A solstice is when the Earth's axis is tilted in such a way that it is either the most inclined toward or away from the Sun. You may have noticed that the days have been longer and longer in recent weeks. You can be outside at 9pm and still see the Sun. That's because each day, the Earth's axis has tilted a little more toward the Sun. Unfortunately, today also marks the beginning of each summer day having a little less sunshine. Of course, I'm talking about those of us who live north of the equator. Because those living south of the equator have a different perspective by virtue of their geographic location.
For people living south of the equator, today's solstice means their part of the Earth is actually the furthest away from the Sun it will be all year. So while we, north of the equator, will be enjoying increasingly limited summer sunshine with each passing day, people in areas like Australia will be noticing a bit more sunshine and warmth on their end. Fascinating, isn't it?
But why does this happen?
It has to do with something called inertial space. All physical objects, like the Earth, are embedded in a background. Inertia itself is the opposition to any change of velocity in a physical object. Inertial space is key in understanding the solstice, because the orientation of the Earth via its tilted axis, either closer to or farther away from the Sun, is with respect to the surrounding inertial space.
The Earth's axis is also the reason for our seasons; the axis itself is at a 23.44-degree angle today, meaining it's not perpendicular with its orbital plane. The axis's maintenance of its orientation in respect to inertial space is also a factor in our seasons. So today, the Sun has reached its subpolar point in much of the northern hemisphere. The subpolar point is where the Sun is perceived to be directly overhead. In the northern hemisphere, that imaginary line is called the Tropic of Cancer. The reason why this imaginary line was called the Tropic of Cancer is because in early astronomy, the Sun was (from our perspective on Earth) in the direction of the Cancer Constellation. But because of axial progression, a gravity-induced slow but continuous change of a planet's rotational axis, during our current solstice, if you were to look to the skies today, you'd see that the Sun actually appears to be more toward the direction of the Taurus constellation.
German-born, Jewish physicist, Karl Schwarzschild (1873-1916), was the first to identify inertial space in 1899. While observing a double-star system, Schwarzschild noted that the angular momentum of all celestial bodies is an angular momentum with respect to inertial space. Though Schwarzschild, the father of prominent astrophysicist Martin Schwarzschild (1912-1997; Martin is known for major contributions to Galaxy Dynamics), is best known for being the first to solve Einstein's field equations for a singular spherical rotating mass in 1915 that helped to support Einstein's Theory of Relativity. Remarkably, Schwarzschild's contributions were made while he was fighting for Belgium during World War I. He volunteered to fight for his country and was stationed in Russia when he wrote his seminal papers regarding Einstein's Relativity. Unfortunately, Karl Schwarzschild contracted a disease during his military service in WWI that would lead to his eventual death two years later.
So today, while you enjoy the longest day of the year, try and remember that it's less about seasonal shift and more about astronomical events beyond our limited perception. We humans tend to take for granted exactly HOW and WHY things are the way they are on our planet. Part of the reason is that we are human-centric, believing that we are somehow the center of an expanding universe, when the fact is, only a very small percentage of the global population are astrophysicists (though it is hard to find an exact number). That means that the rest of us are simply ignorant to the BIGGER picture. But ignorance is the choice of the apathetic--never forget that. You may not be able to do the mathematics surrounding the science of astronomy or astrophysics (I certainly can't!), but luckily, you don't have to to learn more about our ever-increasing universe. We live in a technologically-capable world...so get out there and start surfing! Here are a few places to begin your life-long journey:
I guarantee you'll see the WORLD in a whole different light! For instance, did you know that a midnight rainbow was recorded on June 12th in Finland, a phenomenon only possible during the summer solstice??? Open your mind and your heart will follow. The basic principle of Einstein's Relativity is that things are much more simple, and therefore, much more connected, than we humans tend to recognize. Learning more about astrophyisics is perhaps MORE IMPORTANT to your daily life than watching the BP disaster continue or hearing about what politician is behaving badly or how the dollar sinks while gold values continue to rise. Don't just think GLOBALLY, think COSMICALLY.
Until next time, dearest readers....