luminosity - How to convert contrast ratio to number of stops?

I have read an article from the below link about the human eye sensitivity and came to know that its dynamic contrast range is 1000000:1 or in other words 30 stops. They also mentioned static contrast ratio of 1000:1 is same as 10 stops. I believe if we have a million lights with light intensity from 1 to million, our human eye may able to see only 30 shades in that. I want to know how to relate the intensity to stops. Please give more clarification if i seems to be sounding like dumbo. Thanks. more

luminosity - Are lumens linearly additive?

If I have two light sources side by side emitting $1000~\rm lumens$ each, am I going to have the same amount of light emitted in an enclosed space (e.g. a room) as if I had a single light source that's emitting $2000~\rm lumens$?To ask a slightly different way: would $1000~{\rm lm} + 1000~\rm lm$ vs $2000~\rm lm$ be distinguishable to a small or large extent by looking at or measuring the brightness of a surface of the room?Or yet another way: is the relationship between the two lights a linear function or some non-linear one?...Read more

luminosity - What is the radiant intensity of the celestial sphere?

Specifically, excluding the Sun and the Moon:How much energy, as light and other frequencies reaches a point in space on the average, if you add up all the sources like distant stars, the Milky Way, distant galaxies, nebulae etc.? How much brighter is the space than "perfect blackness" on the average?Say, we've developed a magical solar battery that has 100% efficiency, can absorb all electromagnetic frequencies, is spherical, fully omnidirectional and has $1 m^2$ of cross-section surface (56cm radius); we sent it out halfway to Proxima Centau...Read more

luminosity - Question about radiation pressure

A spaceship with mass $m = 25\:kg$ is moving toward a red giant with $M = M_{sun}$ and $L = 1000\:L_{sun}$ (L: Luminosity). It is moving on a line (so this is not an orbital question). When it gets too close to the red giant, it's sensor open its solar sails (they get and then reflect the light completely), hence the radiation pressure help it to escape from the red giant (on the same line). Find the area of solar sail. (It is from National Olympiad of an Asian Country)My problem is with the radiation pressure formula. for solving this problem,...Read more

Converting the log (Stellar Luminosity/Solar Luminosity) and the log of the plus and minus variation

There are some stars in the NASA Exoplanet Archive that I am interested in but I am confused by the physical meaning of the terms.For example, there's a star BD+15 2940 with a log10 of Solar Luminosity of 2.01 +/-0.75 where the variation is also a log.So is the linear equivalents 18.2 to 575.44 with most likely value 102.33?I went to the citing paper Nowak et al. 2013and they quote it as log L*/LSun 2.01 +/- 0.75 as per the NASA archive....Read more

instruments - How to calculate luminosity in g-band from absolute AB magnitude and luminosity distance?

How can I calculate the (non-bolometric) luminosity $L$ of a galaxy (or a star for that matter) over a given band from its AB apparent magnitude $m_{AB}$ over that band and its luminosity distance $d_L$?For instance, consider the g-band which typically has a $\lambda_{eff} = 467 \text{ nm}$ and a $\Delta \lambda = 100 \text{ nm}$. Given this galaxy has an apparent AB magnitude of $m_g = 22.5$ and luminosity distance of $1991 \text{ Mpc}$ (i.e. $z = 0.355$ if you are curious), what is its luminosity? I know I shold use the following equation, bu...Read more

Solar luminosity proportional to $G^7$?

A book I recently purchased describes Dirac's proposed variation of Newton's G, and why that specific proposal wouldn't work because the earth would have been too hot for the known history of life. A footnote explains that the luminosity of the sun is proportional to the seventh power of G, which seems incredible to me. I know that this has to be a simplification, since stellar dynamics are annoyingly complex, but if we put that aside, is this essentially correct, or is it a typo? What would be the theoretical justification for this in broad te...Read more