The Daily Bucket is a nature refuge. We amicably discuss animals, weather, climate, soil, plants, waters and note life’s patterns.
We invite you to note what you are seeing around you in your own part of the world, and to share your observations in the comments below.
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June 24, 2019
Pacific Northwest
A few days ago was summer solstice, the date when the earth’s North Pole is tipped farthest toward the sun as our planet makes its yearly journey. Plants and animals have always oriented their life activities around the turn of the seasons, day length and intensity of sunlight being critically important to life. Humans noticed that variation early on too, and have devised an array of tools to measure it, since there’s usefulness in identifying the pattern for predictive purposes, ie. when’s maximum day length so I know when to plant/harvest etc.
A gnomon (name from gnō-, Proto-Indo-European root meaning "to know.”) is a tool that’s been used for at least 4000 years, first examples uncovered in China, later Babylonia, then Greece by 660 BC. A gnomon casts a shadow; the shape and movement of the shadow tells us about the relative movements of the earth and sun. Gnomons are used most frequently these days in decorative sundials, but they are more than just a fun garden novelty with a pithy motto. They work.
And if you know how they work a gnomon can be used in a survival situation, not just time of day but also which way is north (see the simple tutorial at this link, all you need is a stick, paper and pen, and a sunny day: www.mysundial.ca/...). You can even determine where you are in the world using gnomon!
My scale figure (Mr O) and I went down to the beach a couple of days before solstice and I snapped this photo exactly at noon (astronomical noon aka 1 pm on our current Pacific Daylight Time).
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Here’s Mr O on December 20 at noon (Pacific Standard Time) at the same spot.
Holy Mackerel, look at how long his shadow is at Winter Solstice compared to Summer Solstice!
You can tell immediately which way is north: the direction his shadow points (that’s because it’s noon). See the Sundial Primer diagram and link above for an explanation of why.
With a straight edge and a way to measure angles, you could also determine what latitude we’re at, one of the two numbers you need to pinpoint your location on earth. Latitude is how far north or south you are, between 90° S (the South Pole) through 0° (the equator) to 90° N (the North Pole). Longitude, where you are located east-west, is a lot trickier, and was only measured reliably starting in the 18th c (en.m.wikipedia.org/...). We forget in this day and age when GPS is so ubiquitous how difficult it is to locate yourself, and how potentially dangerous, without access to satellites and the internet.
To determine your latitude, it’s easiest at the solstices or equinoxes but this method could be used at any time of year with some interpolation. Discussion from NASA here: teacherlink.ed.usu.edu/…. First, measure the angle of the shadow cast by the gnomon, as below:
23 + 23.5 = 47.5 46.5
90 — 46.5 = 43.5°N
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68 - 23.5 = 44.5
90-44.5=45.5°N
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At winter solstice, add 23.5° to the measured angle. In my case I get 47.5° 46.5, which gives me elevation. Then subtract elevation from 90° for latitude: 90 — 46.5 = 43.5°N.
At summer solstice, subtract 23.5 from your measured angle. I get 44.5°. Subtract that from 90 for latitude: 90-44.5=45.5°N
(Above operations edited. Many thanks to cminus for catching my error and explaining how to do it right!)
My actual latitude here is 48.5°N. Not bad, considering how approximately I implemented this method.
Why does this method work, beyond just plugging in numbers? Let’s step back and look at why we have these different shadows. Diagrams from wikimedia will help visualize the situation.
The lower the sun in the sky, the longer the shadows cast. If you compare my photos above you’ll note that not only are buildings and bushes casting shadows on the road in winter but that the entire corner of the beach is in the shade. Not the case in summer.
Sunlight isn’t just longer in summer it’s also more intense, the same amount of radiation concentrated over a small patch rather than spread out. That’s why you get sunburned faster in summer, and why plants grow faster. Wear a hat and use sunscreen when you’re gardening or working outside. An Australian science site has a more detailed explanation, with a bonus: gives you an opportunity to see this whole seasons thing from a Southern Hemisphere point of view, where they have Christmas barbecues (www.abc.net.au/...).
Understanding the difference in the angle of the sun can be used in passive solar architecture to give you free heat and light in winter and free cooling in summer. Windows facing south allow low winter sun to enter the building, eaves above the windows shade them from intense summer sun.
This year’s summer solstice is behind us now but we have equinoxes and future solstices to come. You can locate a gnomon in your neighborhood to do some backyard science too!
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Sunny today in the islands. The birds totally used every bit of food in the feeders over the past few days. Summer solstice can be counted on to be peak birdy baby season.
(I got back late last night from a trip and am just now editing this draft for “todayness”.)
What’s the nature news in your neighborhood?
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