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Hey, Phil Plait here.
大家好，我是菲爾·普萊特。
Welcome to episode 2 of Crash Course Astronomy: Naked Eye Observations.
歡迎來到天文學速成班課堂第二集：肉眼觀察。
Despite the salacious title, nudity is not required.
儘管這個標題有點色情，但這個視頻裡是沒有裸體（同『naked』）的。
In fact, given that a lot of astronomical observations are done at night, you may want to bundle up.
事實上，考慮到很多天文觀測都是在晚上進行的，你可能會想要穿得暖和一點。
"One giant leap for mankind."
「人類的一大步。」
As it relates to astronomy, "naked eye" means no binoculars, no telescope.
這個詞是與天文學有關的，「肉眼」意味著沒有雙筒望遠鏡，不使用望遠鏡。
Just you, your eyeballs, and a nice, dark site from which to view the heavens.
只有你，你的眼球，和一個美麗的、黑暗的可以看到天空的地方。
After all, that's how we did astronomy for thousands of years, and it's actually pretty amazing what you can figure out about the Universe just by looking at it.
畢竟，這就是我們用了幾千年的研究天文學的方法，而且實際上，你通過用雙眼觀察就能了解宇宙，這是非常驚人的。
Imagine you're somewhere far away from city lights, where you have an unobstructed view of the cloudless sky.
想像一下，你在一個遠離城市燈光的地方，在那裡你可以一覽無餘地看到萬裡無雲的天空。
The Sun sets, and for a few minutes you just watch as the sky darkens.
太陽落山，幾分鐘的時間裡，你就看著天空變暗。
Then, you notice a star appear in the east, just over a tree.
然後，你注意到一顆星星出現在東方，就在一棵樹的上方。
Then another, and another, and within an hour or so you are standing beneath an incredible display, the sky spangled with stars.
然後又是一個接著一個，不到一個小時左右，你的頭頂就是一番壯觀的景象，滿天都是閃爍著的星星。
What do you notice right away?
你馬上會注意到什麼？
First, there are a lot of stars.
首先，有很多星星。
People with normal vision can see a few thousand stars at any given time, and if you want a round number, there are very roughly six to ten thousand stars in total that are bright enough to detect by eye alone, depending on how good your sight is.
視力正常的人在任何時候都能看到幾千顆星星，大概的數字約是6到1萬顆，它們的亮度僅憑肉眼就能觀察到，這也取決於你的視力有多好。
The next thing you'll notice is that they're not all the same brightness.
你會注意到的下一件事就是它們的亮度不一樣。
A handful are very bright, a few more are a bit fainter but still pretty bright, and so on.
有一些非常亮，有一些稍微暗一些但仍然很亮，等等。
The faintest stars you can see are the most abundant, vastly outnumbering the bright ones.
你能看到的最暗的星星是數量最多的，遠遠超過明亮的星星。
This is due to a combination of two effects.
這是由於兩種效應的結合所致。
One is that stars aren't all the same intrinsic, physical brightness.
一是恆星的固有、物理亮度不盡相同。
Some are dim bulbs, while others are monsters, blasting out as much light in one second as the Sun does in a day.
它們有些像是昏暗的燈泡，而另一些則像怪物一般，一秒鐘發出的光就相當於太陽一天發出的光。
The second factor is that not all stars are the same distance from us.
第二個因素是，不是所有的星星離我們的距離都是一樣的。
The farther away a star is, the fainter it is.
離我們越遠，它就越暗。
Interestingly, of the two dozen or so brightest stars in the sky, half are bright because they're close to Earth, and half are much farther away but incredibly luminous, so they still appear bright to us.
有趣的是，在天空中二十多顆最亮的星星中，其中有一半看起來很亮是因為它們離地球很近，而另一半則遠得多，但卻非常明亮，所以它們在我們看來仍然很亮。
This is a running theme in astronomy, and science in general.
這是天文學和一般科學中經常出現的主題。
Some effects you see have more than one cause.
你看到的一些現象不止受一個原因所影響。
Things aren't always as simple as they seem.
事情並不總是像看上去那麼簡單。
The ancient Greek astronomer Hipparchus is generally credited for creating the first catalog of stars, ranking them by brightness.
古希臘天文學家希帕克斯創造了第一個恆星錄，並根據亮度對它們進行了排序。
He came up with a system called magnitudes, where the brightest stars were 1st magnitude, the next brightest were 2nd magnitude, down to 6th magnitude.
他提出了一個叫做光度量級的系統，其中最亮的恆星是1級，其次是2級，一直到最後是6級。
We still use a variation of this system today, thousands of years later.
幾千年後的今天，我們仍然在使用這個系統的變體。
The faintest stars ever seen (using Hubble Space Telescope) are about magnitude 31 — the faintest star you can see with your eye is about 10 billion times brighter!
最暗的恆星（使用哈勃太空望遠鏡觀測）大約是31級——你用眼睛能看到的最暗的恆星要比這亮大約100億倍！
The brightest star in the night sky — called Sirius, the Dog Star — is about 1000 times brighter than the faintest star you can see.
夜空中最亮的星星——天狼星——比你能看到的最暗的星星還要亮1000倍。
Let's take a closer look at some of those bright stars, like, say, Vega.
讓我們仔細看看那些明亮的星星，比如織女星。
Notice anything about it?
注意到什麼了嗎？
Yeah, it looks blue.
是的，它看起來是藍色的。
And Betelgeuse looks red.
獵戶座α星看起來是紅色的。
Arcturus is orange, Capella yellow.
大角星是橙色的，五車二（御夫座之一等星）是黃色的。
Those stars really are those colors.
那些星星真的就是那樣的顏色。
By eye, only the brightest stars seem have color, while the fainter ones all just look white.
肉眼看來，只有最亮的星星才有顏色，而那些暗一些的星星看起來都是白色的。
That's because the color receptors in your eye aren't very light-sensitive, and only the brightest stars can trigger them.
這是因為你眼睛裡的顏色感受器對光線不是很敏感，只有最亮的星星才能觸發它們。
Another thing you'll notice is that stars aren't scattered evenly across the sky.
你會注意到的另一件事是，星星並非均勻地散布在天空中的。
They form patterns, shapes.
它們會形成某種圖案、形狀。
This is mostly coincidence, but humans are pattern-recognizing animals, so it's totally understandable that ancient astronomers divided the skies up into constellations (literally sets or groups of stars), and named them after familiar objects.
這大多是巧合，但人類是能識別模式的動物，所以古代天文學家就把天空分成不同的星座（字面意思是「星星的集合或群」），並以與其相似的物體來命名，這是完全可以理解的。
Orion is probably the most famous constellation; it really does look like a person, arms raised up, and most civilizations saw it that way.
獵戶座可能是最著名的星座，它確實看起來像一個舉著手臂的人，大多數文明也都是這麼看的。
There's also tiny Delphinus; it's only five stars, but it's easy to see it as a dolphin jumping out of the water.
還有小海豚座，它只有五顆星，但很容易看出它像一隻海豚跳出水面的樣子。
And Scorpius, which isn't hard to imagine as a venomous arthropod.
還有蠍子座，不難把它想像成一種有毒的節肢動物。
Others, well, not so much.
其他的，就沒這麼像了。
Pisces is a fish?
雙魚座看著像魚嗎？
Yeah, OK.
行，好吧。
Cancer is a crab?
巨蟹座看著像螃蟹嗎？
If you say so.
如果你非要這麼說的話，也行。
Although they were rather arbitrarily defined in ancient times, today we recognize 88 official constellations, and their boundaries are carefully delineated on the sky.
雖然這在古代是相當武斷的命名，但今天我們承認了88個官方星座，它們的在天空中的邊界被描繪得很清晰。
When we say a star is in the constellation of Ophiuchus, it's because the location of the star puts it inside that constellation's boundaries.
當我們說一顆星在蛇夫座的時候，那是因為這顆星的位置在蛇夫座的邊界內。
Think of them like states in the US: the state lines are decided upon by mutual agreement, and a city can be in one state or the other.
可以把它們想像成美國的州：州界是由雙方協議決定的，一個城市可以位於其中一個州，也可以位於另一個州。
Mind you, not every group of stars makes a constellation.
請注意，不是每一組恆星都構成一整個星座。
The Big Dipper, for example, is only one part of the constellation of Ursa Major, the Big Bear.
例如，北鬥七星只是大熊星座的一部分。
The bowl of the dipper is the bear's haunches, and the handle is its tail.
北鬥七星的碗型部分是熊的腰，柄則是熊的尾巴。
But! Bears don't have tails!
但是！熊沒有尾巴！
So astronomers might be great at pattern recognition, but they're terrible at zoology.
所以天文學家可能很擅長識別模式，但在動物學方面卻很糟糕。
Most of the brightest stars have proper names, usually Arabic.
大多數最亮的星星都有自己的名字，通常是阿拉伯語。
During the Dark Ages, when Europe wasn't so scientifically minded, it was the Persian astronomer Abd al-Rahman al-Sufi who translated ancient Greek astronomy texts into Arabic, and those names have stuck with us ever since.
在黑暗時代，歐洲還沒有那麼系統科學的思想，是波斯天文學家 Abd al-Rahman al-Sufi 把古希臘天文學文獻翻譯成了阿拉伯語，這些名字至今仍留在我們腦海中。
However there are a lot more stars than there are proper names, so astronomers use other designations for them.
然而，恆星的數量遠遠多於它們的專有名稱，所以天文學家們又用了其他的名稱來稱呼它們。
The stars in any constellation are given Greek letters in order of their brightness, so we have Alpha Orionis, the brightest star in Orion, then Beta, and so on.
任何星座的星星都是用希臘字母排序的，所以我們有獵戶座α星（最亮的一顆），然後是β星，等等。
Of course, you run out of letters quickly, too, so most modern catalogs just use numbers; it's a lot harder to run out of those.
當然，這樣很快就會用完所有的字母，所以大多數現代的目錄編排就使用數字，如此就很難窮盡了。
Of course, just seeing all those faint stars can be tough, which brings us to this week's "Focus On."
當然，光是看那到些暗淡的星星就很困難，這就引出了我們本周的「聚焦知識點」。
Light pollution is a serious problem for astronomers.
光汙染是天文學家面臨的一個嚴重問題。
This is light from street lamps, shopping centers, or wherever, where the light gets blasted up into the sky instead of toward the ground.
即指的是那些來自街燈、購物中心或其他地方的光，它們都射向了天空而不是地面。
This lights the up the sky, making fainter objects much more difficult to see.
這便照亮了天空，使本就比較模糊暗淡的物體更難以看到了。
That's why observatories tend to be built in remote areas, as far from cities as possible.
這就是為什麼天文臺往往建在偏遠地區、離城市越遠越好的原因了。
Trying to observe faint galaxies under bright sky conditions is like trying to listen to someone 50 feet away whispering at you at a rock concert.
試圖在明亮的天空下觀察暗淡的星系，就好比在搖滾音樂會上試圖聽一個50英尺外的人對你的低語。
This affects the sky you see as well.
這也會影響你看到的天空。
From within a big city, it's impossible to see the Milky Way, the faint streak of across the sky that's actually the combined light of billions of stars.
在一個大城市裡，你不可能看到銀河——划過天空的那道微光實際上是數十億顆恆星發出的光的總和。
It gets washed out with even mild light pollution.
即使是輕微的光汙染也會把它的色澤衝淡。
Your view of Orion probably looks like this.
獵戶座的圖像大概是這樣的。
When from a dark site it looks like this.
而在黑暗的地方看，它就是這樣的。
It's not just people who are affected by this, either.
而且，也不僅僅是人們受到了影響。
Light pollution affects the way nocturnal animals hunt, how insects breed, and more, by disrupting their normal daily cycles.
光汙染會影響夜行動物的捕獵方式、昆蟲的繁殖方式，等等，因為光汙染會擾亂它們正常的日常循環。
Cutting back light pollution is mostly just a matter of using the right kind of light fixtures outside, directing the light down to the ground.
減少光汙染主要就是在室外使用合適的燈具，引導光線射到地面上。
A lot of towns have worked to use better lighting, and have met with success.
許多城鎮都努力使用更好的照明系統，並取得了成功。
This is due in large part to groups like the International Dark-Sky Association, GLOBE at Night, The World at Night, and many more, who advocate using more intelligent lighting, and to help preserve our night sky.
這在很大程度上要歸功於國際暗天協會、夜空觀星(GLOBE at Night)、夜間世界(the World at Night)等組織，他們提倡使用更智能的照明，幫助保護我們的夜空。
The sky belongs to everyone, and we should do what we can to make sure it's the best possible sky we can see.
天空屬於每一個人，我們應該盡我們所能來確保這是我們所能看到的最好的天空。
Even if you don't have dark skies, there's another thing you can notice when you look up.
即使沒有黑暗的天空，當你抬頭看的時候，你也會注意到另一件事。
If you look carefully, you might see that a couple of the brightest stars look different than the others.
如果你仔細觀察，你可能會發現一些明亮的星星看起來與其他的星星不同。
They don't twinkle!
它們不會閃爍！
That's because they aren't stars, they're planets.
那是因為它們不是恆星，而是行星。
Twinkling happens because the air over our heads is turbulent, and as it blows past, it distorts the incoming light from stars, making them appear to slightly shift position and brightness several times per second.
星星之所以會閃爍，是因為我們頭頂上的空氣是湍流的，當它吹過的時候，會扭曲來自恆星的入射光，使它們的位置和亮度每秒發生幾次輕微的改變。
But planets are much closer to us, and appear bigger, so the distortion doesn't affect them as much.
但是行星離我們更近，而且看起來更大，所以那種扭曲對它們的影響沒有那麼大。
There are five naked eye planets (not counting Earth): Mercury, Venus, Mars, Jupiter, and Saturn.
有五顆肉眼可見的行星（不包括地球）：水星、金星、火星、木星和土星。
Uranus is right on the edge of visibility, and people with keen eyesight might be able to spot it.
天王星在我們視野可見的邊緣，目光敏銳的人可能會看到它。
Venus is actually the third brightest natural object in the sky, after the Sun and Moon.
金星實際上是天空中第三亮的自然天體，僅次於太陽和月亮。
Jupiter and Mars are frequently brighter than the brightest stars, too.
木星和火星也常常比最亮的恆星還要亮。
If you stay outside for an hour or two, you'll notice something else that's pretty obvious: the stars move, like the sky is a gigantic sphere wheeling around you over the course of the night.
如果你在外面呆上一兩個小時，你會注意到其他一些非常明顯的事情：星星在移動，就像天空是一個巨大的球體，一整夜都在你周圍轉。
In fact, that's how the ancients thought of it.
事實上，古人就是這麼想的。
If you could measure it, you'd find this celestial sphere spins once every day.
如果你能測量的話，你會發現這個天球每天旋轉一次。
Stars toward the east are rising over the horizon, and stars in the west are setting, making a big circle over the course of the night (and presumably, day).
東方的星星在地平線上升起，西方的星星則落下，在夜晚（也可以假定是白天）形成一個大圓圈。
This is really just a reflection of the Earth spinning, of course.
當然，這只是地球自轉的一種反映。
The Earth rotates once a day, and we're stuck to it, so it looks like the sky is spinning around us in the opposite direction.
地球每天自轉一次，而我們身處地球之中，所以看起來好像是天空在繞著我們朝相反的方向旋轉。
There's an interesting thing that happens because of this.
因為這個，有趣的事情就發生了。
Look at a spinning globe.
觀察一下一個會旋轉的地球儀。
It rotates on an axis that goes through the poles, and halfway between them is the Equator.
它繞著穿過兩極的軸旋轉，而在兩極中間的就是赤道。
If you stand on the Equator, you make a big circle around the center of the Earth over a day.
如果你站在赤道上，你用一天的時間就繞著地球中心轉了一個大圓。
But if you move north or south, toward one pole or the other, that circle gets smaller.
但是如果你向北或向南移動，朝向一個極點或另一個極點，這個圓就會變小。
When you stand on the pole, you don't make a circle at all; you just spin around in the same spot.
當你站在杆子上時，你根本不需要繞一圈，你就只是在原地旋轉。
It's the same thing with the sky.
天空也是一樣。
As the sky spins over us, just like with the Earth, it has two poles and an Equator.
當天空在我們上空旋轉時，就像地球一樣，它也有兩極和赤道。
A star on the celestial Equator makes a big circle around the sky, and stars to the north or south make smaller ones.
天球赤道上的星星圍繞天空會形成一個大圓，而南北方向的星星則形成較小的圓。
A star right on the celestial pole wouldn't appear to move at all, and would just hang there, like it was nailed to that spot, all night long.
一顆在天極上的星星看起來不會移動，只是掛在那裡，就像被釘在那點上一樣，一整夜都是如此。
And this is just what we see!
這就是我們所看到的景象！
Photographic time exposures show it best.
曝光照片最能說明這一點。
The motions of the stars show up as streaks.
星星的運動軌跡呈現條紋狀。
The longer the exposure, the longer the streaks as the stars rise and set, making their circular arcs in the sky.
曝光時間越長，星星在天空中形成圓弧的起落軌跡也就越長。
You can see stars near the celestial equator making their big circles.
你可以看到恆星在天球赤道附近形成大的圓圈。
And, by coincidence, there's also a middling-bright star that sits very close to the north celestial pole.
巧合的是，還有一顆中等亮度的恆星非常靠近北天極。
That's called Polaris, the north or pole star.
那就是北極星。
Because of that, it doesn't appear to rise or set, and is always to the north, motionless.
正因為如此，它看起來既不會上升也不會下降，總是朝向北靜止不動。
It really is coincidence; there's no southern pole star, unless you count Sigma Octans, a dim bulb barley visible by eye that's not all that close to the south pole of the sky anyway.
這真是巧合；沒有南極星，除非你算上σ南極星座，它是一種肉眼可見的暗淡星星，但離南極也不是那麼近。
But even Polaris isn't exactly on the pole — it's offset a teeny bit.
但即使是北極星也不是完全在極點上——它有一點點偏移。
So it does make a circle in the sky, but one so small you'd never notice.
所以它確實在天空中形成了一個圓圈，但它小得你根本注意不到。
By eye, night after night, Polaris is the constant in the sky, always there, never moving.
夜復一夜用肉眼觀察，都會發現北極星在天空中是固定不動的，它總是在那裡，從不移動。
Remember, the sky's motion is a reflection of the Earth's motion.
記住，天空的運動就是地球運動的反映。
If you were standing on the north pole of the Earth, you'd see Polaris at the sky's zenith — that is, straight overhead — fixed and unmoving.
如果你站在地球的北極，你會看到北極星在天空的最高點——也就是頭頂上——固定不動。
Stars on the celestial equator would appear to circle the horizon once per day.
在天球赤道上的星星每天會在地平線上繞過一圈。
But this also means that stars south of the celestial equator can't be seen from the Earth's north pole!
但這也意味著從地球的北極看不見天球赤道以南的恆星！
They're always below the horizon.
它們總是在地平線以下。
So this in turn means that which stars you see depends on where you are on Earth.
這就意味著你能看到哪些恆星取決於你在地球上所處的位置。
At the north pole, you only see stars north of the celestial equator.
在北極，你只能看到天球赤道以北的星星。
At the Earth's south pole, you only see stars south of the celestial equator.
在地球的南極，你只能看到天球赤道以南的恆星。
From Antarctica, Polaris is forever hidden from view.
從南極看，北極星則永遠隱藏在視野之外。
Standing on the Earth's equator, you'd see Polaris on the horizon to the north, and Sigma Octans on the horizon to the south, and over the course of the day the entire celestial sphere would spin around you; every star in the sky is eventually visible.
站在地球的赤道上，你會看到北極星在北邊的地平線上，σ南極星座在南邊的地平線上，一天之內整個天球都會圍繞著你旋轉；最終天空中的每一顆星星都是可以被看見的。
While Polaris may be constant, not everything is.
雖然北極星可能是固定不動的，但並不是所有的東西都是不移動的。
Sometimes you just have to wait a while to notice.
有時你只是需要等待一段時間才能注意到。
And to that point, you'll have to wait a while to find out what I mean by this, because we'll be covering that in next week's episode.
關於這一點，你要等一段時間才能知道我說的是什麼意思，因為我們下周的課會講到。
Today we talked about what you can see on a clear dark night with just your eyes: thousands of stars, some brighter than others, arranged into patterns called constellations.
今天，我們講到了在一個晴朗的黑夜裡，僅憑肉眼所能看到的景象：成千上萬的星星，其中有的比其他的更亮，它們排列組合成被稱為星座的圖案。
Stars have colors, even if we can't see them with our eyes alone, and they rise and set as the Earth spins.
星星是有顏色的，即使我們無法僅靠雙眼就看到它們，它們會隨著地球自轉而升起和落下。
You can see different stars depending on where you are on Earth, and if you're in the northern hemisphere, Polaris will always point you toward north.
根據你在地球上所處的位置，你可以看到不同的星星，如果你在北半球，北極星就總是會指向北方。
Crash Course is produced in association with PBS Digital Studios.
Crash Course 是與 PBS 數字工作室聯合製作的。
This episode was written by me, Phil Plait.
我是菲爾·普萊特，這一集是由我創作的。
The script was edited by Blake de Pastino, and our consultant is Dr. Michelle Thaller.
腳本由 Blake de Pastino 編輯，我們的顧問是 Michelle Thaller 博士。
It was co-directed by Nicholas Jenkins and Michael Aranda, and the graphics team is Thought Café.
本片由尼古拉斯·詹金斯(Nicholas Jenkins)和麥可·阿蘭達(Michael Aranda)聯合執導，視頻畫麵團隊是 Thought Cafe。