Transcript Total Solar Eclipse

Astronomy 4230
天文学概论
A Brief Course of Astronomy
张景波
哈尔滨工业大学物理系
哈尔滨市天文爱好者协会
Location: L331
Tel: 86414104
30hours 3hours/times
Sunday, 1st-3rd Class
Room: A413
http://jinux.hit.edu.cn
E-mail:[email protected]
Lectrure 1 Sky and Cosmos
宇宙的尺度
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天球
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地平坐标系
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赤道坐标系
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低平高度与纬度的关系
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星座
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星座
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星座
星座
猎户座
和
大犬座
大熊座和北斗七星
太阳的运动
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太阳的表面特征
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黄道十二宫
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太阳与四季
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太阳日和恒星日
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月亮的运动
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日食和月食
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Eclipsis
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月食 Lunar Eclipses
• Umbra: Inner core of total darkness
– The disc of the Sun is completely blocked.
• Penumbra: Outer, partial shadow
– Sun's disc is only partly blocked, with a bit peeking over
the edge.
• Lunar Eclipses are when the Moon passes through the
shadow of the Earth.
• They only occur during Full Moon when the Earth is
between the Moon and the Sun.
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月食原理
Umbra
Penumbra
Sun
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Earth
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月食原理
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Lunar Eclipses
• Total Length of Earth’s Umbra
– ~1.4 Million km long
– About 3.7x the mean Earth-Moon distance.
• Umbra's width at the distance of the Moon
– 9000 km
– ~2.6x the Moon's diameter.
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Three Types of Lunar Eclipses
• Total Lunar Eclipse:
– Entire Moon is within the Earth's umbra.
– Can spend up to 1h 40m in the umbra
– Whole show can last ~6 hours
• Partial Lunar Eclipse:
– Only part of the Moon enters the umbra.
• Penumbral Eclipse:
– Moon misses the umbra completely, only passes through
the penumbral shadow.
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Three Types of Lunar Eclipses
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Total Lunar Eclipse
Partial Lunar Eclipse
(Note the ruddy scattered sunlight)
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日食 Solar Eclipses
• Solar Eclipses occur when the Earth passes through
the shadow of the Moon.
• They only occur during New Moon when the Moon is
between the Earth and the Sun.
• Totality ‘incredibly’ spectacular
• The Moon's umbra is only 380,000 km long:
– Just long enough for the tip to touch the Earth.
– But not large enough to cover the entire Earth.
– Solar Eclipses seen only where the shadow passes overhead.
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日食原理
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Types of Solar Eclipses
• Total Solar Eclipse:
– The observer is inside the Moon's umbra.
– The Moon completely covers the Sun.
• Partial Solar Eclipse:
– The observer is inside the Moon's penumbra.
– Only see part of the Sun covered by the Moon.
• Annular Eclipse:
– The Moon is at or near apogee, and so is too small to
cover the Sun
– The Moon's umbra does not touch the Earth, so
observers in the shadow path see the Sun as a ring
("annulus").
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Total Solar Eclipses
• Total Solar Eclipses are localized and short:
– The Moon's umbral shadow is at most 267 km
across on the Earth.
– Totality lasts at most about 7.5 minutes.
– Only observers in the umbra see a total solar
eclipse.
– Observers in the penumbra see a partial solar
eclipse.
– Everyone else sees nothing.
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Rare Events – Why ?
• Eclipses are rare :
– From a given location on the Earth you see
• a Total Lunar Eclipse every 3 years (or so).
• a Total Solar Eclipse every 360 years.
• Why not :
– Each full moon = lunar eclipse
– Each New Moon = solar eclipse ??
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Why Eclipses are rare
• Moon’s orbit not perfectly aligned with
Ecliptic :
– ~5° tilt from Ecliptic
– Where the moon's orbit crosses the Ecliptic defines
the "Line of Nodes"
– Only get eclipses when the line of nodes and the
Sun line up at Full or New Moon.
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The Eclipse Year
• Line of Nodes aligns with Sun every 346.6
days. ("Eclipse Year“)
• But, it must be a Full or New Moon when the
nodes line up to have an eclipse.
• This happens only very rarely.
• Check out Fred Espenak’s Eclipse page
• http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html
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日地月关系
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行星的运动
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水星 Mercury
金星 Venus
地球 Earth
火星 Mars
木星 Jupiter
土星 Saturn
天王星 Uranus
海王星 Neptune
冥王星
Pluto
行星的运动
• Mercury
Venus
Mars
Jupiter
Saturn
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• Star-like
Appearance
• close to
Ecliptic
• Two
separate
cases :
– always
close to
Sun (Venus,
Mercury)
– appearance
at any point
of time
during
night/day
(Mars,
Jupiter,
Saturn)
内行星 Inferior Planets
• Mercury, Venus, ‘inferior’ planets
• Inferior Conjunction:
– Planet is between the Earth and the Sun.
• Superior Conjunction:
– Planet on the other side of the Sun from
Earth.
• During both conjunctions, the inferior planet
appears to rise and set with the Sun.
• Maximum Eastern Elongation:
– Planet is furthest East of the Sun as seen
from the Earth (28º Mercury, 47º Venus)
– Rises & sets after the Sun ("evening star")
• Maximum Western Elongation:
– Planet is furthest West of the Sun as seen from the Earth.
– Rises & sets before the Sun ("morning star")
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金星的视运动
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外行星 Superior Planets
• Opposition:
– Planet is opposite the Sun in the sky.
– Rises as the Sun sets
– Highest in the sky at midnight.
• Conjunction:
– Planet is on the same side of the sky as the
Sun.
– Rises with the Sun
• Eastern Quadrature:
– Planet at right angles to the Earth-Sun line.
– Planet rises at noon, sets at midnight.
• Western Quadrature:
– Planet at right angles to the Earth-Sun line.
– Planet rises at midnight, sets at noon.
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火星的视运动
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行星的视运动
• In general, the planets move eastward relative to the "fixed"
stars.
– Called "Direct Motion".
– Motion is non-uniform (not at the same speed).
• Sometimes, however, the planets appear to
–
–
–
–
Slow down & stop!
Start moving westward, or RETROGRADE,
Slow down & stop again,
Resume moving eastward again.
• Apparent retrograde motion is observed in all planets.
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Summary
• Summary of Celestial Motions
– Fixed Stars:
• Uniform daily motion about the celestial poles.
– The Sun:
• Daily motion around the celestial poles (rising and setting).
• Eastward drift along the Ecliptic over a year, a little faster in winter,
slower in summer.
– The Moon:
• Daily motion around the celestial poles.
• Eastward motion near the Ecliptic over a month.
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Summary
• Summary of Celestial Motions
– The Planets:
• Daily motions about the celestial poles.
• Generally eastward motion near the Ecliptic at different
speeds for each planet.
• Occasional westward "retrograde" motions.
• Superior Planets are brighter at opposition, fainter at
conjunction.
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Homework
1.有一颗恒星1月1日在晚上10:00时升起，那
么它于下列日期将在什么时候升起？
(1) 1月4日
(2) 1月30日
(3) 7月1日
E-mail: [email protected]
before mar 12
Mar 5, 2006
Lecture 1, Astronomy 4230
J.B.Zhang