緯度により太陽の高さが異なる

 国立天文台によると、今日６月１４日の群馬県の日の出は４時２５分で、夏至より今日の方が１分早いです。日の入りは１９時０３分で、こちらは夏至の方が２分遅いです。正午の太陽高度は約７６°ですが、梅雨の最中であり、確認できません。

　しかし、太陽高度については、地球の自転の傾きである２３．４°、及び、住んでる位置の緯度により計算できます。例えば、群馬県高崎市は北緯３６度１９分ですから、北極点９０°－北緯３６°１９′＋地球の傾き２３．４°＝約７６°です。

　昔、滞在してたカルカッタ市では今の季節に、正午の太陽は少し北に出たので不思議な体験でした。北回帰線より南の北緯２２度だからです。と言うことは、インドでは一年を通じて、太陽はほぼ真上から照っており、夏休みである５月の気温は連日４０度を超えてます。正午に外に出ても自分の影がありません。私も「影のない人間になったのか」と思いましたが、そうではありません。影は自分で踏んでるのです。

　一方、今の季節に北極点では、太陽は一日中、沈みません。地球が反時計回りに自転してるので、太陽は時計回りに東～南～西～北へと一周し、その高さは地平線から地軸の傾きの２３.４°で一日中、変わりません。北極圏でも今の季節に太陽は一日中沈まず、北欧などでは白夜が続いてます。反対に、南極では今の季節は昼がなく夜が連続してます。

　このようなことを考えると、私たちは温帯の日本に生まれて本当に良かったです。色彩豊かに花が咲き、果物が生り、四季を通じて会いたい人に会えます。

Dear my friends who are crazy about nature, humans and great music.

　The simultaneous interpretation into English for our mutual understanding will be done after my breakfast in Japan time.

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　According to the National Astronomical Observatory of Japan, today, June 14th, sunrise in Gumma Prefecture is at 4:25, which is one minute earlier than the summer solstice. Sunset is at 19:03 which is two minutes later than the summer solstice. The solar altitude at noon is about 76°, but since we are in the middle of the rainy season, we cannot confirm this.

　However, the solar altitude can be calculated using the Earth's tilt of 23.4° and the latitude of where we live. For example, Takasaki City, Gumma Prefecture, is at 36 degrees 19 minutes north, so the North Pole latitude 90° - 36 degrees 19' north + rotational tilt 23.4° = about 76°.

　When I used to stay at Calcutta in India, it was a strange experience that the sun passed a little north at noon during this season. This is because the latitude there is 22 degrees north　where is more southern than the Tropic of cancer. This means that in India, the sun shines almost directly above throughout the year, and the temperature in May, which is summer vacation, exceeded 40 degrees in Celsius every day. When I went outside at noon, I didn't see my shadow. I thought to myself, "Have I become a person without a shadow in heart?" but that's not the case. My stepped on my own shadow.

　Meanwhile, at this season, the sun doesn't set all day long at the North Pole. As the Earth rotates counterclockwise, the sun makes a full circle clockwise from east to south to west to north, and its height from the horizon remains constant throughout the day at 23.4°, due to the tilt of the Earth's axis. Even in the Arctic Circle, the sun doesn't set at this season of year, and in places in Northern Europe, there are continuous sunshine all day long. In contrast, in the Antarctic, there is no sunshine and only continuous nights at this season of year.

　When I think about these phenomenon, it's really great that we were born in temperate Japan. Colorful flowers bloom, fruit grows, and I can meet the person whom I want to meet throughout the four seasons.