# Tag Info

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I generally regard NASA as authoritative, and they report the orbital parameters on their Earth Fact Sheet. I note that they disagree with Wikipedia about the aphelion though they agree on the perhelion, semi-major axis and eccentricity: NASA Wikipedia Aphelion 152.10 151.93 Perhelion 147.09 147.095 Semi-major 149.60 ...

19

Are there any exact data about Earth's orbit? No. There are always measurement errors. There are however very good estimates. The best estimates come from three competing organizations, the Jet Propulsion Laboratory (the Development Ephemeris models), the Russian Institute for Applied Astronomy (the Ephemerides of the Planets and Moon), and the IMCCE ...

5

Tyco Brahe Observed Mars. And as the Mars is out side us, and rotates slower, it has an particular character that it even moves to "wrong direction" in the sky for a while. It must have been partially luck, that 5 of these observations is measures with enough accuracy this important point in orbit. (see link) Or maybe this was exactly the interesting ...

4

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 ...

3

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 ...

2

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 ...

2

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, ...

2

They couldn't carry sufficently accurate time from London with portable clocks. But they were able to use clocks to time measure the time between the sun crossing and the transit of stars the night before and after. The absolute transit time of stars can be trivially obtained if you know the site's longitude. If you are on land and have an observatory ...

2

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 ...

2

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 ...

2

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 ...

2

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 ...

2

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 ...

1

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.

1

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 ...

1

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 ...

1

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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