Positional Astronomy
Spherical astronomy, or positional astronomy, is a branch of observational astronomy used to locate astronomical objects on the celestial sphere, as seen at a particular date, time, and location on Earth. It relies on the mathematical methods of spherical trigonometry and the measurements of astrometry. This is the oldest branch of astronomy and dates back to antiquity. Observations of celestial objects have been, and continue to be, important for timekeeping and navigation. The science of actually measuring positions of celestial objects in the sky is known as astrometry.
The unaided human eye can perceive about 6,000 stars, of which about half are below the horizon at any one time. On modern star charts, the celestial sphere is divided into 88 constellations. Every star lies within a constellation. Constellations are useful for navigation. Polaris lies nearly due north to an observer in the Northern Hemisphere. This pole star is always at a position nearly directly above the North Pole.
In this unit, we will cover:
- The celestial sphere and its coordinate systems
- Timekeeping
- Perturbations in the measurement of celestial positions
- Sun’s motion and its effects on seasons
- Moon’s phases and eclipses
- Planetary motion
Recommended Reading
- Chapter 1 and 2 of “Foundations of Astrophysics” by Barbara Ryden and Bradley M. Peterson
- Chapter 1 of “An Introduction to Modern Astrophysics” by Bradley W. Carroll and Dale A. Ostlie
- Chapter 1, 2, 3, 5 and 6 of “Fundamentals of Astronomy” by Flavio Salvati
- Chapter 2 of “Fundamental Astronomy” by Hannu Karttunen et al.
- Chapter 7, 8, 9, 10, 11 and 12 of “Astronomy: Principles and Practice” by A. E. Roy and D. Clarke