         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 - Magnitudes A Magnitude is the measure of brightness of a celestial object. It is a logarithm scale that is used to determine levels of brightness between other stars. The ratio of apparent brightness between two stars is: There are actually two types of Magnitude: apparent and absolute. Apparent magnitude is the how bright a star looks from Earth. Absolute magnitude is the true brightness of a star. When comparing the apparent and absolute magnitude of a star, we get what is called the Distance Modulus: This is actually a very powerful equation in that if we know the absolute and apparent magnitude of a star, we can determine its distance - and its pretty accurate too. In addition to comparing stars, we can also compare color ratios between stars to learn surface temperature. This color ratio is also called a B-V ratio (B=blue, V=visual or green) that is determined by using filters (Blue and Green in this case): For example, a star with a V < B ratio, the surface temperature is higher than a star with a V > B ratio. As a note, other filters can be (and often are) used. 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.