Egged on by some of Kraig's criticisms and given a boost by the astronomy links Paul posted, I decided to hunt down more precise info on the planets's orbital periods, and to make a more accurate version of 'Solar System'. Here it is: http://www.egroups.com/files/tuning/monz/solarsystem/Solar2.mid There's not a lot of difference, but to my ears, this version is a bit more strident, and brings out the 'major chord' quality of the orbital-period ratios even more strongly. Thru my speakers, I can't hear Pluto or Neptune at all, and can just barely discern Uranus at the bottom and Mercury at the top when I turn off all the other planets. I'll leave these four planets out of my analysis. The 'major chord' effect is due mainly to Saturn, Jupiter, and Venus, with Mars reinforcing Saturn 4 '8ves' higher. Earth adds most of the piquancy with a pseudo-'major 7th'. So the aural effect (at least as I hear it; 'your mileage may vary') causes Saturn to sound as the 1/1 - it is actually almost exactly 3 '8ves' and a 135/128 5-limit 'semitone', or what Ellis called the 'larger limma' (92 cents), above the inaudible Pluto. Jupiter is 1 '8ve' and 375 cents higher than Saturn - pretty darn close to an '8ve' + 5/4. Mars is about 37 cents below the 4th '8ve' above Saturn. It's also 2 '8ves' and 788 cents above Jupiter. Earth is 4 '8ves' and 1057 cents above Saturn - pretty close to one of my favorite intervals, an 11/6 'neutral 7th' (= 1049 cents). To my ears, the more important audible relationship is that between Mars and Earth: 1094 cents, only 6 cents wider than a 15/8 'major 7th'. I think this stands out quite strongly in the chord. Earth is also 3 '8ves' + 682 cents above Jupiter. Venus is very high and bright, almost exactly a 13/8 above Earth (altho to my ears it really sounds a lot like an 8/5 'minor 6th'), an '8ve' + 735 cents above Mars, 4 '8ves' + 323 cents above Jupiter (pretty close to a 6/5 'minor 3rd'), and 5 '8ves' + 698 cents (a nice meantone '5th'!) above Saturn. Here's the more accurate data, which supercedes the tables in my original post: Orbital period days years Mercury 87.969 0.24084 Venus 224.701 0.615187 Earth 365.256363 1.0 Mars 686.98 1.8808 Jupiter 4332.71 11.8621 Saturn 29.458 Uranus 84.01 Neptune 164.79 Pluto 248.54 The figure given for the Earth's orbital period is known as the 'sidereal year': the time it takes for the Earth to make a complete revolution with respect to the stars. It can also be expressed as 365 days 6 hours 9 minutes 9.76 seconds. All 'year' values are given in terms of sidereal years. I really had to hunt for an accurate value for this, and finally found it at http://www.treasure-troves.com/astro/SiderealYear.html This is different from the 'solar' or 'tropical year', which is the one we're normally familiar with. This is the time it takes for the Earth to make a complete revolution with respect to the Sun's position in our sky. The solar year is 365.2421988 days, or 365 days 5 hours 48 minutes 45.9747 seconds. It is 20 minutes 23.5 seconds shorter than the sidereal year. (Our standard system of leap-years gives a solar year 365.2425 days long, as described at the link above. This means that after 3,319 years 10 months, we will lose a day.) Again, these are also mean values, because they change slightly over time. Here is a table of the semitone values of the orbital ratios: SEMITONES Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto Mercury 0.00 16.24 24.65 35.58 67.47 83.21 101.36 113.02 120.13 Venus 0.00 8.41 19.35 51.23 66.98 85.12 96.78 103.90 Earth 0.00 10.94 42.82 58.57 76.71 88.37 95.49 Mars 0.00 31.88 47.63 65.77 77.44 84.55 Jupiter 0.00 15.75 33.89 45.55 52.67 Saturn 0.00 18.14 29.81 36.92 Uranus 0.00 11.66 18.78 Neptune 0.00 7.11 Pluto 0.00 Note that this time I accepted the period of 248.54 years for Pluto, because the majority (and most recent) of the webpages I've found use that figure. Can anyone verify the correct value for Pluto? In any case, the pitch I chose for Pluto's 1/1 is so low that I can't hear it on my system, and most likely neither can anyone else. Such is the fate of our cold little faraway planetoid... -monz http://www.ixpres.com/interval/monzo/homepage.html