# Tag Info

No, it's not. The radiation field in the interior of the Sun is very close to a blackbody spectrum. If you look in any particular direction the brightness (power per unit area) you see is $\sigma T^4$, where $\sigma$ is Stefan's constant. Given that the interior temperature, that might be $10^7\ \mathrm K$, then the surface brightness is $5.7 \times 10^{20}... 19 There is very little mixing in the core of the Sun, where the stratification is fixed by radiative (rather than convective) heat transfer. The heavier helium does "fill the core", but takes about 12 billion years to do so, during which time, the concentration of helium gradually increases. During its main sequence lifetime, most of the energy generation ... 16 Coming from a different direction as @Rob's, Opacity and Thermal Radiation are orthogonal properties of a material. The photon flux at the interior of the sun is very high, so it is definitely not dark. However, it is opaque to virtually all light outside the sun. To provide an analogy, if you are in a sealed room with no windows, you cannot see anything ... 12 If our sun was already in the process of becoming a red giant, would the gradual rise in luminosity be noticeable to our eyes at some point in human existence? I'd say no for a couple of reasons. @PM2Ring's comment: FWIW, in about 1.1 billion years it will be too hot for most lifeforms currently on Earth, long before the Sun starts moving off the main ... 7 Elaborating on the answer from James K, the azimuth of the sunrise depends on the declination of the Sun and the observer's latitude. The declination ranges between approximately +23.4 to -23.4 and depends on the date. $$\cos(\theta_R)=-\frac{\sin(declination)}{\cos(latitude)}$$ where$\theta_R$is the angle measured around the horizon from due south to ... 5 All points on the celestial sphere execute a full circle every (sidereal) day, but the speed of a point with nonzero declination is slower than a point on the celestial equator because it's traveling on a small circle, not a great circle. This is exactly the same as how a point on the terrestrial equator travels at a higher speed than a point not on the ... 3 It varies from place to place and from day to day, with a more extreme range of angles if you go further away from the equator. Calculating the angle (called the azimuth of the sun at sunrise) is possible, but not trivial. Instead you can get a computer to calculate it for you. The pyephem package or astropy can do this, if you use python. On the other ... 3 Closer than about 10000AU, 1.5 trillion km or about 2000 times the orbital radius of Jupiter. Three body systems are peculiar beasts, and but I'm going to change the question to "Would Jupiter be in a stable solar orbit?" This makes it a question of Hall radius. The Hall radius is$r_H = a\sqrt[3]{m/3M}$where$m/M=1/4000000\$ is the ratio of solar mass to ...