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Neptune, which is Uranus's near twin in size and composition, radiates 2.61 times as much energy into space as it receives from the Sun, [23] but Uranus radiates hardly any excess heat at all. The total power radiated by Uranus in the far infrared (i.e. heat) part of the spectrum is 1.06 ± 0.08 times the solar energy absorbed in its atmosphere .
To help compare different orders of magnitude, this section lists lengths between 10 −3 m and 10 −2 m (1 mm and 1 cm). 1.0 mm – 1/1,000 of a meter; 1.0 mm – 0.03937 inches or 5/127 (exactly) 1.0 mm – side of a square of area 1 mm²; 1.0 mm – diameter of a pinhead; 1.5 mm – average length of a flea [27]
Distance of the outer limit of Oort cloud from the Sun (estimated, corresponds to 1.2 light-years) — Parsec: 206 265 — One parsec. The parsec is defined in terms of the astronomical unit, is used to measure distances beyond the scope of the Solar System and is about 3.26 light-years: 1 pc = 1 au/tan(1″) [6] [61] Proxima Centauri: 268 000 ...
The choice of solar mass, M ☉, as the basic unit for planetary mass comes directly from the calculations used to determine planetary mass.In the most precise case, that of the Earth itself, the mass is known in terms of solar masses to twelve significant figures: the same mass, in terms of kilograms or other Earth-based units, is only known to five significant figures, which is less than a ...
The moons of the trans-Neptunian objects (other than Charon) have not been included, because they appear to follow the normal situation for TNOs rather than the moons of Saturn and Uranus, and become solid at a larger size (900–1000 km diameter, rather than 400 km as for the moons of Saturn and Uranus).
For the giant planets, the "radius" is defined as the distance from the center at which the atmosphere reaches 1 bar of atmospheric pressure. [11] Because Sedna and 2002 MS 4 have no known moons, directly determining their mass is impossible without sending a probe (estimated to be from 1.7x10 21 to 6.1×10 21 kg for Sedna [12]).
List of orders of magnitude for areas 10 −8 to 10 −1 square metres; Factor (m 2) Multiple Value Item 10 −8 55,000 μm 2: Size of a pixel on a typical modern computer display: 10 −7 2-400,000 μm 2: Cross-sectional area of a mechanical pencil lead (0.5-0.7 mm in diameter) [16] 10 −6: 1 square millimetre (mm 2) 1–2 mm 2: Area of a ...
For this reason, scientists often classify Uranus and Neptune as "ice giants" to distinguish them from the gas giants. Uranus's atmosphere is similar to Jupiter's and Saturn's in its primary composition of hydrogen and helium , but it contains more " ices " such as water, ammonia , and methane , along with traces of other hydrocarbons .