New Moon新月（朔）
Not visible: it crosses the sky with the Sun, lost in its glare.
看不到：它和太陽一起走過天空，被陽光淹沒。
Astronomy · Lesson 1 · 天文教育 第一課
Why Does the Moon Change Shape?月亮為什麼會有圓缺？
The Moon is always half lit. What changes is how much of that lit half we can see — explore it in 3D.
月亮永遠是一半亮的，改變的只是我們看得到多少亮面。用 3D 模型親手轉轉看。
Big idea · 一句話看懂
The Sun always lights up half of the Moon. As the Moon circles Earth, we see more or less of that lit half. That is all a phase is.
太陽永遠照亮月亮的一半。月亮繞著地球轉，我們看到的亮面就時多時少——月相就只是這樣而已。
3D Model · 3D 模型
Sun, Earth, and Moon 日、地、月的相對位置
Drag the space view to turn it, and scroll or pinch to zoom. Press Play, drag the slider, or tap a phase. The panel beside it shows what the Moon looks like from Earth at that moment.
拖曳太空畫面可以旋轉視角，滾輪或雙指可以縮放。按「播放」、拖動滑桿或點選月相，旁邊的畫面就會顯示那一刻從地球看到的月亮。
Drag to turn · 拖曳旋轉 Scroll or pinch to zoom · 滾輪／雙指縮放
This 3D model needs WebGL, which this browser does not support. The phase cards below still explain everything.
這個瀏覽器不支援 WebGL，無法顯示 3D 模型；下方的月相卡片一樣能看懂。
- Yellow ring: the half lit by the Sun
黃色環：被太陽照亮的半面 - Teal ring: the half facing Earth
青色環：朝向地球的半面 - The shape we see is where the two halves overlap.
我們看到的月相，就是這兩個半面重疊的部分。
Not to scale. The Moon is really about 30 Earth-widths away, and the Sun is about 400 times farther than the Moon. The tilt of the Moon's orbit (really about 5°) is drawn larger so you can see it. Turn on True scale to see the real distance.
大小與距離未按比例：月亮其實在大約 30 個地球直徑之外，太陽又比月亮遠約 400 倍；月球軌道的傾斜（實際約 5°）也刻意畫大，讓你看得出來。打開「真實比例」可以看到真正的距離。
Reading · 英文閱讀
1
Unit 1: Why Does the Moon Change Shape?
Nearly a thousand years ago, the Song dynasty poet Su Shi wrote that people have their sorrows and joys, their partings and reunions, just as the Moon is sometimes hidden and sometimes bright, sometimes full and sometimes not. On Mid-Autumn night, families across Taiwan look up at a round, bright Moon. A week later, the same Moon looks like half a coin, and a week after that it seems to vanish from the sky. People have watched this cycle for as long as there have been people. The explanation is surprisingly simple, and it has nothing to do with the Moon itself changing shape.
將近一千年前，宋代詩人蘇軾寫下「人有悲歡離合，月有陰晴圓缺」。中秋夜，全台灣的家庭抬頭望著又圓又亮的月亮；一個星期後，同一個月亮看起來像半枚硬幣；再過一個星期，它好像從天空消失了。自有人類以來，人們就一直看著這個循環。它的道理其實出乎意料地簡單，而且跟月亮本身改變形狀一點關係也沒有。
The Moon makes no light of its own. Moonlight is really sunlight reflected off the Moon's gray, rocky surface. At every moment, the Sun lights up exactly one half of the Moon — the half that faces the Sun — while the other half stays dark. This is true on the night of a full moon, and it is just as true on a night when we cannot see the Moon at all. The Moon is always half lit. What changes is how much of that lit half we can see from Earth.
月亮自己不會發光。所謂月光，其實是太陽光照在月球灰色岩石表面後反射出來的光。任何時刻，太陽都剛好照亮月球的一半——朝向太陽的那一半——另一半則是暗的。滿月那晚是這樣，完全看不到月亮的那晚也一樣。月亮永遠是一半亮、一半暗；會改變的，是我們從地球上能看到那亮的一半有多少。
The Moon travels around Earth in an orbit, and as it moves, our view of its sunlit half keeps changing. When the Moon is between Earth and the Sun, its lit half faces away from us and we see almost nothing. This is the new moon. A few days later, a thin sliver of the lit half comes into view: a crescent. About a week after the new moon, we see exactly half of the disk lit. This phase is called the first quarter, because the Moon is a quarter of the way through its cycle. When Earth is between the Sun and the Moon, the whole lit half faces us, and we see a full moon. While the bright part is growing, we say the Moon is waxing; after the full moon it shrinks night by night, and we say it is waning. From one new moon to the next takes about 29.5 days.
月亮沿著軌道繞地球運行，它一移動，我們看到它亮面的角度就跟著改變。當月亮走到地球和太陽之間，亮的那一半背對著我們，我們幾乎什麼都看不到，這就是新月（朔）。幾天後，亮面的一小條細邊轉進視野，這就是眉月。新月後大約一週，我們看到月面剛好亮了一半，稱為上弦月——英文叫 first quarter，因為月亮這時走完了一個循環的四分之一。當地球位在太陽和月亮之間，整個亮面都朝向我們，就是滿月（望）。亮的部分一天天變大時，我們說月亮在「盈」（waxing）；滿月之後一夜一夜變小，就是「虧」（waning）。從一次新月到下一次新月，大約是 29.5 天。
Many people, including many adults, believe the phases are caused by Earth's shadow falling on the Moon. It is an easy mistake to make, but it cannot be right. Earth's shadow always points directly away from the Sun, so the only time it can reach the Moon is at full moon, when the Moon is on the far side of Earth. When that happens, we see a lunar eclipse, which comes only a few times a year at most and is over within hours. Most months, the Moon slips just above or below the shadow, because its orbit is tilted by about five degrees. And a crescent moon hangs near the Sun in the sky, nowhere near Earth's shadow.
很多人——包括很多大人——以為月相是地球的影子落在月亮上造成的。這個誤會很容易發生，但它不可能是對的。地球的影子永遠指向背對太陽的方向，所以它唯一能碰到月亮的時候，是月亮走到地球另一側的滿月時。真的碰到了，我們看到的是月食——一年最多只有幾次，而且幾個小時內就結束。大多數月份，月亮會從影子的上方或下方擦身而過，因為它的軌道傾斜了大約五度。何況眉月掛在天空中離太陽不遠的地方，跟地球的影子根本八竿子打不著。
Because the cycle is so regular, people have used the Moon as a calendar for thousands of years. The traditional Chinese calendar begins each month on the day of the new moon, which is why the Mid-Autumn Festival, on the fifteenth day of the eighth month, always comes near a full moon. The phases also tell you when to look up. A full moon rises around sunset and stays up all night. A first-quarter moon is already up in the afternoon, and a last-quarter moon rises around midnight and is still in the sky the next morning. So the Moon is not only a nighttime object. This week, try looking for it in daylight.
因為這個循環非常規律，幾千年來人們一直把月亮當成日曆。傳統農曆把每個月的第一天訂在新月（朔）那天，所以農曆八月十五的中秋節，永遠落在滿月前後。月相也告訴你什麼時候該抬頭看。滿月大約在日落時升起，整夜都在天上；上弦月下午就已經升上天空；下弦月大約半夜才升起，到隔天早上都還看得到。所以月亮不只是晚上的東西——這個星期，試著在白天找找看它吧。
Read aloud · 課文朗讀
Questions · 閱讀理解
Why is the Moon always "half lit," even on a night when we cannot see it?
Because the Sun always shines on the half of the Moon that faces it. The Moon's position only changes how much of that lit half is turned toward Earth.
Where is the Moon at new moon, and why can't we see it then?
It is between Earth and the Sun, so its lit half faces away from us and the side facing Earth is dark. It is also in the sky with the Sun, lost in its glare.
Give two reasons why Earth's shadow cannot be what causes the Moon's phases.
Earth's shadow points away from the Sun, so it can only reach the Moon at full moon, and when it does we see a lunar eclipse, not a phase. Also, a crescent moon appears close to the Sun in the sky, far from Earth's shadow.
Words & Phrases · 生字及片語
reflect(v.)反射；映照A calm lake reflects the mountains like a mirror.平靜的湖面像鏡子一樣映照出群山。orbit(n.)軌道；繞行The space station completes one orbit of Earth about every 90 minutes.太空站大約每 90 分鐘繞地球一圈。phase(n.)（月）相；階段The project is now in its final phase.這個計畫現在進入最後階段。crescent(n.)新月形；眉月The croissant gets its name from its crescent shape.可頌（croissant）的名字就來自它的新月形狀。sliver(n.)細條；一小片Only a sliver of light came through the curtains.只有一絲細細的光從窗簾縫透進來。wax and wane(v.)（月亮）盈虧；時盛時衰Interest in the hobby tends to wax and wane with the seasons.大家對這個嗜好的熱度，往往隨季節時高時低。eclipse(n.)（日、月）食Thousands of people traveled to see the total solar eclipse.成千上萬的人遠道而來觀看日全食。tilted(adj.)傾斜的The picture on the wall is slightly tilted to the left.牆上那幅畫稍微往左歪了。
Quick Check · 小測驗
1. Where does moonlight come from?
2. How much of the Moon is lit by the Sun at any moment?
3. Why is it called the "first quarter" when we see half of the Moon lit?
4. What do we see when Earth's shadow falls on the Moon?
5. Which moon rises around sunset and stays up all night?
The Eight Phases · 月相八態
One cycle, about 29.5 days 一個循環，約 29.5 天
Directions and "right/left" are for the Northern Hemisphere, where Taiwan is. Times are rough: the real times shift by an hour or more with the seasons.
方向與左右以北半球（台灣所在）為準。時間只是大概，實際會隨季節前後差一個小時以上。
Waxing Crescent眉月
Low in the west just after sunset.
日落後不久，低掛在西方天空。
First Quarter上弦月
Afternoon and evening; sets around midnight. The right half is lit.
下午到上半夜，約午夜落下。右半邊亮。
Waxing Gibbous盈凸月
From late afternoon until after midnight.
傍晚前升起，一直到過了午夜。
Full Moon滿月（望）
All night long: rises at sunset, sets at sunrise.
整夜可見：日落時升起，日出時落下。
Waning Gibbous虧凸月
From mid-evening into the next morning.
晚上九點左右升起，一直到隔天早上。
Last Quarter下弦月
After midnight and in the morning sky. The left half is lit.
下半夜到早上都看得到。左半邊亮。
Waning Crescent殘月
Low in the east before dawn.
黎明前，低掛在東方天空。
Myth vs. Fact · 常見迷思
Four things people get wrong 四個常見的誤會
✗ Myth · 迷思The phases are caused by Earth's shadow.月相是地球的影子造成的。
✓ Fact · 事實Earth's shadow can only reach the Moon at full moon, and then it makes a lunar eclipse, not a phase. Turn on "Earth's shadow" in the model and watch where it points.地球的影子只有在滿月時才可能落到月亮上，那時造成的是月食，不是月相。在模型裡打開「地球的影子」，看看它指向哪裡。
✗ Myth · 迷思The Moon only comes out at night.月亮只有晚上才出來。
✓ Fact · 事實For about half of every month, the Moon is up in daylight too. A first-quarter moon is easy to spot in the afternoon.每個月大約有一半的日子，白天也看得到月亮；上弦月在下午就很容易找到。
✗ Myth · 迷思The far side of the Moon is always dark.月球背面永遠是黑的。
✓ Fact · 事實The far side gets just as much sunlight as the near side; at new moon it is fully lit. We never see it only because the Moon turns exactly once for every trip around Earth, so the same face always points at us.月球背面照到的陽光跟正面一樣多，新月時背面甚至是全亮的。我們看不到它，只是因為月亮每繞地球一圈剛好自轉一圈，永遠同一面朝向我們。
✗ Myth · 迷思People in other countries see a different phase tonight.別的國家今晚看到的是不同的月相。
✓ Fact · 事實Everyone on Earth sees the same phase at the same time. In the Southern Hemisphere, though, the Moon looks upside down, so a waxing moon is lit on the left. Try the "Southern Hemisphere" switch.同一時間，全世界看到的月相都一樣。不過在南半球，月亮看起來是上下顛倒的，所以漸盈的月亮是左邊亮。試試模型裡的「南半球」開關。
Remember It · 記憶口訣
Read the Moon at a glance 一眼看懂月亮
One rule that always works永遠適用的一條規則
The lit side of the Moon always points toward the Sun. It works in any country, at any hour, in either hemisphere.
月亮的亮面永遠朝向太陽。不管在哪個國家、幾點鐘、南半球還是北半球，都成立。
The Chinese rhyme中文口訣：上上上西西，下下下東東
First quarter (上弦): first half of the lunar month, first half of the night, western sky, western half lit. Last quarter (下弦): the second half of each, and east instead of west.
上弦月：農曆上半月、上半夜看得到、在西邊天空、西半邊亮。下弦月：農曆下半月、下半夜看得到、在東邊天空、東半邊亮。
D-O-C英文口訣 D-O-C
In the Northern Hemisphere the Moon grows like a D, is full like an O, and shrinks like a C. Flip it in the Southern Hemisphere.
在北半球，月亮變大時像 D、滿月像 O、變小時像 C；到了南半球要反過來。
Why Taiwan's crescent smiles為什麼台灣的眉月像在微笑
Near the tropics, and Taiwan sits right on the Tropic of Cancer, a crescent low in the sky often lies on its back like a smile or a little boat. Farther north, it stands up more like a D or a C.
在熱帶附近（台灣就在北回歸線上），貼近地平線的眉月常常像躺著的微笑或小船；越往北走，它就越像立起來的 D 或 C。
Classroom Activity · 課堂活動
Be the Earth: A Lamp-and-Ball Moon 你就是地球：燈泡與小球的月相實驗
You need · 準備材料
- A lamp with the shade removed (the Sun)一盞拿掉燈罩的檯燈（太陽）
- A white foam ball stuck on a pencil (the Moon)插在鉛筆上的白色保麗龍球（月亮）
- Your own head (Earth)你自己的頭（地球）
- A room you can make dark一間可以關燈的教室
Steps · 步驟
- Turn off the room lights and stand a few steps from the lamp. Hold the ball at arm's length, a little higher than your head.關掉教室的燈，站在離檯燈幾步遠的地方。手臂伸直拿著小球，比頭稍微高一點。
- Face the lamp with the ball in front of it. You see only the dark side: a new moon.面向檯燈，讓小球擋在燈前面：你只看到暗的一面——這是新月。
- Keep your eyes on the ball and turn slowly to your left. A crescent appears on its right edge, then a half, then more.眼睛盯著小球，慢慢向左轉。右邊先出現一道細細的眉月，接著是半個，然後越來越多。
- With your back to the lamp (hold the ball above your head's shadow), you see a full moon. Keep turning and watch it wane.背對檯燈時（讓小球高過頭的影子），你看到的是滿月。繼續轉，看它一點一點虧下去。
- Ask yourself: was the ball ever not half lit? What really changed?問問自己：小球有哪一刻不是一半亮的嗎？真正改變的是什麼？
Teaching tip: before each quarter turn, have students predict what they will see. If a head shadow falls on someone's ball, stop and point it out: that is a lunar eclipse.
教學提示：每轉四分之一圈前，先讓學生預測會看到什麼。如果有人的頭影剛好遮到小球，停下來告訴大家：這就是月食。