train:lectures:positionalastro

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train:lectures:positionalastro [2024/03/18 12:57] – Roy Proutytrain:lectures:positionalastro [2024/03/18 16:10] (current) – Roy Prouty
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-The March Equinox is chosen to be the zero-point for the Equatorial Coordinate analogous to latitude -- the Right Ascension or RA. RA is measured eastward along the Celestial Equator starting at the March Equinox.+The March Equinox is chosen to be the zero-point for the Equatorial Coordinate analogous to latitude -- the Right Ascension or RA. RA($\alpha$) is measured eastward along the Celestial Equator starting at the March Equinox.
 ==Milankovitch Cycles== ==Milankovitch Cycles==
 The specific location of the CNP/CSP/CEq do change over time in cycles known as {{https://en.wikipedia.org/wiki/Milankovitch_cycles|Milankovitch Cycles}}. These cycles are symptomatic of the Precession/Nutation of the Earth's rotation axes, Orbital Eccentricity, and Orbital Obliquity. They're due to the gravitational effects of the masses in our Solar System being more in-line with the Ecliptic than our Celestial Equator! How fun!?   The specific location of the CNP/CSP/CEq do change over time in cycles known as {{https://en.wikipedia.org/wiki/Milankovitch_cycles|Milankovitch Cycles}}. These cycles are symptomatic of the Precession/Nutation of the Earth's rotation axes, Orbital Eccentricity, and Orbital Obliquity. They're due to the gravitational effects of the masses in our Solar System being more in-line with the Ecliptic than our Celestial Equator! How fun!?  
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-Declination is measured in degrees, minutes of arc and seconds of arc with $360^\circ$ if traversing any Great Circle containing the CNP and CSP. Right Ascension is measured in hours, minutes, and seconds with $24^h$ if traversing the full Celestial Equator. As we shall see, changes in RA correspond to different angular rotations of the Earth -- or different times of day! These units can be confusing. Minutes of arc (or arcminutes) are NOT the same as minutes of RA. Furthermore, the notation of RA & DEC can be confusing. They can be given in their fully qualified notation $(D_1^\circ~D_2'~D_3'', R_1^h, R_2^m, R_3^s)$, as degree-decimals, or some fun mixture of the two! When looking at a very small Field of View, angular measures in RA will frequently just be in terms of arcminutes or arcseconds. Pay careful attention to these notations and values. Be sure you understand the differences between them!+Declination is measured in degrees, minutes of arc and seconds of arc with $360^\circ$ if traversing any Great Circle containing the CNP and CSP. Right Ascension is measured in hours, minutes, and seconds with $24^h$ if traversing the full Celestial Equator. As we shall see, changes in $\alpha$ correspond to different angular rotations of the Earth -- or different times of day! These units can be confusing. Minutes of arc (or arcminutes) are NOT the same as minutes of RA. Furthermore, the notation of $\alpha$ & $\delta$ (RA & DEC) can be confusing. They can be given in their fully qualified notation $(D_1^\circ~D_2'~D_3'', R_1^h, R_2^m, R_3^s)$, as degree-decimals, or some fun mixture of the two! When looking at a very small Field of View, angular measures in $\alpha$ will frequently just be in terms of arcminutes or arcseconds. Pay careful attention to these notations and values. Be sure you understand the differences between them!
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   - the CSP will never be above the local horizon (Why?)   - the CSP will never be above the local horizon (Why?)
   - the CEq will intersect the local meridian at $(ALT=90^\circ - \lambda, AZ=180^\circ)$   - the CEq will intersect the local meridian at $(ALT=90^\circ - \lambda, AZ=180^\circ)$
-  - Zenith will see changing RA, depending on the local time, but the DEC will always be $\lambda^\circ$+  - Zenith will see changing RA, depending on the local time, but the $\delta$ will always be $\lambda^\circ$
  
-=====Stellarium=====+=====Stellarium Exercises=====
 Using Stellarium, let’s all do the following together … Using Stellarium, let’s all do the following together …
  
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           - Look up current Sidereal Time: https://www.localsiderealtime.com/            - Look up current Sidereal Time: https://www.localsiderealtime.com/ 
  
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 +Written by Roy Prouty 20240318\\
 +Reviewed by