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Chapter: 2 General physics
    Section: 2.7 Astronomy and geophysics
        SubSection: 2.7.3 The Solar System

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2.7.3 The Solar System

Dimensions, etc., of Sun, Moon and planets

Body

Equatorial
radius

Mass

Surface
gravity

Mean
density

Mg m−3

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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