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April 10th, 2011, 05:15 AM  #1 
Newbie Joined: Apr 2011 Posts: 2 Thanks: 0  Distance to star and spatial comparison
I want to describe to my son and nephews some awareness of the size of the galaxy, universe and so on. It has been some year since I have done much math so I would appreciate if someone could check my figures. To do this I thought I would by describing the Sun as a 1mm grain of sand and then saying how far away the next star (Proxima Centauri). To this end I used figures found on the net (which seemed to vary but probably not by enough to change the outcome for my purpose). First; Found the diameter of Sun – 1391980 Km I then shrank this down to a diameter of 1mm (1/1000000 Km) so; (1/1000000)/1391980 = 7.18401E13 Okay now distance to star is 4.3 (or 4.2) ly – I found out this is about 40 million million Km. I compared this to a figure of 9.46 trillion km = 1 ly so 9.46 *4.3 = 40.678 which seems right. So to this end I took 40*1000000*1000000 and multiplied by 7.18401E13 This gave me 28.7 Km as the distance to nearest star if the Sun was a one mm grain of sand. Anyone agree? 
April 10th, 2011, 07:11 AM  #2 
Senior Member Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3  Re: Distance to star and spatial comparison
Yes, that's right. The Earth is then an almost invisible speck 10.77 cm away, and light takes five seconds to travel 1 mm. http://www.wolframalpha.com/input/?i=1m ... n+in+km%29 
April 11th, 2011, 07:51 AM  #3 
Newbie Joined: Apr 2011 Posts: 2 Thanks: 0  Re: Distance to star and spatial comparison
The light taking 5 seconds to go 1mm is the shock here. So if we use Pluto as its boundry to our system, how far out does that go (e.g. a CD is not big enough if Earth is 10cm, maybe LP or hula hoop)? I started this as I was going to beach with children soon and was going to get them to pace it out, I think making them walk 28Km is a bit much plus beach is only 4 miles long  will go to beach 28Km from home maybe. Anyone what to try Andromeda Galaxy on this scale (approx 2.5 million ly) just for fun? Thanks for info, I love these type of things! 
April 12th, 2011, 12:02 AM  #4 
Senior Member Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3  Re: Distance to star and spatial comparison
These are the average distances from the Sun, in 1000s of kilometres and then to scale in centimetres: Code: Mercury 57910 4.17cm Venus 108200 7.78 Earth 149600 10.76 Mars 227940 16.40 Jupiter 778330 55.99 Saturn 1426940 102.66 Uranus 2870990 206.55 Neptune 4497070 323.53 Pluto 5913520 425.43 On that scale the Andromeda Galaxy is then 17 503 597 km away, or over oneninth of the real distance to the Sun. 

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