Light seconds, light years, light centuries: How to measure extreme distances - Yuan-Sen Ting
Summary
TLDR这段视频脚本以光速为引子,探讨了宇宙的广阔和我们如何测量天体的距离。光年是描述光一年内行进距离的单位,大约为6万亿英里。通过三角视差法,我们可以测量相对较近的恒星的距离,但这种方法对于更远的星系则不适用。此时,我们使用标准烛光法,即通过已知亮度的天体(如造父变星和Ia型超新星)来估算距离。这些方法使我们能够观测到数十亿光年外的宇宙,而我们看到的光实际上是宇宙过去的图像。通过观测这些遥远的天体,天体物理学家可以解读宇宙的历史,了解我们的起源。
Takeaways
- 🌌 光是我们知道的最快的事物,它的速度如此之快,以至于我们通过光行进的时间来测量巨大的距离。
- 📏 一年内,光可以行进约6万亿英里,这个距离被称为一光年。
- 🌕 月球距离地球只有一光秒,而阿波罗宇航员需要四天时间才能到达。
- 🌟 最接近我们太阳的恒星是比邻星,距离我们4.24光年。
- 🌌 我们的银河系大约有10万光年宽。
- 🌌 离我们最近的仙女座星系大约有250万光年远。
- 🔍 通过三角视差法,我们可以测量相对较近的天体距离,通过观察地球绕太阳公转六个月期间恒星位置的相对变化。
- 🕯️ 标准烛光是我们知道其固有亮度的物体,例如造父变星,通过测量其亮度变化周期来计算其亮度。
- 💥 1a型超新星是另一种标准烛光,它们的亮度和衰减率之间的关系使我们能够测量数十亿光年远的距离。
- ⏳ 观察遥远天体实际上是在回望时间,因为光从那些天体到达我们这里需要时间。
- 🔭 天文学家利用光作为信息的载体,尝试解读宇宙的历史,理解我们的起源。
Q & A
光的速度有多快?
-光是我们所知道最快的事物,它在一年内可以传播约6,000,000,000,000英里,这个距离我们称为一光年。
什么是光年?
-光年是描述光在一年时间内可以传播的距离,它是一个用来衡量巨大距离的单位。
月球离地球有多远?
-月球离地球只有一光秒的距离,阿波罗宇航员用了四天时间才到达月球。
我们最近的恒星是哪一个?
-除了我们的太阳之外,最近的恒星是比邻星(Proxima Centauri),距离我们大约4.24光年。
我们的银河系有多大?
-我们的银河系大约有100,000光年宽。
我们最近的星系是什么?
-我们最近的星系是仙女座星系,距离我们大约2.5百万光年。
天文学家如何测量恒星和星系的距离?
-对于非常近的天体,天文学家使用三角视差法来测量距离。通过观察半年后地球绕太阳公转时恒星的视位置变化,可以计算出它们的距离。
什么是标准烛光?
-标准烛光是那些我们非常了解其固有亮度或光度的天体。例如,造父变星和Ia型超新星,它们因为特定的光度变化规律,可以用来估算距离。
为什么我们能看到数亿光年远的超新星?
-Ia型超新星的爆炸非常明亮,它们的光芒可以盖过它们所在的星系,因此即使我们无法分辨星系中的单个恒星,我们仍然可以看到这些超新星。
为什么观察遥远天体很重要?
-观察遥远天体就像是使用宇宙内建的时间机器。我们看到的光是过去的图像,通过观察这些遥远的对象,我们可以回溯到宇宙的早期状态,了解宇宙的历史。
太阳发出的光需要多久才能到达我们?
-太阳发出的光需要大约8分钟才能到达我们,这意味着我们现在看到的是8分钟前的太阳。
当我们观察北斗七星时,我们看到的是多久前的图像?
-当我们观察北斗七星时,我们看到的是大约80年前的图像,因为光从那里传播到我们这里需要这么长时间。
宇宙通过什么方式向我们发送信息?
-宇宙通过光的形式向我们发送信息,我们的任务是解码这些信息,以更好地理解宇宙。
Outlines
🚀 光速与宇宙尺度
本段介绍了光速是宇宙中已知最快的速度,并且我们通过光年这一单位来衡量巨大的天文距离。光在一年内可以行进约6万亿英里,称为一光年。举例说明了月球距离地球仅一光秒,而比邻星距离我们4.24光年,银河系直径约10万光年,仙女座星系距离我们约250万光年。接着,解释了天文学家如何通过三角视差法测量较近恒星的距离,以及对于更远的天体,如何使用标准烛光(如造父变星和Ia型超新星)来估算距离。强调了通过观测遥远天体,我们实际上是在回望宇宙的过去,从而帮助我们理解宇宙的历史和起源。
🌌 宇宙的信息传递
这段内容强调了宇宙不断地以光的形式向我们传递信息,而我们的任务是解码这些信息。这表明了天文学不仅仅是观测,还包括对观测数据的分析和理解,以便更好地认识宇宙及其运作原理。
Mindmap
Keywords
💡光速
💡光年
💡三角视差
💡标准烛光
💡造父变星
💡Ia型超新星
💡宇宙的尺度
💡宇宙的年龄
💡宇宙的信息
💡天文观测
💡宇宙的演化
Highlights
光是我们所知最快的事物。
光速之快,我们通过光行进的时间来测量巨大的距离。
光在一年内可以行进约6万亿英里,这个距离我们称之为一光年。
月球距离地球仅一光秒,而阿波罗宇航员需要四天时间才能到达。
最近的比邻星——普罗克西马半人马座,距离我们4.24光年。
我们的银河系大约有10万光年宽。
距离我们最近的仙女座星系大约有250万光年远。
空间是难以置信的广阔。
天体物理学家如何测量星星和星系的距离,尽管我们只能看到二维的视角?
对于非常近的天体,我们可以使用三角视差的概念。
通过观察星星在半年内(地球公转轨道的中点)的视位置变化,我们可以测量距离。
三角视差方法只适用于几千光年以内的天体。
对于超出我们星系的天体,我们使用标准烛光法。
标准烛光是我们知道其固有亮度或光度的天体。
造父变星是内部不稳定的特殊恒星,可以用作标准烛光。
通过比较观测到的光与计算出的固有亮度,我们可以确定恒星的距离。
Ia型超新星是另一种标准烛光,它们的亮度和衰减率之间的关系使我们能够测量数十亿光年外的距离。
观察遥远天体的重要性在于,光速使得宇宙成为一个内置的时间机器。
通过观察,我们能够回溯宇宙的历史,理解我们的起源。
宇宙不断地以光的形式向我们发送信息,我们需要解码这些信息。
Transcripts
Light is the fastest thing we know.
It's so fast that we measure enormous distances
by how long it takes for light to travel them.
In one year, light travels about 6,000,000,000,000 miles,
a distance we call one light year.
To give you an idea of just how far this is,
the Moon, which took the Apollo astronauts four days to reach,
is only one light-second from Earth.
Meanwhile, the nearest star beyond our own Sun is Proxima Centauri,
4.24 light years away.
Our Milky Way is on the order of 100,000 light years across.
The nearest galaxy to our own, Andromeda,
is about 2.5 million light years away
Space is mind-blowingly vast.
But wait, how do we know how far away stars and galaxies are?
After all, when we look at the sky, we have a flat, two-dimensional view.
If you point you finger to one star, you can't tell how far the star is,
so how do astrophysicists figure that out?
For objects that are very close by,
we can use a concept called trigonometric parallax.
The idea is pretty simple.
Let's do an experiment.
Stick out your thumb and close your left eye.
Now, open your left eye and close your right eye.
It will look like your thumb has moved,
while more distant background objects have remained in place.
The same concept applies when we look at the stars,
but distant stars are much, much farther away than the length of your arm,
and the Earth isn't very large,
so even if you had different telescopes across the equator,
you'd not see much of a shift in position.
Instead, we look at the change in the star's apparent location over six months,
the halfway point of the Earth's yearlong orbit around the Sun.
When we measure the relative positions of the stars in summer,
and then again in winter, it's like looking with your other eye.
Nearby stars seem to have moved against the background
of the more distant stars and galaxies.
But this method only works for objects no more than a few thousand light years away.
Beyond our own galaxy, the distances are so great
that the parallax is too small to detect with even our most sensitive instruments.
So at this point we have to rely on a different method
using indicators we call standard candles.
Standard candles are objects whose intrinsic brightness, or luminosity,
we know really well.
For example, if you know how bright your light bulb is,
and you ask your friend to hold the light bulb and walk away from you,
you know that the amount of light you receive from your friend
will decrease by the distance squared.
So by comparing the amount of light you receive
to the intrinsic brightness of the light bulb,
you can then tell how far away your friend is.
In astronomy, our light bulb turns out to be a special type of star
called a cepheid variable.
These stars are internally unstable,
like a constantly inflating and deflating balloon.
And because the expansion and contraction causes their brightness to vary,
we can calculate their luminosity by measuring the period of this cycle,
with more luminous stars changing more slowly.
By comparing the light we observe from these stars
to the intrinsic brightness we've calculated this way,
we can tell how far away they are.
Unfortunately, this is still not the end of the story.
We can only observe individual stars up to about 40,000,000 light years away,
after which they become too blurry to resolve.
But luckily we have another type of standard candle:
the famous type 1a supernova.
Supernovae, giant stellar explosions are one of the ways that stars die.
These explosions are so bright,
that they outshine the galaxies where they occur.
So even when we can't see individual stars in a galaxy,
we can still see supernovae when they happen.
And type 1a supernovae turn out to be usable as standard candles
because intrinsically bright ones fade slower than fainter ones.
Through our understanding of this relationship
between brightness and decline rate,
we can use these supernovae to probe distances
up to several billions of light years away.
But why is it important to see such distant objects anyway?
Well, remember how fast light travels.
For example, the light emitted by the Sun will take eight minutes to reach us,
which means that the light we see now is a picture of the Sun eight minutes ago.
When you look at the Big Dipper,
you're seeing what it looked like 80 years ago.
And those smudgy galaxies?
They're millions of light years away.
It has taken millions of years for that light to reach us.
So the universe itself is in some sense an inbuilt time machine.
The further we can look back, the younger the universe we are probing.
Astrophysicists try to read the history of the universe,
and understand how and where we come from.
The universe is constantly sending us information in the form of light.
All that remains if for us to decode it.
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