Lecture 3 - Coordinate Systems Flashcards
*How is the local astronomical system defined?
Z-axis: negative gravity vector
X-axis: astronomical north
Y-axis: completes left handed system.
Origin: at the site of an observer on the surface of Earth - a topocentric system.
Measurements; altitude, azimuth
*What are the complications when it comes to True Right Ascension System?
The coordinate system changes with time, so do the coordinates of stars, thus ‘true’. This means we need to specify the epoch to which the coordinates refer.
*What is the Instantaneous Terrestrial System?
Z-axis: true spin axis
X-axis: line of intersection between instantaneous Greenwich Meridian and equatorial plane
Y-axis: completes RH system
Origin: topocentric
Measurements: astronomical latitude, astronomical longitude
Complications; x-axis moves with time
*What is the Apparent Place System?
The apparent place of an object is the position in space as seen by the observer.
Z-axis; true spin axis
X-axis: points towards Y
Y-axis: completes RH system
Origin: Center of mass of the Earth
*What is the Conventional Terrestrial System?
Z-axis: points to Conventional International Origin (CIO)
CIO: mean position of north pole determined by convention by the averaged pole positions from measurements from early 1900’s
Y-axis: completes RH system
Origin: Center of mass of the Earth
*What is the Mean Right Ascension System?
Z-axis: points to North Celestial Pole (NCP)
X-axis: points towards vernal point (Y)
Y-axis: completes RH system
Origin: Center of mass of the Sun
*What is parallax?
A displacement or difference in the apparent position of an object viewed along two different lines of sight.
*What is aberration?
Apparent motion of celestial objects about their locations dependent on the velocity of the observer.
*What is refraction?
Think light. The speed of light changes as it passes through a medium.
*True Right Ascension System
Z-axis: directed toward NCP
X-axis: points toward vernal point (gamma)
Y-axis: completes RH system
Origin: sun
Measurements: declination of star, right ascension.
What is annual parallax?
The distance that separates a star which is measured at two points. Annual parallax between Earth and Sun as parallactic angle of radius of Earth’s orbit subtended at star - the difference in apparent position of nearby star as viewed from the Sun and Earth.
What is diurnal (daily) parallax?
Parallax that varies with rotation of the Earth (or with difference of location on the Earth)
What is annual aberration?
Aberration resulting from Earth’s motion around the Sun.
What is diurnal aberration?
Aberration resulting from Earth’s spin about its axis.
*What is the Ecliptic System?
Z-axis: Earth’s precession axis
X-axis: points towards vernal point, Y
Y-axis: completes RH system
Origin: Center of mass of the Sun
Coordinates: ecliptic latitude, ecliptic longitude
