 |
2.7.3 The Solar System
Dimensions, etc., of Sun, Moon and
planets
|
Body |
Equatorial
radius |
Mass |
Surface
gravity |
|
Flattening |
Period
of
rotation |
Inclination
of equator
to orbit
|
Number
of known
satellites |
|
(on scale: Earth =
1)† |
|
|
|
|
|
|
|
|
|
|
|
Sun . . . |
109.12 |
332 946 |
27.96 |
1.41 |
0.0 |
25d 09h |
7°. |
— |
|
Mercury |
0.382 |
0.0553 |
0.38 |
5.43 |
0.0 |
58d 16h |
0°.0 |
0 |
|
Venus . |
0.949 |
0.8150 |
0.90 |
5.24 |
0.0 |
243d 00h |
177°.3 |
0 |
|
Earth . . |
1.000 |
1.0000 |
1.00 |
5.52 |
0.0034 |
23h 56m |
23°.4 |
1 |
|
Moon . . |
0.272 |
0.0123 |
0.17 |
3.34 |
See note 4 |
27d 08h |
1°.5 |
— |
|
Mars . . |
0.532 |
0.1074 |
0.38 |
3.94 |
0.0052 |
24h 37m |
25°.2 |
2 |
|
Jupiter . |
11.19 |
317.89 |
2.54 |
1.33 |
0.0648 |
9h 50m |
3°.1 |
16 |
|
Saturn . |
9.41 |
95.18 |
1.07 |
0.70 |
0.1076 |
10h 14m |
26°.7 |
18 |
|
Uranus . |
3.98 |
14.50 |
0.9 |
1.30 |
0.030 |
15h 34m |
97°.9 |
15 |
|
Neptune |
3.81 |
17.24 |
1.2 |
1.76 |
0.026 |
18h 26m |
29°.6 |
8 |
|
Pluto . . |
0.23 |
0.0025 |
0.05 |
1.1 |
0.0 |
6d 09h |
117°.6 |
1 |
|
|
|
|
|
|
|
|
|
|
|
|
† For Earth values
see section 2.7.4.
|
|
|
Notes: |
|
(1) |
The Sun is a star of spectral type G2V and
absolute magnitude +4.79. The effective temperature of its photosphere is about
5800 K. The radiation emitted per unit area is 63.3 MWm−2,
giving a total emission rate of 3.85 × 1026 W. The radiation
received at the Earth under standard conditions (i.e. the solar constant) is
1.37 kW m−2. |
|
(2) |
The periods of rotation of the Sun, Jupiter
and Saturn refer to their equatorial visual regions; the periods increase with
latitude. |
|
(3) |
The inclinations of the equators of the Sun
and Moon are referred to the ecliptic; the inclination of the equator of the
Moon to the plane of the Moon’s orbit around the Earth is about 6°.7
and the axis of rotation precesses at the same rate as the line of nodes of the
orbit (period 18.6 years). |
|
(4) |
The mean radius of the Moon may be taken as
1738.0 km, but the irregularities in the surface are of the order of 1/500 of
the radius; the principal moments of inertia are all
different. |
Mean elements of the orbits of the
planets
|
Planet
|
Mean distance
from Sun |
Sidereal
period |
Synodic
period |
Inclination
to ecliptic |
Eccentricity
|
Longitude
|
Longitude
of perihelion |
| |
au |
Gm |
year |
day |
degree |
|
degree |
degree |
|
|
|
|
|
|
|
|
|
|
|
Mercury . . |
0.387 |
57.9 |
0.241 |
116 |
7.005 |
0.2056 |
48.3 |
77.5 |
|
Venus
. . . |
0.723 |
108.2 |
0.615 |
584 |
3.394 |
0.0068 |
76.7 |
131.6 |
|
Earth + Moon |
1.000 |
149.6 |
1.000 |
– |
0.0 |
0.0167 |
– |
102.9 |
|
Mars
. . . |
1.524 |
227.9 |
1.881 |
780 |
1.850 |
0.0934 |
49.6 |
336.1 |
|
Jupiter
. . . |
5.203 |
778.3 |
11.857 |
399 |
1.303 |
0.0485 |
100.5 |
14.3 |
|
Saturn
. . . |
9.555 |
1429 |
29.42 |
378 |
2.49 |
0.055 |
113.7 |
93 |
|
Uranus . . . |
19.22 |
2875 |
83.75 |
370 |
0.0773 |
0.046 |
74.0 |
173 |
|
Neptune . . |
30.11 |
4504 |
164 |
367 |
1.770 |
0.009 |
131.8 |
48 |
|
Pluto
. . . |
39.54 |
5916 |
248 |
367 |
17.13 |
0.249 |
110.3 |
224 |
|
|
|
|
|
|
|
|
|
|
| |
Notes: |
|
(1) |
The planetary orbits are subject to both
secular and periodic perturbations, so that the osculating elements at any
instant may differ in the end figures from the elements for 2000 that are given
above. |
|
(2) |
The values given for Earth + Moon refer to
motion of their centre of mass, which lies about 4700 km from the centre of the
Earth. The mean distance between the centres of the Earth and Moon is 384 400
km; the mean eccentricity of the relative orbit is 0.055 and its mean
inclination to the ecliptic is 5°.2. The orbit is, however, subject to
considerable perturbations. The line of nodes moves around westwards once in
18.6 years, and so the inclination of the orbit to the Earth’s equator
(and hence the extremes of declination in any month) varies between 28°.6
and 18°.3. |
References
Annual tabulations of astronomical data and ephemerides
will be found in: The Astronomical Almanac (USGPO, Washington; HMSO,
London), The Handbook of the British Astronomical Association, The
Observer’s Handbook (Royal Astronomical Society of Canada), and
Whitaker’s Almanac. The booklet Astronomical Phenomena
contains extracts from The Astronomical Almanac, such as the dates and
times of planetary and lunar phenomena and other astronomical data of general
interest, and is published by HMSO several years in advance. The volume
Planetary and Lunar Coordinates, 1984–2000 (HMSO)
contains heliocentric, geocentric, spherical and rectangular coordinates of the
Sun, Moon and planets, eclipse data, and auxiliary data, such as orbital
elements and precessional constants, for use in advance of the almanacs and for
other purposes.
Extended lists of astronomical data and other
information are given in: C. W. Allen (1977) Astrophysical Quantities,
The Athlone Press, London; K. R. Lang (1992) Astrophysical Data,
Springer-Verlag, Berlin; and I. Ridpath (ed.) (1989) Norton’s 2000.0:
Star atlas and reference handbook, Longman, London.
The Explanatory Supplement to the Astronomical
Almanac (see end of section 2.7.2) contains much additional physical and
orbital data on the planets and on their satellites and rings. The
Astronomical Almanac also contains lists of positional and other data on a
wide variety of celestial objects, including stars, star clusters, bright
galaxies, radio sources and X-ray sources.
G.A.Wilkins
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