is a year, anyway?" Ignoring all cultural history, a year is basically the period of

忽略所有的文化歷史，一年基本上是一個時期的。

time that it takes for one physical body to orbit another. So an earth month could equally

一個物理體繞著另一個物理體運行所需的時間。所以一個地球月同樣可以

be called a "moon year."

被稱為"月年&quot。

But to under-simplify things, even if we stay on earth, there are several different ways

但是，簡單點說，即使我們留在地球上，也有幾種不同的方式。

to define a year — either the time it takes for the tilt

來定義一年--要麼是傾斜所需的時間。

of the earth's axis to come back to the same angle relative to the sun (called a tropical

地球的軸線回到同一角度相對於太陽（稱為熱帶）。

year) — or the amount of time before we come back

年）--或我們回來之前的時間。

and see the same stars rising behind the sun (called a sidereal year - pronounced like

並看到同樣的星星在太陽後面升起（稱為恆星年--發音就像...

ethereal) — or, since the earth follows an elliptical

虛無縹緲）--或者說，由於地球遵循的是一個橢圓型

orbit which precesses, we could measure the amount of time between closest approaches

我們可以測量最接近軌道的時間。

to the sun (this is called the anomalistic year).

到太陽（這叫異年）。

Of course, all three "years" have slightly different lengths. But our day-to-day civil

當然，這三個"年"的長度都略有不同。但我們日常的民

calendar does its best to follow the tropical year, since its duration is defined by the

由於熱帶年的持續時間是由熱帶雨林確定的，是以曆法儘量遵循熱帶年。

tilt of the earth's axis which also determines the passage of the seasons.

地球軸的傾斜度，也決定了四季的流逝。

There are non-earth years, too: Mercury's year is roughly 88 earth days, Neptune's is

也有非地球年的。水星的一年大約是88個地球日 海王星的一年大約是88個地球日。

165 earth years, and the "Galactic" year – which is how long the whole solar system takes to

165個地球年，以及"銀河年"年--也就是整個太陽系需要多長時間來

orbit once around the Milky Way – is around a quarter of a billion earth years! But not

繞銀河系運行一次--大約是25億地球年!但不是

all galactic years are long: check out this timelapse of stars orbiting the supermassive

所有的星系年都是漫長的：看看這段恆星繞超大品質星體運行的時間推移。

black hole at the center of the Milky Way! Even though you can't see the black hole,

銀河系中心的黑洞!儘管你看不到黑洞。

it's pretty obvious that it's there, what with all those stars zipping around in orbits

它很明顯，它在那裡， 什麼與所有這些恆星在軌道上飛馳周圍

taking only ten earth years! Astrophysicists have even used these orbits to figure out

只需要10個地球年！天體物理學家甚至利用這些軌道來計算出

that the black hole is as massive as 4 million suns.

黑洞的體積有400萬個太陽那麼大。

But enough about interstellar timekeeping… if you want to learn more about leap years

但關於星際計時的問題已經夠多了... 如果你想了解更多關於閏年的資訊... ...

here on Earth, check out Grey's new video over on his awesome channel, "cgpgrey"

在地球上，查看Grey'的新視頻在他的真棒頻道，"cgpgrey&quot。

And a big thanks to the UCLA Galactic Center for doing sweet supermassive black hole research

還要感謝加州大學洛杉磯分校銀河中心做的甜美的超大品質黑洞研究。

with the Keck telescope in Hawai'i, and for sharing their images with the public.

與凱克望遠鏡在夏威夷'i，並與公眾分享他們的影像。