesn’t have to be that way.  After all, nothing magically happens with our weather on these dates.  We could just as well consider these points the midpoints of each season.  In that case, the seasons would begin and end at points roughly halfway between the equinoxes and solstices, in early February, May, August, and November.  If the equinoxes and solstices are ‘quarter days,’ the points halfway between them become the ‘cross-quarter days.’

The ancient Celts of Europe appear to have divided their year in precisely that way.  Gauls living in what is now France used a calendar of twelve lunar months with a 13th month added every 2.5 years (similar to the Hebrew calendar today).  Their two most significant months were Gamonios (lunar month corresponding to April/May ), which began the summer half of the year, and Samonios (lunar month corresponding to October/November) which began the winter half of the year.  Julius Caesar noted that daytime followed nighttime in Celtic days.  By extension, the dark (winter) half of the Celtic year preceded the light (summer) half, making Samonios the start of their new year.

The Celts in the British Isles (Irish and Scots) also had festivals aligned with the cross-quarter days.  In early February was Imbolc (or St. Brigid’s day).  Weather predicting traditions of this day are preserved in our current Groundhog Day.  Traditional May Day celebrations are similar to those of the Celtic BeltaneLughnasadh, in early August, marked the start of the harvest. 

'' The Sentiment of Light''
Creative Commons License photo credit: jdl_deleon

The most important, though, was Samhain (pronounced ’sah win’, not ‘Sam Hane’, due to rules of Gaelic spelling), in early November.  This three-day festival marked the beginning of the winter half of the year and the start of the whole year, like Gaulish Samonios.  It was the close of the harvest opened at Lughnasagh, and the time for culling excess livestock.  At this time, the veil between the living and the world of the dead was considered thinner than usual, and people looked forward to meeting and communing with ancestors and relatives who had died.  A ‘dumb supper‘ was set aside for departed relatives.  To scare away unwanted spirits, people dressed in frightening garb.  Note that these spirits were considered unpredictable and possibly mischievous because they were not the familiar ancestors–not because they were particularly evil.  Divination was also practiced at this time, as people sought to predict whom they would marry or how many children they would have. 

Doing the math, you’ve probably figured out that Halloween is not quite halfway from the equinox (September 22) to the solstice (December 21).  But remember, the Celts used a lunar calendar.  They celebrated their festivals on a certain phase of the Moon, possibly full moon, occurring nearest the cross-quarter day.  Upon the adoption of the Julian calendar, which was not strictly lunar, the festivals were moved to the beginning of February, May, August, and November, although this meant they were no longer exactly on the cross-quarter days. 

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Creative Commons License photo credit:
The Wandering Angel

In the eighth century AD, Pope Gregory III moved the church’s commemoration of the souls in heaven (All Saints’ Day) from May 13 to November 1.  Another name for All Saints’ Day is All Hallows Day.  (’Hallow’ is an older term for ’sanctify’ or ‘make holy.’  Think of ‘…hallowed be thy name’ from the Lord’s Prayer).  The next day became All Souls’ Day.  The day before All Hallows Day or All Saints’ Day is All Hallows Eve, or Halloween.  The traditions of Samhain, with its similar focus on honoring the dearly departed, were a natural fit for All Hallows Day and All Hallows Eve.

Halloween, then, is ultimately just one expression of the human need to come to terms with death as a natural occurence and to honor those who have gone before.  In the season of the fall of the leaf, with the Sun taking a slightly lower path across the sky each day, the natural world is going through its own ‘death,’ providing a perfect context for our own activities.  We can therefore think of Halloween itself as a treat, not a trick.

I wish everyone a Happy Halloween, with many more treats than tricks.