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In the chilly (32 degrees) dark of 5 am this morning, as I gave my dogs their morning biscuits, I admired the form of the ‘Big Dipper’ almost directly overhead. I stood, bundled up, in the center of my starlit back garden – just admiring. Five am at the height of summer, I can be getting my coffee and heading out to begin playing in the garden, but in mid-December, as we near the richly-storied winter solstice – the longest night of the year in the Northern Hemisphere – crisp early mornings make for a great star-gazing; the entire garden is a virtual planetarium. Photo: The Moon and Jupiter in close proximity in the winter night sky. In the Northern Hemisphere, several well-known constellations are associated with winter. While many people of think of the ‘Big Dipper’ as a constellation, it is in fact more accurately an asterism – or part of a constellation or larger group of stars. The ‘Big Dipper’ is a commonly recognizable asterism of the larger constellation known as Ursa Major.
As gardeners, perhaps, we are even more aware than many of the shifts in light and its relative availability throughout the seasons and the year. Cultures across the globe have long celebrated the winter solstice and held it dear as the day on which the dark has reached its peak. As of the winter solstice, with every subsequent day, we are headed back toward the life-renewing light – the full intensity of the Sun’s energy.
Many gardeners time their planting and harvest – both the time at which they plant and harvest as well as what they are planting and harvesting – based on the phases of the moon. They do this in order to take full advantage of the powerful influence of the Moon’s on Earth as seen through tidal shifts, etc. In particular, the gardening/agricultural philosophy known as Biodynamics uses the phases of the moon as one of the critical markers for gardening tasks. According to Biodynamics.com, biodynamics, based on the teachings of Rudolph Steiner, the founder of Anthroposophy, is “a type of organic farming that incorporates an understanding of “dynamic” forces in nature not yet fully understood by science. By working creatively with these subtle energies, farmers are able to significantly enhance the health of their farms and the quality and flavor of food. It is ….. A recognition that the whole earth is a single, self-regulating, multi-dimensional ecosystem. Biodynamic farmers seek to fashion their farms likewise as self-regulating, bio-diverse ecosystems in order to bring health to the land and to their local communities.”
In thinking about the solstice and winter night sky in relation to my garden, I wondered about what the solstice actually was. To find out, I turned to friend and colleague Dave Schlom. Dave is a full-time science educator, and longtime host of Northstate Public Radio’s weekly program on planetary (including Earth) science, The Blue Dot Report. This week on In a North State Garden, Dave talks about what a solstice is and how it impacts us.
Let’s start with planet Earth and how it is positioned in space. The equator is what we call the great imaginary line (line of latitude) around Earth’s circumference. The equator lies half-way between the North Pole and the South Pole. Earth’s rotational axis is tilted 23.5° relative to the Sun. The Tropic of Cancer and the Tropic of Capricorn are lines of latitude 23.5° north and south, respectively, of the equator (Figure 3). The Sun is always directly above a point between these latitudes. In our winter, the Sun is south of the equator and in our summer it is north. What we in the Northern Hemisphere call the winter solstice, is the day that the Sun is 23.5° south of the equator, or directly above the Tropic of Capricorn. During the summer solstice, the sun is directly above the Tropic of Cancer, or 23.5° north of the equator. “That is why what we call the winter and summer solstices are perhaps more accurately referred to as the southern and northern solstices respectively,” explains Dave. Photo: NASA’s diagram of Earth’s position relative to the Sun at the time of a Northern Hemisphere Winter Solstice.
“In Latin,” he goes on, the word “‘solstice” means ‘sun stop’ because as ancient Roman people were tracking the arc of the Sun each day, it was at each ‘solstice’ that the Sun seemed to stop in its tracks and begin to move back in the other direction – causing daylight hours to either get longer as after the winter solstice, or shorter, as after the summer solstice. The vernal and autumnal equinoxes occur at those moments twice a year when the Sun is directly over the equator, making for equal hours of daylight and dark. http://www.worldatlas.com/aatlas/imagee.htm
Why is it cold in winter and warm in summer in our part of the world? The seasons change due to Earth’s rotational axis being tilted 23.5° relative to the Sun. So, for half of the year (our winter), the Northern Hemisphere is pointed slightly away from the Sun. This angle makes sunlight hit the ground in the North State at a lower angle in winter than in summer. So energy coming from the Sun is spread out – and thereby made less intense – over a larger area on the ground.
Interestingly, notes Dave, while the winter solstice might mark an official beginning of winter, it is only rarely the coldest day of the year. Because the Northern Hemisphere is moving only slowly more tilted away from the Sun’s rays from the summer solstice to the winter solstice, the mass of the Earth receives warmth from the sun each day and only slowly does it begin to lose more each night than it gains each day. Therefore, it takes a while after the winter solstice for the Earth to cool down as far as it is going to in any given winter.
So while the winter solstice does not mark the end of cold, but is closer to the beginning of the cold stretch for our North State gardens, this cold can be beneficial – killing unwanted fungi, pathogens and others pests. (Protect and cover your citrus and other tender plants so that the cold does not kill them.) The winter solstice does however mark the shortest day of the year – and while the cold temperatures and short daylight hours might slow your garden and you down some – things are only getting brighter from here.
Happy Winter in your North State Garden!
For more information on the solstice and stars in the winter night sky, Gateway Science Museum in Chico will be hosting related Education Station activities on Saturday and Sunday, December 17th and 18th, and on the Winter Solstice, December 21st from 1 – 3 pm each day. Docents will model the concept of a solstice, show you projections of constellations in the winter night sky, and give you pin-hole constellations cards to make and take home. Additionally, on the 21st, stories behind the winter constellations will be read in the Newberry Gallery from 1 – 3 pm.
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In a North State Garden is a weekly Northstate Public Radio and web-based program celebrating the art, craft and science of home gardening in Northern California and made possible in part by the Gateway Science Museum – Exploring the Natural History of the North State and on the campus of CSU, Chico. In a North State Garden is conceived, written, photographed and hosted by Jennifer Jewell – all rights reserved jewellgarden.com. In a North State Garden airs on Northstate Public Radio Saturday mornings at 7:34 AM Pacific time and Sunday morning at 8:34 AM Pacific time. Podcasts of past shows are available here.