5239364
Description
Flashcards by Wilhelm André, updated more than 1 year ago
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Created by Wilhelm André
over 8 years ago
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| Question | Answer |
| Parsec | 3.09 x 10^16 m or 3.26 ly The distance at which one arcsecond is subtended by 1 astronomical unit. |
| Astronomical Unit | 1.496x10^11 m The average distance from Earth to the Sun. |
| Arcminutes & arcseconds | Arcminute: 1/60th of a degree Arcsecond: 1/60th of a arcminute Note: These are not "time-units" but really small degrees! |
| Speed of Light | 3.00x10^8 m/s The universal "speed limit". We use the symbol c for the speed of light. |
| Apparent magnitude | A measure of the brightness of a celestial object as seen from earth. Examples: Vega = 0, Sun = -27, |
| Brightness of Star | Energy flux received from a star. [b] = W/m^2 |
| Visible spectrum | Ranges from: 700nm (red) to 400nm (violet) |
| Electromagnetic spectrum | Radio: > 1mm Infrared: 1 mm - 700 nm Visible: 700 - 400 nm Ultraviolet: 400 - 10 nm X-ray: 10 - 0.1 nm Gamma-ray: < 0.1 nm |
| What is this equation equal to? | The frequency v, of an electromagnetic wave traveling at the speed of light c, with a wavelength lambda. [v] = Hz = s^-1 |
| Wien's Displacement Law | The wavelength lambda is were the intensity of a blackbody peaks at a given temperature T. |
| Stefan-Boltzmann Law | j is total energy per unit time, per unit surface given off by a blackbody. [j] = W/m^2 |
| Stefan Boltzmann Constant | 5.670 x 10^-8 W m^-2 K^-4 |
| Luminosity of a star | Stefan-Boltzmann Law give us the total energy per unit time, per unit surface. So to get the total energy per unit time (luminosity) we multiply by the area of the star. |
| Blackbodies | An object which absorbs all radiation that strikes it. Essentially a hole is a blackbody. Stars are also blackbodies. |
| Planck's Law (In terms of frequency) | Intensity of a blackbody. h is Planck's constant, v is frequency, k is Boltzmann's constant (Not Stefan-Boltzmann constant). |
| Planck's Law (In terms of wavelength) | Intensity of a blackbody. h is Planck's constant, v is frequency, k is Boltzmann's constant (Not Stefan-Boltzmann constant). |
| Planck's Constant | 6.626 x 10^-34 Js |
| Boltzmann Constant | 1.381 x 10-23 J/K |
| Received Energy Flux | This is the energy flux received from a star with luminosity L at a distance d. |
| How do you calculate stellar distances? | You want to find the distance d. 1. Note the position of the star relative to the stars behind it. 2. Wait 6 months and measure the shift in angle. 3. Divide this by 2 and you got your parallax angle theta. 4. Use the tangent formula to calculate d. Hint: Use tan(theta) ~= theta(radians) because the angle is so small. |
| Absolute Magnitude | The absolute magnitude M can be found if you know the distance d (in parsec) and the apparent magnitude m. This is the same as apparent magnitude but for a standard distance at 10pc. |
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