入秋第一天 背后有哪些科学原理？

It's time to say goodbye to summertime because today is officially the first day of fall, also called autumnal equinox.

该是告别夏日的时候了，因为今天是秋天的第一天，也被称为秋分。

During the vernal and autumnal equinoxes, the sun is directly over the equator, so day and night are considered to be the same length.

在春分和秋分期间，太阳直射赤道，因此白昼和黑夜有着相同的长度。

If you reside in the northern hemisphere, you know it is the start of fall, but folks down south of the equator, this equinox is actually the start of spring.

如果你居住在北半球，这时候是秋天的开始，但对于居住在赤道以南的人们来说，这个昼夜平分日实际上是春天的开始。

This is not to be confused with a solstice though.

不要把它和夏至或冬至相混淆。

Those are in the summer and the winter and represent the longest and shortest days of the year respectively.

夏至和冬至出现在夏天和冬天，分别代表一年中最长和最短的日子。

So when it comes to fall, you might be thinking about colder temperatures, pumpkin spice lattes, some football or fallen leaves.

说到秋天，你可能会想到越来越冷的温度，南瓜香辛拿铁，足球或落叶。

And speaking of leaves, let's take a minute to learn why they actually change color in the fall.

说到树叶，让我们花点时间来了解一下它们为什么会在秋天变色。

I want you think about leaves on a tree as essentially many solar panels.

你们可以把树上的叶子想象成很多太阳能电池板。

What they're able to do is fascinating.

树叶变化的过程趣味无穷。

They are taking the sunlight in and through a process known as photosynthesis.

树叶通过一种被称为光合作用的过程吸收阳光。

They're able to transfer the sun's energy and create a chemical known as chlorophyll.

树叶能够转移太阳的能量，产生一种被称为叶绿素的化学物质。

Now, chlorophyll is key because it gives the leaves its green colors during the long summer months.

叶绿素是关键，因为该物质使树叶在漫长的夏季保持绿色。

But beneath the surface, the leaves actually always have the reds, the oranges, the yellows in place while chlorophyll is there, it's there and it's green.

但在叶面之下，树叶实际上在有的地方呈红色、橙色和黄色，而叶绿素所在的位置呈现的是绿色。

While it's taken away in the shorter days and shorter months of the autumn, now you're releasing some of the true colors back to the surface.

秋季月份变得越来越短，白昼也变得越来越短，叶绿素也随之被带走了，现在树叶真正的颜色释放回了叶面上。

Of course, weather can play a role in this as well, especially in the vibrancy of it.

当然，天气也会在其中发挥作用，尤其是当秋风刮过的时候。

When you have plenty of rainfall in the growing season or in the spring season, you're able to get plenty of good colors in early September, October and November.

当在万物生长的春季迎来充足的降雨时，就能在9月初、10月和11月观赏到各种各样的颜色。

If you have extreme heat, extreme drought in place, maybe a freeze early snowstorm or even strong winds, certainly that can do damage.

如果遇到极端高温，极端干旱，或是提早来的冰雪风暴，甚至是强风，自然会对树叶造成破坏。

The leaves will not be there for you to see them in peak foliage.

你也就无法看到树叶的巅峰状态了。

So hopefully, you get a chance to get out there this year and enjoy the fall colors.

希望今年你有机会走出家门，观赏秋天的色彩。