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Lecture 3

ASTA01H3 Lecture Notes - Lecture 3: Thuban, Gyroscope, Axial Tilt

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Kristen Menou

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Moe tha  eas ago, astooe Hippahus opaed a fe of his sta
positios ith those ade  othe astooes eal to etuies efoe hi.
He ealized that the elestial poles ad euato ee slol oig elatie to the
Late astooes udestood that this appaet otio is aused  a speial
otio of Eath alled peessio 歲差.
If ou hae ee plaed ith a to top o gosope 陀螺儀, ou a eall that the
ais of suh a apidl spiig ojet seeps aoud elatiel slol i a ile.
The eight of the top teds to ake it tip 傾倒.
This oies ith its apid otatio 自轉 to ake its ais seep aoud slol i
peessio otio.
Eath spis like a giat top, ut it does ot spi upight 直立 elatie to its oit
aoud the “u.
You a sa eithe that Eaths ais is tipped .°fo etial 垂直 o that Eaths
euato 赤道 is tipped .° elatie to its oit.
oliuit 傾角.
Eaths lage ass ad apid otatio keep its ais of otatio poited toad a spot
ea Polais 北極星alpha Usa Miois小熊󱕐.
Its ais dietio ould ot oe if Eath ee a pefet sphee.
Hoee, Eath has a slight ulge aoud its euato.
The gait of the “u ad Moo pull o this ulge, tedig to tist Eath’s ais
upight elatie to its oit.軌道
The oiatio 組合 of these foes ad Eath’s otatio auses Eath’s ais to
peess i a slo iula seep – takig aout   eas fo oe le.
As the elestial poles ad euato ae defied  Eaths otatioal ais, peessio
oes these efeee aks.
Egptia eods sho that  eas ago the oth elestial pole as ea Thua
alpha Daois天龍󱕐a pale ello sta.
 No, the pole 極點 is appoahig Polais ad ill e losest to it i aout .
I aout , eas, the elestial pole 天極 ill hae oed to the appaet
iiit 附近 of the e ight sta Vega alpha Lae.
otatio is the tuig of a od o its ais. 自轉
Eath otates o its ais – ad that podues da
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