1577 tycho pointed out that comets do not show different orientations from different places on the earth: therefore, he correctly concluded that they must be far away. Comets belong to small celestial bodies in the solar system.
Whenever a comet approaches the sun, its brightness will increase rapidly. Observations of comets that are quite far from the sun show that they move along a highly elongated ellipse, and the sun is located at a focus of this ellipse, which is consistent with Kepler's first law.
Comets spend most of their time away from the sun, where they are invisible. They can only be seen when they are near the sun.
There are about 40 comets whose period of revolution is quite short (less than 100 years), so they will appear one after another as the same celestial body. Halley's comet is the first celestial body observed in history. Newton's friend and donor Harley (1656- 1742) realized that it was periodic in 1705.
Its cycle is 76 years. Historical records show that it will be observed whenever it passes through the sun from 240 BC, possibly from 466 BC.
It was last adopted in 1986. The brightness of a comet is very low when it is far away from the sun, and its spectrum is simply the spectrum of reflected sunlight.
When the comet enters within 8 astronomical units from the sun, its brightness begins to increase rapidly and its spectrum changes dramatically. Scientists saw several bright spectral lines belonging to known molecules.
This change occurs because the solid matter (comet nucleus) that makes up a comet suddenly becomes hot enough to evaporate, and a gas cloud called coma surrounds the comet nucleus. The ultraviolet rays of the sun make this gas glow.
The diameter of coma is usually about 105 km, but the tail is often very long, reaching 108 km or 1 astronomical unit. Scientists estimate that comets usually only a few astronomical units away from the sun will disintegrate within thousands of years.
A.D. 1066, on the eve of Norman invasion of England, Comet Halley returned. At that time, people looked at this strange celestial body with a long tail in the night sky with mixed feelings and thought it was a war warning and omen given by God.
Later, Norman conquered England, and Commander Norman's wife embroidered the scene of Halley's Comet's return on the tapestry as a souvenir. China folks call comets "bad luck" and "disaster".
In this way, the appearance of comets is associated with human wars, famines, floods, plagues and other disasters. Comet is a small cloud-like celestial body with low mass, which orbits the sun in a flat orbit (very few in a near-circular orbit).
[Edit this paragraph] There are three kinds of orbits of comets: ellipse, parabola and hyperbola. Comets with elliptical orbits are also called periodic comets, and comets with other two orbits are also called aperiodic comets.
Periodic comets are divided into short-period comets and long-period comets. Generally speaking, a comet consists of a head and a tail.
The comet head includes two parts: the nucleus and the coma, and some have comet clouds. Not all comets have structures such as nucleus, coma and tail.
In ancient China, the shape of comets has been studied a lot. There are 29 pictures of comets on the silk book unearthed from Mawangdui ancient tomb in Changsha. It is clearly stated in Tian Wenzhi in the Book of Jin that comets don't shine because they reflect sunlight and are seen by us. Their tails are facing away from the sun.
Comets are huge, but their mass is pitifully small, even the mass of big comets is less than one tenth of that of the earth. Because a comet is composed of frozen impurities and dust, it is only a small cloud-like spot when it is far away from the sun; When it is close to the sun, the comet tail is produced because of the evaporation, gasification, expansion and eruption of the solidified body.
The tail is huge, hundreds of millions of kilometers long. It has different shapes, some more than one, and generally extends away from the sun, and the closer it is to the tail of the sun, the longer it is.
There are many comets in the universe, but only about 1600 has been observed so far. The orbit of a comet is very different from that of a planet. It is an extremely flat ellipse, and some even have parabolic or hyperbolic orbits.
Comets with elliptical orbits can return to the sun regularly, and such comets are called periodic comets. A comet with a parabolic or hyperbolic orbit can only approach the sun once in its life, and once it leaves, it will never come back. They are called aperiodic comets. These comets may not be members of the solar system, but passers-by from outside the solar system, inadvertently broke into the solar system, and then returned to the depths of the vast universe without hesitation. Periodic comets can be divided into short-period comets (period of revolution around the sun is less than 200 years) and long-period comets (period of revolution around the sun is more than 200 years).
The orbits of more than 600 comets have been calculated so far. The orbit of a comet may be affected by planets and changes.
When the comet is accelerated by the influence of the planet, its orbit will flatten, even become a parabola or hyperbola, thus making the comet leave the solar system; When the comet slows down, the eccentricity of the orbit will become smaller, which will make the long-period comet become a short-period comet, or even change from an aperiodic comet to a periodic comet and be "captured". [Edit this paragraph] The structure of a comet has no fixed volume and is very small when it is far from the sun; When approaching the sun, the coma becomes bigger and bigger, the tail becomes longer and the volume becomes very huge.
The longest tail can reach more than 200 million kilometers. The mass of comets is very small, and most of them are concentrated in the nucleus.
The average density of the nucleus is per cubic centimeter1g. The material in coma and tail is extremely thin, accounting for only 1%~5% of the total mass, or even less.
Comet material is mainly composed of water, ammonia, methane, cyanide, nitrogen, carbon dioxide and so on. The comet nucleus is a "dirty snowball" composed of water, carbon dioxide (dry ice), ammonia and dust particles condensed into ice. [Edit this paragraph] The tail is considered to be composed of gas and dust; Four combined effects blow it out of the comet: (1) the initial momentum obtained when gas and accompanying dust evaporate from the comet nucleus.
(2) The radiation pressure of sunlight pushes dust away from the sun. (3) The solar wind blows charged particles away from the sun.
(4) the attraction to the sun. The interaction of these effects makes each tail look different.
Of course, matter evaporates into the coma and tail, consuming the matter in the nucleus. Sometimes Comet Bila will explode.
2. Who has a composition about meteors and comets? At this moment, a meteor has just crossed the sky.
I miss you sitting under the eaves,
People say that the most beautiful love is like a meteor, short and brilliant. But after all, it's just a passer-by in life. It came when you didn't expect it, and when you marveled at it, it had left.
It turns out that you are a meteor in my life. The sudden appearance in my life caught me off guard, but I had to be surprised. Is it a gift from God? My life was lit up in an instant.
However, you left again. I'm still obsessed with that short-lived beauty.
Meteors are short-lived, so I have no time to savor them. You can only experience it slowly by leaving memories;
Meteor is brilliant. I am glad for its first appearance, but sad for its sudden departure.
If only life were like the first time.
If I have never been touched by you, I will not be heartbroken for you.
Meteor-like love never brought me warmth, but it brought me coolness. That coolness is the night wind, which blows my skirt, makes me grow lotus seeds step by step, blows my long hair and makes me feel like a fairy.
I looked up. Where are you?
The meteor streaked across the sky and disappeared without a trace. You have disappeared in my life, but my fingertips still can't help sticking out, trying to keep the last warmth.
Lower your head, and a tear will fall down your cheek.
From now on, don't look up to your light, don't pray for your love.
But why, my heart hurts?
Gradually, tears poured down.
In tears, I seem to see your face. Looking up, no, you stood me up and agreed to watch the meteor shower together.
Oh! Looking up hurriedly, a meteor flashed across the sky. It was a meteor shower!
I almost forgot that there will be a meteor shower tonight.
Beautiful meteor shower.
However, it is meaningless to just look at it. Or, leave.
Suddenly I felt a warmth coming from behind.
I froze: Is that you?
My name is Halley's Comet. I am a special star in the universe. People call me a comet.
After the British astronomer Halley discovered me, people called me Halley's comet again. I don't always like to stay in one place like an ordinary star. How lonely! I naturally like to travel in the sky, but I also have a certain route and go back to the sun to visit my relatives every 76 years.
Today, speaking of which, I am Halley's Comet. My head is called coma, and my hair is foggy coma.
Please don't laugh at me, I have a long tail behind me. The tail lasts short and the cough lasts long. It took twenty years for this sound to reach the tip of my tail.
My head is also surprisingly big, with a maximum diameter of 250 thousand kilometers. Although I am terribly big, there is nothing hard in my stomach. I am a visible and tangible big shot.
In the past, people thought my appearance was unlucky and purely superstitious. Don't believe that. Children, I want to make friends with you.
This year, we have met. When we meet again, you will all be grandparents. A brief comment on expository writing is a very practical style.
It plays an extremely important role in learning scientific and cultural knowledge, improving scientific and cultural level and promoting the progress of human civilization. Because explanatory writing is an article that introduces and explains things with explanation as the main expression.
Generally introduce the structure, category, origin, nature, practice, relationship and function of things, and explain the meaning, characteristics and evolution process of things. "My name is Halley's Comet" is an explanatory text that introduces the name origin, operation law and structure of Halley's Comet.
Requirements for general discussion: mainly introduce scientific knowledge, and be true and accurate. The young author carefully studied the knowledge about Halley's Comet, and then wrote his own understanding into the article, so the origin (because it was discovered by Harley in England), operation law (returning to the sun once every 76 years) and structure (coma, nucleus, long tail and big head) of Halley's Comet were all written accurately.
The language is easy to understand and easy for readers to accept and understand. This paper introduces the relevant knowledge of Halley's comet to readers by anthropomorphic method and first person method, which makes readers love reading and understand. Therefore, it is necessary to write a good expository article, pay attention to learning scientific knowledge, and flexibly use the learning writing methods, such as personification and imagination, so as to make the article both informative and interesting.
The knowledge about comets shows that the long, bright and sparse tail of comets gives people the impression that comets are very close to the earth, even in our atmosphere.
1577 tycho pointed out that comets do not show different orientations from different places on the earth: therefore, he correctly concluded that they must be far away. Comets belong to small celestial bodies in the solar system.
Whenever a comet approaches the sun, its brightness will increase rapidly. Observations of comets that are quite far from the sun show that they move along a highly elongated ellipse, and the sun is located at a focus of this ellipse, which is consistent with Kepler's first law.
Comets spend most of their time away from the sun, where they are invisible. They can only be seen when they are near the sun.
There are about 40 comets whose period of revolution is quite short (less than 100 years), so they will appear one after another as the same celestial body. Halley's comet is the first celestial body observed in history. Newton's friend and donor Harley (1656- 1742) realized that it was periodic in 1705.
Its cycle is 76 years. Historical records show that it will be observed whenever it passes through the sun from 240 BC, possibly from 466 BC.
It was last adopted in 1986. The brightness of a comet is very low when it is far away from the sun, and its spectrum is simply the spectrum of reflected sunlight.
When the comet enters within 8 astronomical units from the sun, its brightness begins to increase rapidly and its spectrum changes dramatically. Scientists saw several bright spectral lines belonging to known molecules.
This change occurs because the solid matter (comet nucleus) that makes up a comet suddenly becomes hot enough to evaporate, and a gas cloud called coma surrounds the comet nucleus. The ultraviolet rays of the sun make this gas glow.
The diameter of coma is usually about 105 km, but the tail is often very long, reaching 108 km or 1 astronomical unit. Scientists estimate that comets usually only a few astronomical units away from the sun will disintegrate within thousands of years.
A.D. 1066, on the eve of Norman invasion of England, Comet Halley returned. At that time, people looked at this strange celestial body with a long tail in the night sky with mixed feelings and thought it was a war warning and omen given by God.
Later, Norman conquered England, and Commander Norman's wife embroidered the scene of Halley's Comet's return on the tapestry as a souvenir. China folks call comets "bad luck" and "disaster".
In this way, the appearance of comets is associated with human wars, famines, floods, plagues and other disasters. Comet is a small cloud-like celestial body with low mass, which orbits the sun in a flat orbit (very few in a near-circular orbit).
[Edit this paragraph] There are three kinds of orbits of comets: ellipse, parabola and hyperbola. Comets with elliptical orbits are also called periodic comets, and comets with other two orbits are also called aperiodic comets.
Periodic comets are divided into short-period comets and long-period comets. Generally speaking, a comet consists of a head and a tail.
The comet head includes two parts: the nucleus and the coma, and some have comet clouds. Not all comets have structures such as nucleus, coma and tail.
In ancient China, the shape of comets has been studied a lot. There are 29 pictures of comets on the silk book unearthed from Mawangdui ancient tomb in Changsha. It is clearly stated in Tian Wenzhi in the Book of Jin that comets don't shine because they reflect sunlight and are seen by us. Their tails are facing away from the sun.
Comets are huge, but their mass is pitifully small, even the mass of big comets is less than one tenth of that of the earth. Because a comet is composed of frozen impurities and dust, it is only a small cloud-like spot when it is far away from the sun; When it is close to the sun, the comet tail is produced because of the evaporation, gasification, expansion and eruption of the solidified body.
The tail is huge, hundreds of millions of kilometers long. It has different shapes, some more than one, and generally extends away from the sun, and the closer it is to the tail of the sun, the longer it is.
There are many comets in the universe, but only about 1600 has been observed so far. The orbit of a comet is very different from that of a planet. It is an extremely flat ellipse, and some even have parabolic or hyperbolic orbits.
Comets with elliptical orbits can return to the sun regularly, and such comets are called periodic comets. A comet with a parabolic or hyperbolic orbit can only approach the sun once in its life, and once it leaves, it will never come back. They are called aperiodic comets. These comets may not be members of the solar system, but passers-by from outside the solar system, inadvertently broke into the solar system, and then returned to the depths of the vast universe without hesitation. Periodic comets can be divided into short-period comets (period of revolution around the sun is less than 200 years) and long-period comets (period of revolution around the sun is more than 200 years).
The orbits of more than 600 comets have been calculated so far. The orbit of a comet may be affected by planets and changes.
When the comet is accelerated by the influence of the planet, its orbit will flatten, even become a parabola or hyperbola, thus making the comet leave the solar system; When the comet slows down, the eccentricity of the orbit will become smaller, which will make the long-period comet become a short-period comet, or even change from an aperiodic comet to a periodic comet and be "captured". [Edit this paragraph] The structure of a comet has no fixed volume and is very small when it is far from the sun; When approaching the sun, the coma becomes bigger and bigger, the tail becomes longer and the volume becomes very huge.
The longest tail can reach more than 200 million kilometers. The mass of comets is very small, and most of them are concentrated in the nucleus.
The average density of the nucleus is per cubic centimeter1g. The material in coma and tail is extremely thin, accounting for only 1%~5% of the total mass, or even less.
Comet material is mainly composed of water, ammonia, methane, cyanide, nitrogen, carbon dioxide and so on. The comet nucleus is a "dirty snowball" composed of water, carbon dioxide (dry ice), ammonia and dust particles condensed into ice. [Edit this paragraph] The tail is considered to be composed of gas and dust; Four combined effects blow it out of the comet: (1) the initial momentum obtained when gas and accompanying dust evaporate from the comet nucleus.
(2) The radiation pressure of sunlight pushes dust away from the sun. (3) The solar wind blows charged particles away from the sun.
(4) the attraction to the sun. The interaction of these effects makes each tail look different.
Of course, matter evaporates into the coma and tail, consuming the matter in the nucleus. Sometimes it appears in an explosive way, such as comet Bila; .
5. Write an article about Polaris. I know that Polaris is the brightest star in the night sky in the northern hemisphere. Pearl-like sensibility naturally explains the ease of loneliness; Crystal clear and calm explains the nobility of faith. Looking back a thousand times, I appreciate its beauty! Frost and cold; Ice and snow are holy, and I still remember the firmness of the moment when the diamond melted. There is only one, no past, infinite emptiness, brilliance ... I found its purity in every touch! When there is no meteor falling, the attention is extraordinary; There is no spectacular excitement after the world of comets; Not to mention the colorful colors surrounding the rotation of the planet! Quietly, quietly, gently, quietly, it stays in the night sky in my heart, in the eternal universe ... Forgotten, or occasionally remembered? Constant, just the simplicity reflected in the hazy luster, that is the eternal ... constant mood, which also confirms our simple life! So, it embellished a piece of beauty, and I paid an eternity.
6. Write a composition and talk to the comet. One night, I had dinner with my parents. Suddenly, with a bang, there was no electricity! Is it a trip? Don't! The power went out. We had to stop eating and come to the balcony. : "wow! There are many stars in the sky. How beautiful! " I can't help being attracted by the stars in the sky. Mom also praised: "It's beautiful! I haven't seen so many stars for a long time! " Even my father was full of praise: "It's beautiful!"
Suddenly, we heard a loud cry: "Hey! How are you? " We looked at the sky and couldn't help being surprised. A big star is floating on our balcony. : "What star are you?" : "me? I am a special star in the universe. People call me a comet. Since the British astronomer Halley discovered me, people have called me Halley's Comet. "
I said, "Hello, Comet Halley! What are you doing here? " I don't always like to stay in one place like an ordinary star. How lonely! I am naturally fond of traveling in the sky. When I just passed your house, I found that the lights in this area suddenly went out, so I came to bring you a light. " I asked again, "What a coincidence!" He proudly said, "Yes! I only went back to the sun to visit my relatives once in 76 years. I caught it today. "
Why is your tail so long? The tail lasts short and the cough lasts long. It will take twenty years for this sound to reach the tip of my tail. : "Then why is your head so big?" I'm not ashamed to ask questions. "That's natural. It reaches 250,000 kilometers when the diameter is the largest. "
I said, "Halley's comet, you are so big!" " "Although I am very big, there is nothing hard in my stomach. I am a big shot who can't be seen or touched. People used to think my appearance was unlucky. Don't believe this purely superstitious idea. "
Halley's Comet said, "Son, I would like to be your friend." This year, we have met. When we meet again, you will all be grandparents. "
"Pa": "There is electricity again! Let's eat quickly! Goodbye! Halley's comet! "
7. The story of a comet hitting the earth took place in the summer of 2079 in London, the capital of England. People are wandering in the street, but they have no idea that a meteor group consisting of six meteors is moving towards them at a speed of 654.38+ million meters per second. Suddenly "whoosh-""Mao!" A meteor has just exploded in central London, and at this time, several major trouble spots in Britain have also been attacked by meteors. At this time, the British people were in a panic. With the approval of the United Nations, the British Prime Minister sent photos of the crater where the meteor fell to the Houston Space Center, the most advanced space center in the world.
After a preliminary understanding, these six meteors are some small rubble on a comet as big as California. That comet will collide with the earth in about fifteen days. If a comet hits the ocean, the water will get hot and cause a tsunami. Two-thirds of the people in the world will be burned to ashes by seawater, and the rest will freeze to death or starve to death because of hunger and cold. Humans will quit the earth, that is, the end of the world will come. . So the United Nations decided to send an arms expert, geologist Zhao Xiaodong and drilling expert Li Feiyu to drill a hole 800 feet deep on the comet (which happens to be the core of the comet) in an independent spacecraft, and then put 10,000 TNT nuclear bombs in the hole, so that the nuclear bombs exploded from the hole and the comet was blown in half, so that two pieces of the comet passed by the earth.
So at 5 o'clock in the morning, the spacecraft was launched! At 12: 30 this afternoon, we successfully reached the comet. At 5: 30 this afternoon, we drilled the hole, buried the nuclear bomb and prepared to leave the comet. What a coincidence, but at this moment, the problem came: our propeller was blocked by ice. This is not ordinary ice, but ice formed by a special plasma, which is incompatible with water and fire. At this time, some high-concentration sulfuric acid was sprayed into the ground to melt the ice. God helped me! But it also means that the comet's core begins to crack. Let's go, or we will die! We boarded the spaceship, slammed the acceleration button and the spaceship left the comet. In the sky, we detonated a nuclear bomb, "Boom!" There was a loud noise and the comet exploded. The shock wave made us feel the earth shaking.
History has written down our names, and we have become heroes among the world heroes!