宇宙って聞くとちょっと難しそうに感じるかもしれないけど、実は僕たちの身の回りと深く関わってるんだ。太陽系は地球のお家みたいなもので、太陽を中心に8つの惑星がぐるぐる回ってる。
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Updated May 3, 2026
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太陽系の様々な天体について学ぼう
1 / 6
太陽系の基本と重要な用語
君たちが夜空を見上げたとき、あの光る点々にはそれぞれ名前と役割があるんだ。太陽系は太陽を中心にして、その重力で引きつけられた天体たちが集まってる範囲のこと。
恒星は自分で光や熱を出してる天体で、太陽がその代表例だよ。夜空で見える星のほとんどが恒星なんだ。惑星は恒星の周りを公転してる天体で、自分では光らないから太陽の光を反射して光って見える。
衛星は惑星の周りを回ってる天体で、地球の月が有名だね。公転は天体が別の天体の周りを回ること、自転は天体が自分の軸を中心に回転することだよ。地球の自転があるから昼と夜があるんだ。
覚えるコツ: 恒星は「自分で光る」、惑星は「恒星の周りを回る」、衛星は「惑星の周りを回る」って覚えよう！
惑星の分類：地球型と木星型
太陽系には8つの惑星があって、「すいきんちかもくどってんかい」で覚えられるよ。これらは特徴によって地球型惑星と木星型惑星の2つのグループに分けられるんだ。
地球型惑星（水星・金星・地球・火星）は太陽に近い内側にあって、サイズが小さくて密度が大きい。岩石や金属でできてるから重いんだ。衛星の数は少ないか全然ないよ。
木星型惑星（木星・土星・天王星・海王星）は太陽から遠い外側にあって、サイズが超大きいけど密度は小さい。主にガスや氷でできてるからふわっとしてる感じ。たくさんの衛星を持ってて、全部にリングがあるんだ。
テストポイント: 地球型は「小さい・硬い・重い」、木星型は「大きい・ガス・軽い」で覚えよう！
各惑星の特徴
それぞれの惑星には面白い特徴があるから、覚えやすいポイントで整理してみよう。
水星は大気がほとんどなくて昼夜の温度差が激しい。金星は二酸化炭素の厚い大気で温室効果がすごくて、水星より太陽から遠いのに表面温度が一番高いんだ。地球はもちろん水と大気があって生命が存在する特別な惑星。火星は表面が赤くて、極には氷がある。
木星は太陽系で最大の惑星で、ガスのしま模様と大赤斑が特徴的。土星は美しいリングを持ってて、密度が水より小さいから理論上は水に浮くよ。天王星は自転軸が横倒しになってる変わった惑星。海王星は太陽から最も遠くて青く見える。
小惑星は主に火星と木星の間にたくさんあって、彗星は氷やちりでできてて太陳に近づくと尾を出すんだ。
重要: 彗星の尾は常に太陽の反対方向を向く！これはテストでよく出るよ。
準惑星と太陽系小天体
冥王星って聞いたことあるでしょ？昔は9番目の惑星だったけど、今は準惑星って呼ばれてるんだ。惑星の定義には3つの条件があって、冥王星は「公転軌道に他の大きな天体がない」っていう条件を満たしてないから準惑星になったんだよ。
太陽系にはまだまだたくさんの天体があって、太陽系小天体って呼ばれてる。小惑星は主に火星と木星の間の「小惑星帯」にあって、岩石のかたまりみたいなもの。
彗星は「汚れた雪だま」って呼ばれることもあって、氷やちりでできてる。太陽に近づくと表面が溶けて美しい尾を作るんだ。この尾は太陽風の影響で、必ず太陽の反対側を向くよ。
覚えておこう: 冥王星が準惑星になった理由は、軌道上に同じような大きさの天体がたくさんあるから！
テスト対策のポイント
惑星の順番は絶対に覚えよう！「すいきんちかもくどってんかい」で水星から海王星まで完璧に言えるようになろう。
恒星・惑星・衛星の違いは図で書けるようにしておくこと。恒星は自分で光る太陽、惑星は太陽の周りを回る地球、衛星は惑星の周りを回る月って関係性を理解しよう。
地球型惑星と木星型惑星の特徴の違いは必ず出る問題だから、大きさ・密度・材料の3つのポイントで比較できるようにしておこう。内側の4つが地球型、外側の4つが木星型って覚えておけばOK。
注意: 夜空で明るく光ってる金星も、自分では光ってない！太陽の光を反射してるだけだから惑星なんだよ。
まとめ：太陽系マスターになろう
これで君も太陽系について基本的なことは理解できたはず！太陽という恒星を中心に8つの惑星が回ってて、それぞれに個性がある。
地球型と木星型の違い、各惑星の特徴、そして小惑星や彗星などの小天体まで、宇宙はとても面白い世界だよね。冥王星が準惑星になった理由も含めて、しっかり整理しておこう。
テストでは惑星の順番と分類、それぞれの特徴が必ず出るから、この内容をマスターすれば宇宙の問題は怖くない！夜空を見上げたとき、今度は違って見えるはずだよ。
最終確認: 惑星8個の順番、地球型と木星型の違い、恒星・惑星・衛星の定義、この3つが完璧なら準備万端！
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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4.6/5
App Store
4.7/5
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
太陽系の様々な天体について学ぼう
宇宙って聞くとちょっと難しそうに感じるかもしれないけど、実は僕たちの身の回りと深く関わってるんだ。太陽系は地球のお家みたいなもので、太陽を中心に8つの惑星がぐるぐる回ってる。
太陽系の基本と重要な用語
君たちが夜空を見上げたとき、あの光る点々にはそれぞれ名前と役割があるんだ。太陽系は太陽を中心にして、その重力で引きつけられた天体たちが集まってる範囲のこと。
恒星は自分で光や熱を出してる天体で、太陽がその代表例だよ。夜空で見える星のほとんどが恒星なんだ。惑星は恒星の周りを公転してる天体で、自分では光らないから太陽の光を反射して光って見える。
衛星は惑星の周りを回ってる天体で、地球の月が有名だね。公転は天体が別の天体の周りを回ること、自転は天体が自分の軸を中心に回転することだよ。地球の自転があるから昼と夜があるんだ。
覚えるコツ: 恒星は「自分で光る」、惑星は「恒星の周りを回る」、衛星は「惑星の周りを回る」って覚えよう！
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惑星の分類：地球型と木星型
太陽系には8つの惑星があって、「すいきんちかもくどってんかい」で覚えられるよ。これらは特徴によって地球型惑星と木星型惑星の2つのグループに分けられるんだ。
地球型惑星（水星・金星・地球・火星）は太陽に近い内側にあって、サイズが小さくて密度が大きい。岩石や金属でできてるから重いんだ。衛星の数は少ないか全然ないよ。
木星型惑星（木星・土星・天王星・海王星）は太陽から遠い外側にあって、サイズが超大きいけど密度は小さい。主にガスや氷でできてるからふわっとしてる感じ。たくさんの衛星を持ってて、全部にリングがあるんだ。
テストポイント: 地球型は「小さい・硬い・重い」、木星型は「大きい・ガス・軽い」で覚えよう！
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各惑星の特徴
それぞれの惑星には面白い特徴があるから、覚えやすいポイントで整理してみよう。
水星は大気がほとんどなくて昼夜の温度差が激しい。金星は二酸化炭素の厚い大気で温室効果がすごくて、水星より太陽から遠いのに表面温度が一番高いんだ。地球はもちろん水と大気があって生命が存在する特別な惑星。火星は表面が赤くて、極には氷がある。
木星は太陽系で最大の惑星で、ガスのしま模様と大赤斑が特徴的。土星は美しいリングを持ってて、密度が水より小さいから理論上は水に浮くよ。天王星は自転軸が横倒しになってる変わった惑星。海王星は太陽から最も遠くて青く見える。
小惑星は主に火星と木星の間にたくさんあって、彗星は氷やちりでできてて太陳に近づくと尾を出すんだ。
重要: 彗星の尾は常に太陽の反対方向を向く！これはテストでよく出るよ。
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準惑星と太陽系小天体
冥王星って聞いたことあるでしょ？昔は9番目の惑星だったけど、今は準惑星って呼ばれてるんだ。惑星の定義には3つの条件があって、冥王星は「公転軌道に他の大きな天体がない」っていう条件を満たしてないから準惑星になったんだよ。
太陽系にはまだまだたくさんの天体があって、太陽系小天体って呼ばれてる。小惑星は主に火星と木星の間の「小惑星帯」にあって、岩石のかたまりみたいなもの。
彗星は「汚れた雪だま」って呼ばれることもあって、氷やちりでできてる。太陽に近づくと表面が溶けて美しい尾を作るんだ。この尾は太陽風の影響で、必ず太陽の反対側を向くよ。
覚えておこう: 冥王星が準惑星になった理由は、軌道上に同じような大きさの天体がたくさんあるから！
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テスト対策のポイント
惑星の順番は絶対に覚えよう！「すいきんちかもくどってんかい」で水星から海王星まで完璧に言えるようになろう。
恒星・惑星・衛星の違いは図で書けるようにしておくこと。恒星は自分で光る太陽、惑星は太陽の周りを回る地球、衛星は惑星の周りを回る月って関係性を理解しよう。
地球型惑星と木星型惑星の特徴の違いは必ず出る問題だから、大きさ・密度・材料の3つのポイントで比較できるようにしておこう。内側の4つが地球型、外側の4つが木星型って覚えておけばOK。
注意: 夜空で明るく光ってる金星も、自分では光ってない！太陽の光を反射してるだけだから惑星なんだよ。
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まとめ：太陽系マスターになろう
これで君も太陽系について基本的なことは理解できたはず！太陽という恒星を中心に8つの惑星が回ってて、それぞれに個性がある。
地球型と木星型の違い、各惑星の特徴、そして小惑星や彗星などの小天体まで、宇宙はとても面白い世界だよね。冥王星が準惑星になった理由も含めて、しっかり整理しておこう。
テストでは惑星の順番と分類、それぞれの特徴が必ず出るから、この内容をマスターすれば宇宙の問題は怖くない！夜空を見上げたとき、今度は違って見えるはずだよ。
最終確認: 惑星8個の順番、地球型と木星型の違い、恒星・惑星・衛星の定義、この3つが完璧なら準備万端！
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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4.6/5
App Store
4.7/5
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE Knowunity AI. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user