「小寒」が寒冷な理由

　二十四節気では１月５日～１９日までの期間が「小寒」です。私たちを載せた地球は一周約９億４０００万kmのやや楕円の公転軌道上を、北極星側から見て反時計回りに毎秒約２９kmのスピードで１年間かけて公転してます。同時に、北極星側から見て反時計回りに２４時間かけて自転してます。

　ところで、今の季節に地球は一体どの辺を公転中でしょうか。また、今の季節は、何故寒いのでしょうか。

　と言っても、宇宙空間には地上のような目印なく、その代わり、太陽系を取り巻く「黄道十二星座」が目印になります。このため、これらの星座により地球の現在の位置を知ることができます。ですから答えは「午前０時に真南に輝く星座」を観察して、現在の地球の公転上の位置を知ります。

　ところで、今の季節では、夕方から明け方まで日本列島を覆うかの如く、巨大な「冬のダイアモンド」が一晩中輝いてます。私は、この「冬のダイアモンド」を初めて自分の目で把握したとき、あまりにも広大なので本当に感銘しました。

　「冬のダイアモンド」は最も明るい一等星シリウスや、オリオン座のリゲル、「牡牛座」のアルデバランなどすべて一等星で成してます。そして、実は、このダイアモンドを成す左上の一角に「ふたご座」があり、現在の地球はこの「ふたご座」の方向に来ています。中心は一等星のポリックスとカストロです。「午前０時に真南をご覧いただく」と現在の地球の公転上の位置は「ふたご座」の方角であることが分かります。

　一方、地球の自転軸は公転面に対し２３．５°ほど傾いたままで公転してます。このため、地上で見ると公転位置によって太陽高度が変化し、結果的に寒暖の差が生じ、現在、北極点が太陽から離れているので「北半球では太陽高度が低くなり」寒冷になります。

Dear my overseas friends who are interested in Nature and great music.

　The simultaneous interpretation for your understanding will be done after my breakfast Japan time.

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　According to the twenty-four solar terms in Japan, the period from January 5th to January 19th is "Shokan" that means little cold. The Earth which is carrying us, revolves around the sun in a slightly elliptical orbit of about 940 million km, moving counterclockwise from the North Star side at a speed of about 29 km per second over one year. At the same time, the earth rotates counterclockwise from the North Star side over 24 hours.

　By the way, where exactly is the Earth moving at this season of year? Also, why is it cold at this time of year?

　However, there are no landmarks in space like on the ground, and instead, the "12 Zodiacal Constellations" surrounding the solar system are used as landmarks. For this reason, we can understand the current position of the Earth by these constellations. The answer is to observe the "constellations shining due south at midnight" to find out the current position of the Earth on its orbit.

　By the way, at this time of year, a huge "Winter Diamond" shines all night long, as if it is covering the Japanese archipelago from dusk to dawn. When I first saw this "Winter Diamond" by my own eyes, I was really impressed by its vastness in the sky.

　The "Winter Diamond" is made up of all first magnitude stars, including the brightest first magnitude star Sirius, Rigel in Orion, and Aldebaran in Taurus. In fact, the constellation Gemini is in the upper left corner of this diamond, and the Earth is currently in the direction of Gemini. The center is the first magnitude stars Polyx and Castro in Gemini. If you look due south at midnight, you will find out that the Earth's current orbital position is in the direction of Gemini.

　On the other hand, the Earth's axis of rotation remains tilted at about 23.5 degrees relative to the orbital plane as it revolves. For this reason, when viewed from the ground, the solar altitude changes depending on the orbital position and seasons, resulting in temperature differences. Currently, the North Pole is far from the sun, so that the sun's altitude is lower in the Northern Hemisphere, it makes colder in Japan.

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