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(P-1) The Solar System--Links and Tables



8. The Round Earth

  8a. The Horizon

  8b. Parallax

8c. Moon dist. (1)

8d. Moon dist. (2)

9a. Earth orbits Sun?

9b. The Planets
P-1   Planets

9c. Copernicus
        to Galileo

10. Kepler's Laws

    This section opens a collection of 13 additional sections on selected members of the solar system. This is no more than an introductory overview, supplementing "From Stargazers to Starships." Much more can be found in books and on the web, in particular in www.nineplanets by Bill Arnett (the URL dates to the time when Pluto was counted as a major planet) and in various Wikipedia web pages.
      Please note that these sections were added some 10 years after the rest of "Stargazers" was posted.
    The central question in science is not "what are the facts?" but "how do we know?" and these web pages tell of many discoveries. Such information may not have many applications (unlike the physicd and math of other sections of "Stargazers"), but they provide insight into the way science works, into its community and its instruments. Readers whose interest is aroused (may their numbers increase!) can find much more in books, web sites, astronomy clubs and journals.

    This summary (with several tabulations below) is followed by 13 additional sections:
  1. Mercury--hottest, small, closest to the Sun, moon-like, magnetic, with odd axial spin.
  2. Venus--thick atmosphere, hot, non-magnetic, very slow spin which may even be locked onto Earth.
  3. Earth--abode of life, benefiting from moderate temperatures, oceans of liquid water and nitrogen-rich atmosphere. Large moon, magnetic core and well-developed magnetosphere.
  4. Mars--the one most like Earth, but smaller, cold, very thin atmosphere, polar caps, giant volcanoes, non-central magnetism, 2 tiny moons.
  1. Asteroids--A large swarm of small orbiting rockpiles. A rare possibility exists of one hitting Earth.
  2. Jupiter--largest, most strongly magnetized, huge radiation belt, polar aurora, colorful active atmosphere
  3. Io and other Jupiter moons--4 big moons: outer ones icy, innermost Io volcanic. Many small moons and a thin ring
  4. Saturn--Second to Jupiter in mass and magnetism, famous rings, many moons.
  5. Telescopes--The astronomer's prime tool, indispensable in studying the distant solar system (and the rest of the universe). The first ones to observe the sky, in 1609, revolutionized astronomy.
  6. Uranus--Gas giant discovered 1781, axis almost in the ecliptic, magnetic axis steeply inclined to it.
  7. Neptune--Gas giant resembling Uranus, magnetic axis steeply inclined, its largest satellite in retrograde orbit.
  8. Pluto and the Kuiper Belt--Small icy planets, quite numerous.
  9. Comets and other small objects--Some come from the distant "Oort cloud," swing around the Sun, then return to deep space. Others are periodic, depleted and young, and may have come from the Kuiper belt, perhaps as "Centaur objects." And distant Sedna and (as of 2012) VP113 (aka Biden, VP of the USA), still unclassified.

Tables of the Major Planets

Note: These lists have limited accuracy. All angles are in reference to the ecliptic, the orbital plane of the Earth (or rather, the perpendicular to that plane). The orbital inclination, for instance, is the angle between the perpendicular to the orbital plane and the perpendicular to the plane of the ecliptic. Orbits of major planets are inclined only slightly to each other.

      Many entries in these tables compare properties to those of Earth. The measured values for Earth:
Mean distance from the Sun ("Astronomical Unit") 149,598,000 km (usually rounded to 150 million); Orbital period, 365.256 solar days; mean radius, 6371 km; mass 5.9736 1024kg; acceleration due to gravity 9.8 m/sec2, surface magnetic field at the equator about 30,000 nT.
      Oblateness is the ratio between (requat–rpolar) and requat. Notice also how eccentric the orbit of Mercury is!
  Planet     Mean Dist. from Sun, AU   Orbital eccentricity   Orbital period   Orbital inclination   Mean radius, rel. to Earth   Oblateness:  
  Mercury     0.381     0.2056     87.97 d.     7.005°     0.3829     small  
  Venus     0.7233     0.0068     0.6152 yr.     3.3947°     0.9499     small  
  Earth     1     0.0167     1 yr.     0°     1     0.003353  
  Mars     1.624     0.0934     1.88     1.85°     0.532     0.0059  
  Jupiter     5.204     0.04877     11.86     1.3°     10.86     0.06487  
  Saturn     9.582     0.0557     29.66     2.49°     9.0     0.098  
  Uranus     19.23     0.0444     84.32     0.77°     3.97     0.0229  
  Neptune     30.1     0.0112     164.79     1.768°     3.86     0.0171  

Note on table below: Gravity, escape velocity and absolute surface temperature are for the visible outline. At Mercury, day and night temperatures differ greatly; for the gas giants, parentheses indicate that temperature increases rapidly with depth in the observed atmosphere. Note that the rotation of Venus is very slow, and technically (minus sign) in the opposite sense.
  Planet     Mass (Earth=1)   gravity (Earth=1)   Mean density   Escape vel.   Rotat. period   Abs. surface
  Mercury     0.055     0.38     5.427    4.25 km/s    58.646 d. 100(night)
700 (day)
  Venus     0.815     0.907     5.204     10.46   –243.02 d.   735  
  Earth     1     1     5.515     11.186   1436 min     287  
  Mars     0.107     0.377     3.934     5.027   1477 min   227  
  Jupiter     317.8     (2.364)     1.326     59.5     9.925 hr.     (120)  
  Saturn     95.15     (0.916)     0.687     35.5     10.7 hr.     (88)  
  Uranus     14.54     (0.886)     1.27     21.3     17.2     (60)  
  Neptune     17.15     (1.14)     1.638     23.5     16.1     (55)  

Note on table below: Magnetic polarity opposed to Earth's is indicated by minus sign. Since all angles are relative to the perpendicular to the ecliptic, the fact that Uranus and Venus have axes tilted above 90° means that technically they spin in opposite direction from Earth. Note however that the axis of Uranus is almost in the ecliptic (inclin. near 90°), while Venus spins very slowly. Where the field is dominated by a dipole near the center, its strength is given, relative to the Earth's; note that the inclination of the Earth's magnetic axis, often quoted at 10-11°, has been rapidly decreasing in recent years.

Planet  Rotat.axis inclin   Centr. dipole (Earth=1)   Magn. axis inclin.   Moons   Surface press. (atm.)
  Mercury     ~0     ~0.0006     < 3 °   --     --  
  Venus     177.36°     ~0             93  
  Earth     23.43 °     1     ~5°    1     1  
  Mars     25.19 °     off-center         2     .007  
  Jupiter     3.13°     ~20,000     –9.6°     63     ---  
  Saturn     26.73°     ~500     ~0°     60+     ---  
  Uranus     97.77°     ~50     –59°     27     ---  
  Neptune     28.32°     ~25     –47°     13     ---  

Next Stop (following "The Planets"): #9c   The Discovery of the Solar System, from Copernicus to Galileo

            Timeline                     Glossary                     Back to the Master List

Author and Curator:   Dr. David P. Stern
     Mail to Dr.Stern:   stargaze("at" symbol) .

Last updated: 2 April 2014