         Introduction Astronomy Tools Concepts 1. Electromagnetic Spectrum 2. Atmosphere Limitations 3. Space Observations Equipment 1. Telescopes 2. Radio 3. Space Tools 4. Photography 5. Spectroscopy 6. Computers 7. Advanced Methods 8. Radio Astronomy Basic Mathematics Algebra Statistics Geometry Scientific Notation Log Scales Calculus Physics Concepts - Basic Units of Measure - Mass & Density - Temperature - Velocity & Acceleration - Force, Pressure & Energy - Atoms - Quantum Physics - Nature of Light Formulas - Brightness - Cepheid Rulers - Distance - Doppler Shift - Frequency & Wavelength - Hubble's Law - Inverse Square Law - Kinetic Energy - Luminosity - Magnitudes - Convert Mass to Energy - Kepler & Newton - Orbits - Parallax - Planck's Law - Relativistic Redshift - Relativity - Schwarzschild Radius - Synodic & Sidereal Periods - Sidereal Time - Small Angle Formula - Stellar Properties - Stephan-Boltzmann Law - Telescope Related - Temperature - Tidal Forces - Wien's Law Constants Computer Models Additional Resources 1. Advanced Topics 2. Guest Contributions Physics - Formulas - Small Angle Formula Some objects in the sky have an apparent size - like the moon. By understanding geometry and the nature of circles, it is possible to determine the distance to the object, or the physical diameter of the object.With regard to measure, the standard in Astronomy is degrees and arcseconds. Here is the conversion factors: As an example of this equation in use, I will use the example shown in the reference text: To determine the physical diameter of Jupiter (on July 26, 2003), we can use what is called the small angle formula: D = linear (physical) diameter α =  angular size in arcseconds = known for Jupiter 31.2 arcseconds d = distance to object = known for Jupiter = 943,000,000 km 206,265 = is required (arcseconds per radian) This is in good agreement with the actual diameter of Jupiter (142,984km). Back to Top      Search | Site Map | Appendix ©2004 - 2020 Astronomy Online. All rights reserved. Contact Us. Legal. The works within is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.