# Tag Info

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Earlier this year I had a chance to take a photo of the "blood moon" - the eclipse of September 27, 2015. I used an "ordinary" camera: a Panasonic FZ200 with 25x optical zoom, without a tripod but with image stabilization. When I looked at the pictures on a big screen, I noticed a few little dots in the background which I initially assumed to be noise (or ...

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The one closest to zero is the best fit, but depending on the conditions you can't rule out the model with 1.28. Most often you cannot rule out anything where Chi-squared is closer than 1 to the value of your best fit - but it does depend in reality on a bunch of things including the number of variables you used for your model fit, for example. Numerical ...

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My answer to How does the Hubble parameter change with the age of the universe? (which is itself adapted from Equation for Hubble Value as a function of time) explains how to calculate the scale factor. In fact we calculate the time as a function of the scale factor rather than the other way around. The equation we use is:  t(a) = \frac{1}{H_0}\int_0^a ...

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This question has been asked and answered (by me) on Astronomy Stack Exchange: It's brighter on Pluto than you think. NASA developed a tool called Pluto time, which tells you when at your place the ambient light conditions are similar to the ones on Pluto. This occurs when the Sun is only 2° below the horizon! That's quite shortly after sunset, ...

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I'd like to know what would happen if Venus was flung into a highly eccentric orbit like Sedna (except maybe with its current perihelion) with an orbital period measured in thousands of years. It's kind of a weird question but the first thing to consider is whether the orbit crosses any other planetary orbits, cause if it does, the biggest effect of ...

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To determine transit UTC transit time of a celestial object; (360 plus your Longitude) minus star SHA= GHA Aries Get GHA Aries from The Nautical Almanac here; www.TheNauticalAlmanac.com To determine transit time of the Sun on your meridian (Longitude); Sun GHA = your Longitude. Let's say you're located at W 078 degrees 42 minutes. Date- November 18, ...

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Speed of sound usually refers to the propagation velocity of a low amplitude vibration in a medium in equilibrium. A "sound" can travel far faster than the speed of sound if it is, for example, a shock wave

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it's likely that when you google the term in general, most pages treat about the "speed of sound" at the common human meaning (sound in air :-) ), while its generalization to all the various circumpstances of fluids in the universe might more often been spelt "sound speed". But here it's more linguistic than physics, and it wouldn't be physically incorrect ...

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I think it has to do with their relative intensities and the high density of food compared to the low density of the universe, This is correct. The microwave ovens are not working with a black body radiation curve with an average of 3K , nor is the heating effect a thermal balance between two black bodies: food and microwave. Bodies in space away from ...

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The reason that there is a CMB is because of the big bang. The photons from the very beginning of our universe has spread (almost)uniformly throughout the universe to give rise to a general noise which we call background. Now to answer your question, as the universe expanded after big bang the photons got redshifted and their energy decreased. Now the avg ...

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Although not a complete answer, one place to start is with the coldest naturally occurring place in the universe, which is the Boomerang Nebula, a planetary nebula that is around 1 K. As best as I can tell, this cooled below the CMB temperature simply by adiabatic expansion, and is insulated in its interior from CMB heating. Is this a feasible way to get to ...

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There is another big problem with ultra-small luminosities: due to the small initial light + 1/r² decrease, it might be that only a few photons per hour sent by your target planet reach the diameter of Earth (better be in your telescope ! ). At very small luminosity you have to remind that light is not continuous and made of photons. And way before the ...

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The spatial resolution of a telescope is going to be limited in what it can resolve by something called the diffraction limit. Basically, light can only be focused so much by a lens given its initial starting size and the focal length of the lens. Its useful to think about this in terms of angular resolution for the case of telescopes, and the minimum ...

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the answer is no: for now there is a high correlation between the properties of planets (size, distance to their star) and their probability to be detected, which totally bias the observed distribution.

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There are several broadband light sources in outer space such as quasars and blazars which basically can act as a light bulb. Earth bound telescopes as well as satellite telescopes can see absorption features in the light when the light passes through some cloud in outer space that contains molecules before the light reaches earth. In addition molecules in ...

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The elements you give describe an idealised orbit that does not exist in reality. Those numbers are parameters to an approximate model. Earth's closest distance to the sun is different each and every year, by a lot (about 20,000 km in fact). Are there any exact data about Earth's orbit? There are certainly far better models than the 6-parameter ...

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A Galaxy cluster could have $10^{14}$ solar masses within a radius of 5 Mpc. In this case $GM/Rc^2 \sim 10^{-6}$, equivalent to a velocity shift of less than 1 km/s. Our own Milky Way has a mass of around $10^{12}$ solar masses within 100 kpc. This gives a gravitational redshift of about 100 m/s. These are completely negligible compared to cosmological ...

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The gravitational red shift is only significant for black holes – where the coefficient may grow arbitrarily large in the vicinity of the horizon – and the neutron stars – where the frequency drops to something comparable to 50%. For all other celestial objects, the red shift is much smaller than one. And only planets and white dwarfs are objects for which ...

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