New Moon新月（初一）
Spring tide大潮
Sun and Moon on the same side of Earth, pulling along the same line.
日月在地球同一側，沿同一直線拉。
Astronomy · Lesson 4 · 天文教育 第四課
How Does the Moon Make the Tides?月亮怎麼造成潮汐？
Two bulges, two tides a day, and why new and full moons bring the biggest tides, on a real-time 3D Earth.
兩個鼓起、一天兩次滿潮，以及為什麼新月和滿月會漲大潮；3D 地球照真實時間運轉。
Big idea · 一句話看懂
The Moon pulls the near side of Earth harder than the far side, stretching the oceans into two bulges. Earth spins through them, so most coasts get two high tides a day.
月亮對地球近側的拉力比遠側大，把海水拉出兩個鼓起；地球自轉穿過這兩個鼓起，所以大多數海岸一天有兩次滿潮。
3D Model · 3D 模型
The Oceans on a Stretched Earth 被拉長的海洋
The blue shell is the ocean, stretched toward and away from the Moon. Press Play at 1 hour a second to watch Taiwan spin through both bulges, or at 2 days a second to watch the Sun and Moon line up for spring tides and pull apart for neap tides. Turn off the Sun's tide to see the Moon working alone.
藍色的殼是海水，被拉向月亮、也被拉向相反的一側。以「每秒 1 小時」播放，看台灣怎麼轉過兩個鼓起；以「每秒 2 天」播放，看日月排成一線時的大潮、互相垂直時的小潮。關掉「太陽的潮汐」，看月亮單獨的作用。
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 cards below still explain everything.
這個瀏覽器不支援 WebGL，無法顯示 3D 模型；下方的卡片一樣能看懂。
- Moon phase · 月相
- Today's tide · 今天的潮
- Sun–Moon angle · 日月夾角
- Tide size · 潮汐大小
- Moon's distance · 月地距離
⚠ Going to the tidal flats? · 要去潮間帶？Check the official tide forecast from the Central Weather Administration first, and leave well before high tide.出發前先查中央氣象署的潮汐預報，滿潮前提早離開。
- Blue shell: the ocean, with its tidal bulges drawn about a million times too tall
藍色殼：海水；潮汐鼓起放大了約一百萬倍 - Gold arrows: the tidal force, outward toward and away from the Moon, inward at the sides
金色箭頭：潮汐力，朝月亮與背向月亮向外、兩側向內 - Red dot: Changhua, turning with Earth
紅點：彰化，跟著地球自轉
Not to scale. The real tidal bulge in the open ocean is only about half a meter high, on a planet 12,700 km wide, so here it is exaggerated about a million times. The Moon is also drawn much too close and too big. The dates, the positions of the Sun and Moon, and Earth's spin are real.
未按比例：大洋中真實的潮汐鼓起只有約半公尺，而地球直徑有 12,700 公里，所以這裡放大了大約一百萬倍；月亮也畫得太近、太大。日期、日月的位置與地球自轉都是真實的。
Reading · 英文閱讀
4
Unit 4: How Does the Moon Make the Tides?
On the coast of Fangyuan in Changhua, farmers drive oxcarts out across the mudflats to tend their oyster beds, and a few hours later the same ground lies under the sea. Twice a day, almost everywhere on Earth, the ocean climbs up the shore and then pulls back again. These tides are so regular that they can be predicted years ahead. Nearly two thousand years ago, the Chinese thinker Wang Chong wrote that the rise of the tides follows the Moon. He was right.
在彰化芳苑的海邊，蚵農駕著牛車穿過泥灘去照顧蚵田；幾個小時後，同一片土地就沉到了海面下。地球上幾乎每個地方，海水一天兩次爬上岸邊、再退回去。潮汐規律到可以提前好幾年預測。將近兩千年前，中國思想家王充就寫下潮水的漲落跟著月亮走——他說對了。
The Moon's gravity pulls on every part of Earth, but not equally. The side of Earth facing the Moon is about 12,700 kilometers closer to it than the far side, so it is pulled a little harder, while the far side is pulled a little less than Earth as a whole. The result is a gentle stretch along the line to the Moon. The oceans, which are free to flow, pile up into two bulges: one on the side facing the Moon and one on the side facing away.
月亮的引力拉著地球的每一個部分，但拉得並不平均。地球面向月亮的一側，比背向的一側離月亮近了大約 12,700 公里，所以被拉得稍微用力一點；而遠側受到的拉力，則比整個地球平均的拉力小一點。結果就是沿著地月連線，地球被輕輕地拉長了。可以自由流動的海水因此堆成兩個鼓起：一個在面向月亮的一側，一個在背向月亮的一側。
Earth spins once a day underneath these two bulges, so most coasts pass through two high tides and two low tides each day. But the Moon also moves along its orbit, so Earth has to turn a little extra, about 50 minutes, to catch up with it. That is why high tide comes about 50 minutes later each day, just as the Moon rises about 50 minutes later each day.
地球每天在這兩個鼓起底下自轉一圈，所以大多數海岸每天會經過兩次滿潮、兩次乾潮。但月亮同時也沿著軌道往前走，地球得多轉一點點——大約 50 分鐘——才追得上它。這就是為什麼滿潮每天晚大約 50 分鐘，就像月亮每天晚大約 50 分鐘升起一樣。
The Sun raises tides too. It is far more massive than the Moon, but it is also about 400 times farther away, and the stretching effect weakens very quickly with distance. So the Sun's tides are a little less than half as strong as the Moon's. At new moon and full moon, the Sun, Earth, and Moon line up, the two tides add together, and we get extra-high and extra-low spring tides. The name has nothing to do with the season; it comes from the water springing up. At the first and last quarter, the Sun and Moon pull at right angles, partly canceling each other, and the difference between high and low tide is smallest. These are neap tides.
太陽也會引起潮汐。它的質量比月亮大得多，但距離也遠了約 400 倍，而這種拉長的效果會隨距離快速減弱，所以太陽的潮汐還不到月亮的一半。在新月和滿月時，太陽、地球、月亮排成一直線，兩股潮汐相加，就出現特別高、也特別低的大潮（spring tide）。這個英文名字跟春天無關，而是來自海水「湧起」（spring up）。在上弦和下弦時，太陽和月亮互相垂直地拉，部分抵銷，漲退的落差最小，這就是小潮（neap tide）。
Real coastlines make the picture more complicated. The shape of the sea floor and the coast can funnel the water and make the tides much bigger, or slow them down so that high tide arrives hours after the Moon passes overhead. In the Bay of Fundy in Canada, the water can rise and fall by more than 15 meters. In Taiwan, the tides along the west coast are much larger than on the east coast, which is why the mudflats of Changhua can stretch out for kilometers at low tide.
真實的海岸讓情況複雜得多。海底與海岸的形狀可以把海水像漏斗一樣匯集起來，讓潮汐變得大得多；也可以讓它慢下來，使滿潮在月亮經過頭頂好幾個小時之後才到。加拿大的芬迪灣，漲退落差可以超過 15 公尺。在台灣，西海岸的潮汐比東海岸大得多，這也是為什麼彰化的泥灘在退潮時可以延伸好幾公里。
The tides also have a slow, surprising effect on Earth and the Moon themselves. Water rubbing against the sea floor acts like a brake on Earth's spin, making each day about two thousandths of a second longer every century. In return, the Moon is slowly pushed away, by about 3.8 centimeters a year, which scientists measure by bouncing lasers off mirrors that astronauts left on the Moon. Long ago, Earth's pull raised tides in the Moon itself and slowed its spin until one side always faced us. It is the same face we saw in Lesson 1.
潮汐對地球和月亮本身，也有緩慢而驚人的影響。海水摩擦海底，就像在地球的自轉上踩了煞車，讓一天的長度每一百年變長大約千分之二秒。作為回報，月亮被慢慢推遠，每年大約 3.8 公分——科學家是用雷射打到太空人留在月球上的反射鏡來量的。很久以前，地球的引力也在月亮身上引起潮汐，把月亮的自轉拖慢，直到它永遠只有一面朝向我們——就是我們在第一課看到的那一面。
Read aloud · 課文朗讀
Questions · 閱讀理解
Why are there two tidal bulges instead of just one?
The Moon pulls the near side of Earth harder and the far side less than Earth as a whole, so Earth is stretched along the line to the Moon, and water piles up on both the near side and the far side.
Why does high tide come about 50 minutes later each day?
The Moon moves along its orbit while Earth spins, so Earth has to turn about 50 extra minutes each day to face the Moon again.
What is the difference between a spring tide and a neap tide?
Spring tides come at new and full moon, when the Sun and Moon line up and their tides add together. Neap tides come at the quarter moons, when they pull at right angles and partly cancel.
Words & Phrases · 生字及片語
regular(adj.)規律的Try to keep a regular bedtime, even on weekends.即使週末，也盡量保持規律的就寢時間。predict(v.)預測Weather apps can predict rain a few days ahead.天氣 App 可以提前幾天預測下雨。stretch(n.)拉伸；伸展Do a gentle stretch before you start running.開始跑步前，先輕輕做個伸展。bulge(n.)鼓起；隆起There was a bulge in his pocket where he kept his phone.他放手機的口袋鼓起了一塊。massive(adj.)質量大的；巨大的A massive truck blocked the narrow road.一輛巨大的卡車擋住了狹窄的道路。cancel out(phr. v.)抵銷The two forces cancel each other out, so the box does not move.兩個力互相抵銷，所以箱子不會動。funnel(v.)（像漏斗般）匯集The narrow valley funnels the wind into strong gusts.狹窄的山谷把風匯集成一陣陣強風。brake(n.)煞車She stepped on the brake when the light turned red.燈號變紅時，她踩了煞車。
Quick Check · 小測驗
1. What mainly causes the ocean tides?
2. About how many high tides do most coasts get each day?
3. When do spring tides happen?
4. Why are the Sun's tides weaker than the Moon's?
5. What is happening to the distance between Earth and the Moon?
Moon Phase and Tide · 月相與潮汐
Spring tides and neap tides 大潮與小潮
The biggest tides often come a day or two after new or full moon, because the oceans take time to respond.
最大的潮汐常常出現在新月或滿月之後一、兩天，因為海水需要時間反應。
First Quarter上弦（初八前後）
Neap tide小潮
Sun and Moon at right angles; their tides partly cancel.
日月互相垂直，兩股潮汐部分抵銷。
Full Moon滿月（十五前後）
Spring tide大潮
Sun and Moon on opposite sides, but still on one line. Both tides stretch Earth the same way.
日月在地球兩側，但仍在同一直線上，兩股潮汐朝同一方向拉長地球。
Last Quarter下弦（廿三前後）
Neap tide小潮
At right angles again; the smallest difference between high and low tide.
再次互相垂直，漲退落差最小。
Tide Words · 潮汐用語
Read a tide table in English 用英文看懂潮汐表
High tide滿潮
The moment the water is highest.
海水最高的時刻。
Low tide乾潮
The moment the water is lowest.
海水最低的時刻。
Flood tide漲潮
The water coming in, from low tide to high tide.
從乾潮到滿潮，海水湧進來。
Ebb tide退潮
The water going out, from high tide to low tide.
從滿潮到乾潮，海水退出去。
Tidal range潮差
The difference in height between high and low tide.
滿潮與乾潮的高度差。
Intertidal zone潮間帶
Shore that is underwater at high tide and dry at low tide.
滿潮時淹在水下、乾潮時露出的海岸。
Myth vs. Fact · 常見迷思
Four things people get wrong 四個常見的誤會
✗ Myth · 迷思There is only one bulge, on the side facing the Moon.只有一個鼓起，就在面向月亮的那一側。
✓ Fact · 事實There are two. The far side is pulled less than Earth as a whole, so it is left behind and bulges out too. That is why most coasts get two high tides a day, not one.有兩個。遠側受到的拉力比整個地球平均的小，被「留在後面」，也鼓了起來。所以大多數海岸一天有兩次滿潮，不是一次。
✗ Myth · 迷思High tide happens exactly when the Moon is overhead.月亮在頭頂正上方時，就是滿潮。
✓ Fact · 事實Coastlines and the sea floor slow the water down, so high tide often arrives hours later, and the delay is different at every port. Always check a real tide table.海岸與海底地形會拖慢海水，滿潮常常晚好幾個小時才到，而且每個港口的延遲都不一樣。一定要查真正的潮汐表。
✗ Myth · 迷思The Moon pulls harder at full moon.滿月時月亮拉得比較用力。
✓ Fact · 事實The Moon's pull has nothing to do with how much of it is lit. Spring tides come at both full and new moon because that is when the Sun and Moon line up. As Lesson 1 showed, the phase is only lighting.月亮的拉力跟它亮了多少無關。新月和滿月都有大潮，是因為那時日月排成一直線。第一課說過：月相只是光照的角度。
✗ Myth · 迷思Only the oceans have tides.只有海水才有潮汐。
✓ Fact · 事實The solid ground rises and falls too, by up to a few tens of centimeters twice a day. We cannot feel it because everything around us moves together.連堅硬的地面也會一天兩次上下起伏，最多可達幾十公分。我們感覺不到，是因為周圍的一切都一起在動。
Remember It · 記憶口訣
Tides in a sentence 一句話記住潮汐
Two bulges, two tides兩個鼓起，兩次滿潮
One bulge faces the Moon and one faces away. Earth turns through both every day, so most coasts get two high tides and two low tides.
一個鼓起朝向月亮，一個背向月亮；地球每天轉過兩個，所以大多數海岸一天有兩次滿潮、兩次乾潮。
Fifty minutes later every day每天晚大約 50 分鐘
High tide keeps time with the Moon, not the clock. If high tide is at noon today, expect it around 12:50 tomorrow.
滿潮跟著月亮走，不跟著時鐘走。今天中午滿潮，明天大約就是 12 點 50 分左右。
Big tides at new and full moon初一十五漲大潮
Spring tides come around the 1st and 15th of the lunar month; neap tides come around the 8th and 23rd.
大潮在農曆初一、十五前後；小潮在初八、廿三前後。這正是第一課的月相跟潮汐接上的地方。
Safety first on the tidal flats潮間帶，安全第一
On wide mudflats like Changhua's, the rising tide can come in faster than you can walk and fill channels behind you. Check the official tide forecast, leave well before high tide, and never go alone.
在彰化這樣廣闊的泥灘上，漲潮可能比人走路還快，還會先灌滿你身後的潮溝。出發前查官方潮汐預報、滿潮前提早離開、絕對不要單獨前往。
Classroom Activity 1 · 課堂活動一
Walk Like the Tide 用走路演出兩個鼓起
You need · 準備材料
- Three students standing in a line, about one step apart三位學生排成一列，相距約一步
- A fourth student to be the Moon, a few meters away第四位學生當月亮，站在幾公尺外
- Masking tape to mark the starting spots紙膠帶，標記起點
Steps · 步驟
- The three students in the line are the near side, the center, and the far side of Earth. Mark where each one stands.排成一列的三位學生，分別是地球的近側、中心和遠側。用膠帶標出每個人的位置。
- The Moon calls out "Pull!" The near student takes three steps toward the Moon, the center student two, and the far student one.月亮喊「拉！」近側的同學朝月亮走三步、中心的同學走兩步、遠側的同學走一步。
- Now look only from the center student's point of view. The near student has moved one step ahead, and the far student has fallen one step behind.現在只從中心同學的角度看：近側同學往前多走了一步，遠側同學則落後了一步。
- Ask: from the middle, which way did each friend move? Both moved away from you. That is the two bulges.問問大家：從中間看，兩位同伴往哪裡移動？都是離你而去——這就是兩個鼓起。
Teaching tip: this is the Why two bulges panel of the 3D model acted out. Switch the panel from Pull to Stretch after the activity.
教學提示：這正是 3D 模型裡「為什麼有兩個鼓起」小畫面的真人版。做完活動，再把小畫面從「引力」切到「拉伸」。
Classroom Activity 2 · 課堂活動二
A One-Week Tide Diary 一週潮汐日記
You need · 準備材料
- The official tide forecast for a nearby port, from the Central Weather Administration中央氣象署網站上，鄰近港口的潮汐預報
- A notebook or a shared spreadsheet筆記本或共用試算表
- A calendar that shows the Moon's phases標有月相的月曆
Steps · 步驟
- For seven days in a row, write down the times of the two high tides and the two low tides.連續七天，記下每天兩次滿潮、兩次乾潮的時間。
- Next to each day, draw the Moon's phase.在每一天旁邊畫上當天的月相。
- Find how much later the first high tide comes each day. Is it close to 50 minutes?算算每天第一次滿潮晚了多少分鐘，接近 50 分鐘嗎？
- Look at the tidal range. Does it grow toward new or full moon and shrink toward a quarter moon?看看潮差：接近新月或滿月時變大、接近上下弦時變小嗎？
Teaching tip: this works with English numbers and time expressions too. Have students report in full sentences, such as "High tide came 52 minutes later than yesterday."
教學提示：這也是練習英文數字與時間表達的好機會。請學生用完整句子報告，例如 "High tide came 52 minutes later than yesterday."