At 03:57 PM 3/29/03 +0000, Alberto Monteiro wrote:
Ronn!Blankenship wrote: > >>That's the problem, isn't it? But maybe if we don't expect any two >>stars to get close enough, > >An illustration I have heard (not necessarily precise) is that two stars in >our Galaxy have about the same chance of colliding as two flies which start >from opposite ends of the Grand Canyon. > But I am not talking about _collision_. I am talking about getting close enough for enough time to change their speeds more than the initial errors in the measurement of those speeds.
And there are 100 thousand million flies, or 10 thousand trillion pairs of stars :-)
At 08:58 AM 4/1/03 -0300, Alberto Monteiro wrote:
... and now even more that it has three values:
1 USA inch = 2.something cm
1 inch = 2.54 cm.
Curse them!
But there's a coincidence that you may find interesting:
1 mile = 5280 feet * 12 inches/foot = 63,360 inches. 1 light year (ly) = 9.463 x 10^17 cm, and 1 astronomical unit (AU) 1.496 x 10^13 cm, so 1 ly = 9.463 x 10^17 cm / 1.496 x 10^13 cm/AU = 63,240 AU, which by coincidence is within 0.2% of the above number.
Thus, one can construct a scale model of the Universe where 1 inch = 1 AU and 1 mile = 1 light year.
If we put the Earth's 1 inch (2.54 cm) from the Sun, the Sun would be represented by a dot a bit under 1/100 inch (0.25 mm) in diameter. (The Earth itself is 109 times smaller, so at this scale is probably not visible without a microscope.)
Alpha Centauri will be represented by a pair of dots (one slightly larger than that representing the Sun, one slightly smaller) 4.36 miles (7.02 km) away, separated by an average of 20 inches (50 cm) (the distance between the two dots varies from 10 to 30 inches (25 to 75 cm)). Proxima Centauri would be a third dot about one-tenth the diameter of the dot representing the Sun perhaps 0.16 mi (0.25 km) away. Other stars will be represented by dots ranging in diameter from 0.001 inch to perhaps as much as 20 inches (0.25 mm to 50 cm), at an average separation of about 7 miles (11 km).
Our Milky Way Galaxy is about 100,000 ly across, so on this scale it would be represented as a disk 100,000 miles (160,000 km) across. In this space, even 10^11 - 10^12 dots have plenty of space to move around in.
The radius of the observable Universe is something like 13 billion ly, which scales to 13 billion miles (21 billion km). The semimajor axis of Pluto's orbit is 3.7 billion miles (5.9 billion km), so in our scale model the observable Universe is about three times the diameter of Pluto's orbit.
Admittedly, this model is more useful if you are accustomed to using inches and miles than if you have always used SI units . . .
-- Ronn! :)
Ronn Blankenship Instructor of Astronomy/Planetary Science University of Montevallo Montevallo, AL
Disclaimer: Unless specifically stated otherwise, any opinions contained herein are the personal opinions of the author and do not represent the official position of the University of Montevallo.
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