Introduction to Astrophysics
Instructor-
Golam Dastegir Al-Quaderi
Professor
Department of Physics, DU
1
, Observing Celestial Bodies
• Observation of celestial bodies include measuring the
following useful properties:
• A. Position of the celestial bodies in the sky which
include:
• i. Angular position of the bodies in the celestial sphere.
• ii. Distance from the Earth of the bodies.
• B. Luminosities of light of various wavelengths coming
from the bodies.
• C. Velocities at which the bodies are receding or
approaching the Earth, or in the tranverse direction.
2
, Observing Celestial Bodies
• Among these, we had previously learned about
specifying the angular position of the bodies on
the celestial sphere.
• The angular positions were represented by the
coordinates of right ascension 𝛼 and declination
𝛿 in the Celestial or Equatorial Coordinate
System.
• The distance measurement involves adopting
different methods for celestial bodies situated at
different distance scales.
3
, Observing Celestial Bodies
• The Distance Ladder: Astronomical bodies lying at
different distance scales require adopting
different distance measurement techniques.
• The ranges in which these techniques apply
overlap and one method is used to calibrate the
next method.
• Hence, calibration of one technique depends on
the calibration of the previous technique, lower
in the hierarchy of the techniques or ranges.
4
Instructor-
Golam Dastegir Al-Quaderi
Professor
Department of Physics, DU
1
, Observing Celestial Bodies
• Observation of celestial bodies include measuring the
following useful properties:
• A. Position of the celestial bodies in the sky which
include:
• i. Angular position of the bodies in the celestial sphere.
• ii. Distance from the Earth of the bodies.
• B. Luminosities of light of various wavelengths coming
from the bodies.
• C. Velocities at which the bodies are receding or
approaching the Earth, or in the tranverse direction.
2
, Observing Celestial Bodies
• Among these, we had previously learned about
specifying the angular position of the bodies on
the celestial sphere.
• The angular positions were represented by the
coordinates of right ascension 𝛼 and declination
𝛿 in the Celestial or Equatorial Coordinate
System.
• The distance measurement involves adopting
different methods for celestial bodies situated at
different distance scales.
3
, Observing Celestial Bodies
• The Distance Ladder: Astronomical bodies lying at
different distance scales require adopting
different distance measurement techniques.
• The ranges in which these techniques apply
overlap and one method is used to calibrate the
next method.
• Hence, calibration of one technique depends on
the calibration of the previous technique, lower
in the hierarchy of the techniques or ranges.
4
