Astronomy · Lesson 5 · 天文教育 第五課
Real stars on a 3D sky, Earth's night side pointing at a new part of space each season, and tonight's sky over Changhua.
真實亮星組成的 3D 天球：地球的夜側每一季對著不同方向的星空；再看看今晚彰化的天上有什麼。
At night we look out from the side of Earth that faces away from the Sun. As Earth travels around the Sun, that night side points toward different stars, so each season has its own constellations.
夜晚，我們是從地球背對太陽的那一側往外看。地球繞著太陽走，這一側就對著不同的星星，所以每個季節都有自己的星座。
3D Model · 3D 模型
The teal arrow points out from Earth's night side. The constellations near its tip are up all night; the ones behind the Sun are lost in daylight. Press Play at 5 days a second and watch the arrow sweep around the sky in a year. The chart on the right is the sky over Changhua at the same moment. Switch to 1 hour a second to watch one night go by.
青綠色箭頭從地球的夜側指出去：箭頭附近的星座整夜可見，太陽背後的星座則被陽光淹沒。用「每秒 5 天」播放，看箭頭一年掃過整片星空；右邊是同一時刻彰化上空的星圖。切到「每秒 1 小時」，看一個晚上星星怎麼移動。
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 sky chart and the cards below still work.
這個瀏覽器不支援 WebGL，無法顯示 3D 模型；星空圖與下方的卡片一樣能用。
Not to scale. The stars are drawn on a sphere only about 21 times wider than Earth's orbit; real stars are hundreds of thousands of times farther away, so their directions barely change as Earth moves. Earth and the Sun are drawn far too big. The stars, their positions and brightness, the dates, and Earth's orbit and spin are real.
未按比例：星星畫在只比地球軌道大約 21 倍的球面上；真實的星星遠了幾十萬倍以上，所以地球在軌道上移動時，看星星的方向幾乎不變。地球和太陽也畫得太大。星星的位置與亮度、日期、地球的公轉與自轉都是真實的。
Stars: Yale Bright Star Catalogue, 5th ed. (Hoffleit & Warren, 1991; public domain), 1,634 stars brighter than magnitude 5. Constellation lines and Chinese star groups drawn by twrses.org; the constellation the Sun is in follows the IAU constellation boundaries. Planets are not shown.
星表：耶魯亮星星表第五版（公有領域），亮於 5 等的 1,634 顆星。星座連線與中國星官為本站自繪；太陽在哪個星座依 IAU 星座邊界判斷。圖中不含行星。
Reading · 英文閱讀
On a winter evening in Taiwan, Orion stands high in the south, with the three stars of his belt in a neat row. Look for him on a summer evening, and he is gone. In his place, the curling tail of Scorpius hangs low over the southern horizon, with the red star Antares at its heart. About 1,300 years ago, the poet Du Fu wrote that friends who never meet are like Shen and Shang, two groups of stars that are never in the sky together. Shen is the Chinese name for Orion's main stars, and Shang is Antares. Why do they take turns like that?
First, the stars never go away. They are in the sky during the day as well, but sunlight scattered by the air makes the daytime sky so bright that it hides them. Night is simply the side of Earth that faces away from the Sun. When your part of the world turns into that side, the glare is gone, and you can finally see out into space. So the stars you see at midnight are the stars in the direction opposite the Sun.
Earth also travels around the Sun, once a year. As it moves along its orbit, the night side points in a slowly changing direction, about one degree a day. In winter, it faces the part of space where Orion is. Six months later, Earth is on the other side of the Sun. Now the night side faces Scorpius, while Orion lies behind the Sun, lost in daylight. The stars have not moved; we have. The constellations along the Sun's yearly path are called the zodiac constellations, and the Sun passes in front of a new one about every month.
You can notice this shift a little every night. A star rises about four minutes earlier each evening. That adds up to about two hours a month, so a star that rises at 11 p.m. this month rises around 9 p.m. next month. After a full year, Earth is back where it started, and the same stars return at the same time of night. That is why farmers in ancient China and Egypt could use the stars as a calendar, telling them when to plant and when to expect the rains or the floods.
Different cultures connected the same stars into different pictures. The constellations astronomers use today come mostly from ancient Greece. Ancient Chinese astronomers divided the sky into the Three Enclosures around the North Pole and the Twenty-Eight Lunar Mansions along the path of the Moon. The two stars in the story of the Cowherd and the Weaver Girl, Altair and Vega, sit on either side of the Milky Way, the "Silver River." They shine high overhead on summer evenings, around the time of the Qixi Festival on the seventh day of the seventh lunar month.
A constellation is a pattern, not a family. Its stars only look close together because they lie in the same direction. Betelgeuse, Orion's red shoulder, is roughly 550 to 700 light-years away, while Rigel, his bright foot, is about 860 light-years away. The light you see from Betelgeuse tonight left it at least 500 years ago, during the Ming dynasty or even earlier. Stars do drift, but so slowly that the constellations will look the same for your whole life. So step outside tonight and look up: the sky you see belongs to this season.
Questions · 閱讀理解
Why can't we see the stars during the day?
Why is Orion easy to see on winter evenings but not on summer evenings?
About how much earlier does a star rise each month, and why?
Words & Phrases · 生字及片語
Quick Check · 小測驗
1. Why do we see different constellations in different seasons?
2. Where are the stars during the daytime?
3. About how much earlier does a star rise each night?
4. In Du Fu's poem, Shen and Shang are...
5. Why do the stars of a constellation look close together?
Four Seasons of Stars · 四季星空
These are the skies over Changhua at 9 p.m. The same stars come back earlier in the night as the months go by, so the "summer" stars are also up before dawn in spring.
以上是彰化晚上九點的星空。隨著月份推進，同樣的星星會在夜裡越來越早出現；所以「夏季」的星星，春天清晨天亮前就看得到。
The brightest sky of the year. Find the Winter Triangle: Betelgeuse, Sirius, and Procyon.
一年中最燦爛的星空。找找冬季大三角：參宿四、天狼星、南河三。
Follow the curve of the Big Dipper's handle: arc to Arcturus, then speed on to Spica.
順著北斗七星斗柄的弧線：先畫到大角星，再一路延伸到角宿一。
The Summer Triangle is high overhead. Far from city lights, the Milky Way runs from Cygnus down to Sagittarius.
夏季大三角高掛頭頂。遠離城市燈光時，銀河從天鵝座一路流到人馬座。
A quiet sky with few bright stars. Fomalhaut sits alone in the south, and the Summer Triangle is still setting in the west.
亮星不多的安靜星空。北落師門孤單地掛在南方，夏季大三角還在西邊慢慢落下。
Tonight · 今晚
Calculated in your browser for today at 9 p.m. Hold your fist at arm's length: one fist is about 10 degrees. A very bright "star" that is not on this list is probably a planet.
依今天晚上九點，在你的瀏覽器裡現算。手臂伸直握拳：一個拳頭大約是 10 度。如果看到一顆很亮、卻不在清單上的「星」，多半是行星。
Calculating… · 計算中…
East and West · 東西方的星空
Turn on Chinese star groups in the 3D model to see the Chinese pictures drawn over the Western ones.
打開 3D 模型的「中國星官」，就能看到中國星圖疊在西方星座上的樣子。
參商 · Shen and Shang
人生不相見，動如參與商。——杜甫〈贈衛八處士〉"In life we seldom meet, just like Shen and Shang." (Du Fu, To the Hermit Wei Ba)
Shen is Orion's main stars, and Shang is Antares in Scorpius. They sit almost opposite each other in the sky, so one is rising about when the other is setting. The Zuo Zhuan, a history more than 2,000 years old, tells of two quarreling brothers who were sent to live far apart, one to watch Shang and the other to watch Shen.
參是獵戶座的主要亮星，商是天蠍座的心宿二。它們在天上幾乎正對面，一個升起時，另一個差不多正要落下。兩千多年前的《左傳》記載，高辛氏的兩個兒子閼伯與實沈天天爭吵，只好被分開：一個去主管商星，一個去主管參星。
七夕 · Qixi
Altair, the Cowherd, and Vega, the Weaver Girl, sit on either side of the Milky Way. In the legend, magpies build a bridge so they can meet once a year on Qixi. In reality they are about 15 light-years apart, so even a message sent at the speed of light would take 15 years to arrive.
牛郎星（河鼓二）和織女星隔著銀河相望。傳說每年七夕，喜鵲搭起鵲橋讓他們相會。實際上兩顆星相距大約 15 光年，就算用光速傳訊息，也要走 15 年。
四象 · Four Symbols
The Moon takes about 27 days to go once around the sky, so Chinese astronomers marked 28 "mansions" where it stays night after night. Seven mansions make each of four animals: the Azure Dragon of the east, the Black Tortoise of the north, the White Tiger of the west, and the Vermilion Bird of the south. Shen belongs to the White Tiger, and Antares is the Dragon's heart.
月亮大約 27 天在天上繞一圈，古人就沿著它的路線劃出 28 個「宿」，像是月亮每晚住宿的地方。每七宿組成一隻神獸：東方青龍、北方玄武、西方白虎、南方朱雀。參宿屬於白虎，心宿二就是青龍的心臟。
三垣 · Three Enclosures
Around the North Pole lies the Purple Forbidden Enclosure, the emperor's palace in the sky; Beijing's Forbidden City is named after it. The Supreme Palace Enclosure is the government, and the Heavenly Market Enclosure is a busy marketplace. In all, the traditional Chinese sky has 283 star groups, while astronomers today divide the sky into 88 constellations.
北極周圍是紫微垣，天帝的宮殿，北京的紫禁城就是照它命名；太微垣是朝廷，天市垣是熱鬧的市集。傳統中國星空一共有 283 個星官，而現代天文學把天空分成 88 個星座。
| Western name · 西方名稱 | Chinese name · 中國星名 | Why it matters · 小故事 |
|---|---|---|
| Betelgeuse (Orion)獵戶座 α | 參宿四Shen, fourth star | A red supergiant, one of the Shen stars.紅超巨星，參宿的一員。 |
| Antares (Scorpius)天蠍座 α | 心宿二（大火）Heart, second star; the Great Fire | "The Fire flows down in the seventh month" in the Book of Songs: it sinks in the west as summer ends.《詩經》「七月流火」：大火星往西沉，天氣就要轉涼。 |
| Vega (Lyra)天琴座 α | 織女星（織女一）The Weaver Girl | High overhead on summer evenings.夏夜高掛頭頂。 |
| Altair (Aquila)天鷹座 α | 牛郎星（河鼓二）The Cowherd | Across the Milky Way from Vega.在銀河另一岸與織女星相望。 |
| Sirius (Canis Major)大犬座 α | 天狼星The Celestial Wolf | The brightest star at night. Su Shi wrote of drawing his bow to shoot the Wolf.夜空最亮的恆星。蘇軾：「會挽雕弓如滿月，西北望，射天狼。」 |
| Spica (Virgo)室女座 α | 角宿一Horn, first star | The Dragon's horn, first of the 28 mansions.青龍的角，二十八宿的第一宿。 |
| Big Dipper (Ursa Major)大熊座 | 北斗七星The Northern Dipper | Its handle points east on spring evenings. More in Lesson 6.「斗柄東指，天下皆春」，下一課再細說。 |
| Canopus (Carina)船底座 α | 老人星The Old Man Star | A symbol of long life, low in the south on winter evenings in Taiwan.象徵長壽的南極仙翁；台灣冬夜低掛南方地平線上。 |
Myth vs. Fact · 常見迷思
✗ Myth · 迷思The stars disappear during the day.白天星星就不見了。
✓ Fact · 事實They are always there. Sunlight scattered by the air lights up the whole sky and hides them. During a total solar eclipse, when the Sun is covered, bright stars appear in the middle of the day.星星一直都在。陽光被空氣散射，照亮整片天空，把星星蓋住了。日全食時太陽被遮住，大白天也看得到亮星。
✗ Myth · 迷思The constellations change with the seasons because the stars move.星座隨季節改變，是因為星星在移動。
✓ Fact · 事實The stars stay put; Earth moves. As it goes around the Sun, our night side faces a different direction. The stars do drift, but so slowly that Orion looks almost exactly the way it did for Du Fu.星星沒動，是地球在動：地球繞太陽走，夜側就對著不同方向。星星其實也在移動，只是慢到我們今天看到的獵戶座，跟杜甫當年看到的幾乎一模一樣。
✗ Myth · 迷思The stars in a constellation are close to each other.同一個星座的星星彼此靠得很近。
✓ Fact · 事實They only lie in the same direction. Rigel is about 860 light-years away, but Bellatrix, Orion's other shoulder, is only about 250. Seen from another star, Orion would not look like a hunter at all.它們只是在同一個方向上。參宿七大約 860 光年遠，獵戶座的另一個肩膀參宿五卻只有約 250 光年。從別的恆星看過來，獵戶座根本不像個獵人。
✗ Myth · 迷思On your birthday, the Sun is in front of your horoscope sign.生日那天，太陽就在你的星座前面。
✓ Fact · 事實Usually it is not. The horoscope signs were fixed about 2,000 years ago, and Earth's slow wobble has shifted the sky by almost a whole constellation since then. On October 1 the sign is Libra, but the model shows the Sun in front of Virgo. The Sun also passes through Ophiuchus, a 13th constellation that horoscopes leave out.通常不是。星座運勢的「星座」是大約兩千年前定下的，地軸緩慢的晃動（歲差）讓天空至今偏移了將近一整個星座。10 月 1 日在運勢上是天秤座，模型裡的太陽卻在室女座前面。太陽還會經過運勢裡沒有的第 13 個星座：蛇夫座。
Remember It · 記憶口訣
A star rises about 4 minutes earlier each night. If Orion rises at 11 p.m. tonight, a month from now it will rise around 9 p.m.
同一顆星每晚大約提早 4 分鐘升起。如果今晚獵戶座 11 點升起，一個月後大約 9 點就升起了。
Orion and Scorpius sit almost opposite each other in the sky, so they take turns: the Shen and Shang of Du Fu's poem.
獵戶座和天蠍座在天上幾乎正對面，只能輪流登場，這就是杜甫詩裡的參與商。
Whatever constellation is opposite the Sun is up all night. In early October the Sun is in Virgo, so Pisces, across the sky, is up from dusk to dawn.
跟太陽正對面的星座整夜可見。十月初太陽在室女座，對面的雙魚座就從黃昏一直掛到天亮。
Winter: Betelgeuse, Sirius, Procyon. Spring: Arcturus, Spica, Denebola. Summer: Vega, Altair, Deneb. Autumn has a square instead: the Great Square of Pegasus.
冬：參宿四、天狼星、南河三。春：大角星、角宿一、五帝座一。夏：織女星、牛郎星、天津四。秋天則是一個四邊形：飛馬座大四邊形。
Classroom Activity 1 · 課堂活動一
You need · 準備材料
Steps · 步驟
Teaching tip: afterward, switch the 3D model to Night side and play it at 20 days a second. It is the same walk, with the real stars.
教學提示：活動結束後，把 3D 模型切到「看夜側」，用「每秒 20 天」播放，就是同樣的一圈，只是換成真實的星空。
Classroom Activity 2 · 課堂活動二
You need · 準備材料
Steps · 步驟
Safety tip: stargaze with an adult, and never look straight at the Sun. On a cloudy night, the sky chart in the 3D model shows the same view.
安全提示：觀星要有大人陪同，絕對不要直視太陽。遇到陰天，3D 模型旁的星空圖一樣看得到同樣的景象。
