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Planet Discovery Mean Orbital Orbital Eccent- Inclination Radius or Diameter
/Astronom- Year Radius Period ricity to Ecliptic (R_eq_⊕ or D_eq_⊕)
ical Object (AU) (Jyr) (°)
Mercury prehistory 0.387098 0.240846 0.205630 7.005 0.38251
Venus prehistory 0.723332 0.615198 0.006772 3.39458 0.94884
Earth prehistory 1.000001018 1.000017... 0.0167086 0.00005 1
Earth UE Gr-Ro Ant. 1.0094 1.000017... ? 0.00005 0
Earth L2 c.1750 1.010 1.000017... ? 0.00005 0
Mars prehistory 1.523679 1.8808 0.0934 1.850 0.53248
Vesta 1807 2.36179 3.63 0.08874 7.14043 0.04489
Ceres 1801 2.7675 4.60 0.075823 10.593 0.07566
Jupiter prehistory 5.20260 11.8618 0.048498 1.303 11.209
Saturn prehistory 9.554909 29.4571 0.05555 2.485240 9.4492
Uranus 1781 19.2184 84.0205 0.046381 0.773 4.0073
Neptune 1846 30.110387 164.8 0.009456 1.767975 3.8826
Pluto 1930 39.54 248.00 0.24905 17.1405 0.1861
Eris 2005 67.781 558.04 0.44068 44.0445 0.1823
Planet Nine? 2025 est. 700 est. 1500 est. 0.6 est. 30 est. 3 est.
Notes:
- The quantities:
planet or
planet-like
astronomical object
and Earth's L2 point,
discovery
year,
mean orbital radius
(in astronomical units (1 AU= 1.49597870700*10**11 m)),
eccentricity,
orbital inclination
(in degrees),
equatorial
radius/diameter
(or whatever is largest specified radius/diameter;
in Earth equatorial radii
(R_eq_⊕ = 6378.1370 km)/Earth equatorial diameters
(D_eq_⊕ = 12756.2740 km)),
orbital period
(in Julian years (1 Jyr = 365.25 days)).
- The astronomical objects,
their astronomical symbols
(if there is one), and
discovery
years
(if there is one, otherwise prehistory)
in order of increasing
mean orbital radius:
Mercury ☿,
Venus ♀,
Earth ⊕,
Earth's Umbra Extent (UE)
(known since Greco-Roman antiquity),
Earth L2 point
(discovery circa 1750 by
Leonhard Euler (1707--1783):
see Wikipedia: Lagrange point: History),
Mars ♂,
asteroid
Vesta ⚶ (1807),
asteroid
Ceres ⚳
(1801),
Jupiter ♃,
Saturn ♄,
Uranus ⛢ or ♅
(1781),
Neptune ♆
(1846),
Kuiper Belt object (KB0)
ex-planet Pluto ♇
(1930),
scattered disk object (SDO)
Eris
(2005),
hypothetical
Planet Nine
(2025 estimated).
- For the data, see
and the linked names above.
The data are probably mostly
epoch J2000, but
yours truly has NOT checked this---there is a limit
to finickiness.
- It may see odd, that the Earth
mean orbital radius,
orbital period, and
orbital inclination values
are NOT exactly, respectively,
1,
1,
and 0.
But the fact is that
Solar System evolves in time:
slowly, but noticeably,
to modern
accuracy/precision.
The evolution is
due to astronomical perturbations
(mainly
gravitational perturbations)
caused by the mutual interactions of the
Solar System objects.
So invariant natural standards have been been defined to avoid the confusion of having
to update both astronomical values and the standards by which they are measured as time passes.
Determining evolving standards to high
accuracy/precision
is actually very difficult and finicky work.
We can explicate the cases of this note.
The modern
astronomical unit (AU) = 1.49597870700*10**11 m
exactly by definition.
The year used in astronomical work is
always the
Julian year = 365.25 days (exact by definition)
which differs slightly from the
sidereal year = 365.256363004 days (J2000)
(which is the
orbital period
relative to the observable universe).
The true ecliptic orientation
relative to the
invariable plane (of the Solar System)
(invariable relative to the
observable universe)
varies slowly too and at some time a fiducial
ecliptic with an invariant
orientation relative to said
invariable plane was established.
So the orbital inclination
of the Earth's orbit
(which is 0° relative to the true
ecliptic, of course)
varies slowly and slightly.
Nowadays we just refer to
the fiducial ecliptic as the
ecliptic
without qualification usually.
- Note planet
and planet-like
astronomical object
orbits
are close to being circles
(i.e., the eccentricities are relatively
small) and are nearly in the
ecliptic plane
(i.e., the orbital inclinations
are relatively small).
Mercury and
the degraded Pluto,
Eris,
and the hypothetical Planet Nine
are the 4
outliers in regard to
both
eccentricity
and
inclination to ecliptic.
- Eccentricity
is, among other things, the RELATIVE AMOUNT that the
Sun-planet
distance varies from the
mean orbital radius.
For example,
Mercury
goes 20.5630 % nearer and farther from the
Sun than the
mean orbital radius.
Mercury,
Pluto,
Eris
and
hypothetical
Planet Nine
have the largest
eccentricities.
- The Earth's L2 point
is in the news circa the 2020s
since the
James Webb Space Telescope
(JWST, 2021--2041?) is deployed in
a halo orbit (which is
NOT an orbit in the usual sense) about
said L2 point
(see Wikipedia:
James Webb Space Telescope: Features;
Wikipedia:
James Webb Space Telescope: Orbit - design).
The Earth's L2 point
is a point where the orbital
centrifugal force cancels
the combined gravitational forces
of Earth
and Sun to create an
unstable equilibrium
that corotates with the Earth
and does NOT obey
Kepler's 3 laws of planetary motion
(Wikipedia: Lagrange point: L2 point).
The halo orbit
is needed for obital station-keeping
in the vicinity of unstable equilibrium
and the JWST occasionally needs small
rocket
thrusts by its
thrusters to maintain
the halo orbit
(see Wikipedia:
James Webb Space Telescope: Orbit - design).
The Earth's L2 point
is just a bit beyond
the Earth's umbra extent (UE),
and so if you were exactly at the
Earth's L2 point, the
you would see a perpetual
annular solar eclipse (due to Earth, not Moon):
i.e., the dark nightside of the
Earth centered on
the disk of the Sun's
solar photosphere.
The halo orbit
of the JWST
has a radius varying
between 250,000 km and 832,000 km
(which are both much larger than the
Earth equatorial radius R_eq_⊕ = 6378.1370 km), and so
yours truly thinks
the JWST
NEVER experiences even a
partial solar eclipse (due to Earth, not Moon).
Since the JWST
is powered by solar panels,
it must received
sunlight.
However,
the JWST needs the
JWST sunshield to shield
its instruments from heating by sunlight.
It would have been convenient to prevent heating by
sunlight
if the JWST
experienced a perpetual total solar eclipse (due to Earth, not Moon)
by the Earth's
umbra.
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