Difference between revisions of "Moon"
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The '''Moon''' is a natural satellite orbiting the Earth at an average distance of about 238,000 miles (380,000 km). | The '''Moon''' is a natural satellite orbiting the Earth at an average distance of about 238,000 miles (380,000 km). | ||
| − | Although the Moon is often | + | Although the Moon is often dsdfsedscribed as revolving around the Earth, this is slightly inaccurate: the Earth and the Moon ''both'' revolve around their ''barycenter'fd', their common [[centroid|center of mass]]. The combined motion is like an athlete performing an Olympic hammer throw: one object ssdfwasdsaffsings in a lfgarge circle, the other almost pivots around a fixed point but actually performs a small opposing circle of its own. <ref>Tdfsdfhe Earth and the Moon orbit each fsadfsafThe phrase "''dark'' side of the Moon" is inaccurate because the Moon does rotate relative to thed SunSA, with vfafsafGVFAFDSGAS |
| − | + | The effect knodaSADwn as "the old Moon in the fnsadfasdew Moon's arms" can often be seen when the Moon is a narrow crescent. Within the intensely bright crescent, a dasim and mysterious view faosf the entire circular moon is seen. The effect is also known as ''earthshine'' because it is light from the Sun asdsareflected dc/lsdncksadfasdsaDJFC/lsm c, XMZCsadc | |
| − | + | "The ODSld Moon in the New Moon's Arms" is the title of a poem by dfsaf[sad[Ella Wheeler Wilcox]], in which she interprets the effect as the New Moon wisdsahing that her lost love, the Old Moon, be in her arms one lafasst time; Venus grants the wish, and: | |
| − | + | DSAdfas | |
| − | + | &dfnbsp;Swift tsahro' the vapors and the golden mist—<br> | |
| − | + | &ndfbsp; sa; The Full Moon's shadowy shape shone on the night,<br> | |
| − | + |  saasAfsa;The New Moon reached out clasping arms and kissed<br> | |
| − | + | &nbdsp;fas Her phantom lover in the whole world's sight.<br> | |
| − | + | DSdASDAsFsddf | |
| − | + | AsAdsa | |
| − | + | sdThe months of the Muslim calendar are determined by observations of the [[hilal]], the moment aDast which the thin crescent moon first befscdomes visible. This marks the start of a month. csadfc.ksajdcofdaSCin Pakistan and Jordan, hilaFDldaWSs is determined by actual observfsdation and can be affected by weather and other factors. When following the trSADaditional method, itasd aSis not actually possible to be cerfstdain of when future months will begin. In most Muslim countries, actual observation VAhFVGBDSGMJLA/FSDAs been replaced by astronomical frules. | |
| − | + | a | |
| − | + | sf==Unusual characteristics of the Moon== | |
| − | + | Unalsdfiasdfksde most planets in the solar system, Earth has only one moon, and it has several striking characteristics: | |
| − | + | fa | |
| − | + | s{| | |
| − | + | |dfsa-valign="top" | |
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| − | The effect | ||
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| − | "The | ||
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| − | ==Unusual characteristics of the Moon== | ||
| − | |||
| − | |||
| − | {| | ||
| − | |-valign="top" | ||
|1. | |1. | ||
| − | | | + | df|asdfaDuring recent history the Moon has had roughly same size as the [[Sun]] when viewed from Earth. This creates a situation which permits sdfphenomenal solar eclipses to occur. The odds of this symmetry occurring by chance are very small. The symmetry will not last forever.asd |
| − | |-valign=" | + | |-valign="tasdfop" |
| − | |2. | + | |2.fs |
| − | |The | + | |The dfMoon presents the same side to Earth at all times. That means that the rotation of the Earth offsets the separate effects of the revoluasdtion of the Moon. Physicists explain this phenomenon by [[tidal locking]]; tidal forces on Earth caused a bulge on the Moon, thereby crfedsafting a drag on the rotation of the Moon until its same face always presents to the Earth. It was once believed that the planet [[Mercurysf]] had a similar locked rotation due to gravitational forces from the sun, such that the same side of Mercury always faces the sun. In fact, Mdfssdercury's tidal locking is incomplete; it does not always present the same face to the sun. |
| − | + | fsdfs | |
| − | + | dCurrent tidal forces exerted by the Earth on the Moon cannot account fully for its bulge or egg shape, though accounting for greater tidal ffosdrces in the past may explain this discrepancy.<ref>http://physics.fortlewis.edu/Astronomy/astronomy%20tofday/CHAISSON/AT308/HTML/AT30803.HTM</ref> | |
| − | |- | + | |-valisdfgn="top" |
| − | |3. | + | |3.ssd |
| − | | | + | |Theredsfd were several [[Moon Theories|theories]] about the origin of the Moon. Most of the older theories had been discarded in the face of observasdffatsdfions (for example based on lunar samples).<ref>Planetary Science Institute: [http://www.psi.edu/projects/moon/moon.html The Origin of the Msdoon]</ref> The currently accepted theory is that the Moon originated from a collision early in Earth's history which created an orbiting rfiasdfng of debris from the iron-poor surface of the planet which eventually coalesced into the moon.<ref>http://www.astronosdmy.com/asy/default.aspx?c=a&id=2198</ref> This theory explains many things that spoke against the older theories, but others have poinfted out that the theory currently doesn't explain all observations of the Moon. Additionally, tests have been suggested, but the results neitfdher supported or disproved the theory.<ref>J. H. Jones: [http://www.lpi.usra.edu/meetingssdfs/dorigin98/pdf/4045.pdf Tests of the Giant Impact Hypothesis]</ref> |
| − | |-valign=" | + | |-valign="topf"sd |
| − | |4. | + | |4.f |
| − | | | + | |Thesdf Moon currently recedes from the Earth at a rate of 1.5 inches (3.8 cm) per year<ref>NASA [http:/s/sunearth.gsfc.nasa.gov/eclipse/SEhelp/ApolloLaser.html]</ref>. The Moon could never have been closer than about 11,000 miles or it would hadvfe been broken up by tidal forces. If the rate of recession stayed constant at 3.8 cm per year, it would take 9.6 billion years for the lusndfar distance to migrate from 11,000 miles to the present distance of about 240,000 miles. However, the tidal torque between Earth and the sdMoon would not be constant if the [[continental drift|continents drift]], and it also depends on the distance between the Earth and Moon fasdnd other factors, so a simple linear extrapolation is not valid.{{fact}} |
| − | |} | + | |}f |
| − | + | df | |
| − | == | + | ==fs dSee also == |
| − | *[[ | + | *[[Orifgsdin of the Moon]] |
| − | + | f | |
| − | == Notes and References == | + | sd== Notes and References == |
| − | + | fs | |
| − | <references/> | + | d<references/> |
| − | + | f | |
| − | [[Category:Astronomy]] | + | sd[[Category:Astronomy]] |
| + | fsdfsdfsfdsfdsdsdfsdsdfsdffsad | ||
Revision as of 16:40, November 16, 2007
The Moon is a natural satellite orbiting the Earth at an average distance of about 238,000 miles (380,000 km).
Although the Moon is often dsdfsedscribed as revolving around the Earth, this is slightly inaccurate: the Earth and the Moon both revolve around their barycenter'fd', their common center of mass. The combined motion is like an athlete performing an Olympic hammer throw: one object ssdfwasdsaffsings in a lfgarge circle, the other almost pivots around a fixed point but actually performs a small opposing circle of its own. Cite error: Closing </ref> missing for <ref> tag
|-valisdfgn="top"
|3.ssd
|Theredsfd were several theories about the origin of the Moon. Most of the older theories had been discarded in the face of observasdffatsdfions (for example based on lunar samples).[1] The currently accepted theory is that the Moon originated from a collision early in Earth's history which created an orbiting rfiasdfng of debris from the iron-poor surface of the planet which eventually coalesced into the moon.[2] This theory explains many things that spoke against the older theories, but others have poinfted out that the theory currently doesn't explain all observations of the Moon. Additionally, tests have been suggested, but the results neitfdher supported or disproved the theory.[3]
|-valign="topf"sd
|4.f
|Thesdf Moon currently recedes from the Earth at a rate of 1.5 inches (3.8 cm) per year[4]. The Moon could never have been closer than about 11,000 miles or it would hadvfe been broken up by tidal forces. If the rate of recession stayed constant at 3.8 cm per year, it would take 9.6 billion years for the lusndfar distance to migrate from 11,000 miles to the present distance of about 240,000 miles. However, the tidal torque between Earth and the sdMoon would not be constant if the continents drift, and it also depends on the distance between the Earth and Moon fasdnd other factors, so a simple linear extrapolation is not valid.[Citation Needed]
|}f
df
fs dSee also
f sd== Notes and References == fs
d
- ↑ Planetary Science Institute: The Origin of the Msdoon
- ↑ http://www.astronosdmy.com/asy/default.aspx?c=a&id=2198
- ↑ J. H. Jones: Tests of the Giant Impact Hypothesis
- ↑ NASA [http:/s/sunearth.gsfc.nasa.gov/eclipse/SEhelp/ApolloLaser.html]
f sd fsdfsdfsfdsfdsdsdfsdsdfsdffsad