Every person who lives on this planet has seen a falling star,
also known as a shooting star.
I confess, I sincerely believed such was the case that
these were in fact stars, much like I believed in Santa Claus.
But then I heard the shocking truth–these are not in fact stars.
When peering into the sparkling emptiness of the night sky,
I watched as another meteoric body for the umpteen billionth of time,
try to ramp through the Earth’s atmosphere.
This happens constantly day in and day out.
Millions of cosmic bodies hurl themselves towards the surface of our planet everyday.
Really, there is nothing very special going on here.
So, despite the apparent absurdity of the phrase:
看啊 陨落的恒星 显然是荒唐的
look, look, a falling star!
it turns out that real falling stars do exist in our universe.
Fasten your seatbelts, ladies and gentlemen.
Once again we set off into deep space.
or, it is also called
a sizeable star. It is 700 times larger than the diameter of our Sun.
It is an even stranger and more surprising star than Betelgeuse,
the heroine from our last installment.
The first mention of this beauty is found in Hipparchus in 134 BC,
as well as in the testimonies of Chinese astronomers later in the year 1070.
But its almost supernatural properties were discovered only recently.
牧师 天文学家 大卫·法布里奇乌斯
Pastor, astronomer, David Fabricius,
quite by chance and without realizing it,
discovered a new type of star on the morning of August 13th,1596.
At that time, he was just watching Mercury.
Or rather, he was going to measure the angular distance
from the planet to the star glittering nearby
at an apparent magnitude of 3 in the constellation of Satis.
Interestingly, he had never come across it before,
and it was also notably absent from all the stellar maps and globes.
Though of course, maps and globes were not as accurate in ye olden days.
And the disregard for some not very bright star was commonplace.
Fabricius began to keep an eye on the stranger,
and lo and behold its brilliance grew right up to a magnitude of 2,
and it became the brightest star in its constellation by the end of that August.
But then in September, the star faded,
and by mid-October, it had disappeared completely.
In full confidence that this was a different new star,
Fabrizia stopped observing.
But to his great surprise, he came across this mysterious traveler,
thirteen years later on February 15th, 1609.
But to be fair, astronomer Johann Beier managed to notice it
about six years before this in 1603.
He entered the data into his famous star atlas,
but had not yet suspected these super properties of his five.
By the way, by that time, the star had already reached a stellar magnitude of 4.
Various astronomers from around the world began to closely monitor
Omicron Ceti for the next several decades.
So, for example, the Polish astronomer Jan Hevelius,
who observed the stellar body from 1659 to 1682,
称其为米拉 在拉丁文中解释为 令人惊叹的
called it Mira, which is from Latin, and translates as “amazing”.
And he was absolutely right, this star is amazing.
Usually, it is so dim that is quite diffcult to see with even a small amateur telescope.
但因为其独特性 它会在特定的时段 寒峰 里
But due to its peculiarity, it becomes the brightest star in the constellation Cetus
at certain times,the so-cold peak. Then it fades again
and becomes almost invisable,
and then it again and again and again, everything repeats.
Scientists finally, by the middle of the 17th century,
established that this miracle represented a new type of valuable star
with a very long period of brightness and a very large amplitude.
To put it simply, Mira is a star that constantly changes its brightness,
but it happens with a fair bit of irregularity.
The glitter of a star,
for those who do not know, is its apparent stellar magnitude, the same as luminosity,
或者更简单地说 辉度 代表了其亮度
or even simpler, brightness.
Using the astronomical scale, smaller numbers are brighter.
The brightness of Mira increases three and a half times
in just 332 days.
From a brightness of magnitude 10, when it is almost invisable in the telescope,
up to a magnitude of 2, when it becomes the brightest in its constellation.
正如我说过的 它的表现没有固定模式 事实上
As I said, there is no pattern to her behavior. As a matter of fact,
the period and range of brightness changes and is completely unstable.
One time, Omicron Ceti went from the relatively dark 9th magnitude,
and then increased to the 5th and then back again,
anther time she faded to the 10th magnitude
but then shut up to her maximum brightest magnitude of 2.
As you can see, the fluctuations in luminosity are simply immense.
But what does all this mean?
奥密克戎天体 亦称米拉 最暗时
The luminosity of Omicron Ceti aka Mira
at the minimum of its brightness almost corresponds,
or is even slightly less than the luminosity of our Sun.
That means then, that at the maximum, the brightness of Mira
will surpass that of our Sun by seven hundred times.
And sometimes, by as much as 1500 times the brightness of our Sun.
The whole point of this is this: when red giant pulsate, the temperature
of their surface also changes,
which immediately effects the optical properties of the stellar atmosphere;
as the temperature rises, the chemical compounds decompose,
and the atmosphere becomes more transparent.
Also, a considerable role is taken by hot hydrogen masses,
which erupt into the atmosphere during the periods of maximum brightness,
and further increase the brightness of the star. At least this is the most plausible explaination,
which I managed to unearth of the amazing changes that regularly occur with Mira Ceti.
And still, there is something more.
Scientists noticed in 1919
that a second spectrum was superimposed over the Mira sepctrum,
and it belongs to a very very hot white star,
A satellite was discovered very close to Mira four years later.
This hot little star is a white dwarf called Mira B,
which, by the way, literally feeds on its much larger neighbour.
Little Mira B orbits the giant Mira A only once every 400 years,
and therefore the satellite has made just one complete revolution around Mira A
since the time of Fabricius.
The average distance from the main star to the orbit of the white dwarf
is about 70 astronomical units.
That is to say,
70 times the average distance from the Earth to the Sun.
And the most interesting thing is that this little dwarf star has similar properties
to her much more voluptuous friend——the white dwarf also changes its brightness regularly.
But this happens for several other reasons.
Mira B has an accretion disk through which the white dwarf interacts with the main star,
sucking away stellar matter from her much larger sister.
Because of the unevenness of the supply of this substance,
the luminosity of the satellite also changes.
On average, the brightness value of the dwarf ranges from magnitude 12 to 9.5.
It should be noted that the measurement of changes in brightness
and stars of this type is a monumental amount of astronomical work.
Just imagine, in order to obtain the amplitude of oscillations of the luminosity of a star,
for a period of 13 years,
scientists need to take into account and superimpose all the fluctuations
星星的所有光的起伏变化和亮度 顺便提一句 这期间内
and the brightness of the star during this period. And their duration, by the way,
is measured in minutes. And finally, we come to our last couple of delicious tidbits.
The Galaxy Evolution Explorer satellite also known as the GALEX,
is an orbiting Ultraviolet Space Telescope launched in 2003.
The GALEX discovered a tail of matters stripped from the outer sphere of Mira A,
like that from a comet, a gigantic tail of material,
the length of which is about 13 light years.
So that you understand how long this really is, the distance from our Sun to the closest star
is about 4 light years. That’s a mighty long tail.
Most of the stars in our galaxy slowly rotate around the center,
moving about the same speed and the same direction as the interstellar gas.
In contrast to this, Mira is shooting through the galactic gas clouds
at the speed of 130 km a second.
As a result, the matter thrown out by Mira is simply blown back,
forming a bow wave tail of compressed gas.
As calculation show, every 10 years, the star drops a mass equivalent to that
of the entire Earth. To form such a tail, the star has taken
at least 30 thousand years. Oh, how I would like to see something like this up close.
It is a pity that I would need to be a god to make it happen.
A gigantic swelling located in front of the star is clearly visible in these pictures
from the Gale X Telescope. This is the region of the shockwave.
Something like this is formed in front of boat’s nose, when cutting through water at high speed.
又或者例如 当以超音速的速度移动时 产生在一颗子弹前
Or, for example, in front of a bullet, moving at supersonic speed.
This is matter thrown out by the star, experiencing a head-on collision
with particles of interstellar gas. And here my story comes to an end for today.
最后 我想补充一下 如此变化无常的星星我们已经在银河内
In conclusion, I should like to add that currently, we have discovered more than 46,000
such variable stars in the Milky Way and about 10,000 in other galaxies.
And this is only the beginning, as more are being discovered every year.
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