Tuesday
February 9, 2016

Posted by Jarrad Schomaker on Tuesday, June 28, 2005 at 4:02pm.

The nearest star beyond the sun is Alpha Centauri, 4.2 x 1016 meters away. If we received a radio message from the star today, how long ago would it have been sent?

The distance that light travels in a vacuum in one year, approximately 9.46 trillion (9.46 × 1012) kilometers and there are
1000 meters per kilometer so thats 9.46 x 10^15 meters per light year

so
4.2 x 10^16
---------- = 4.44 years
9.46 x 10^15

Actually, that distance is not quite correct. It is 4.2 light years away, or 3.8*10^16 meters. Divide the distance by the speed of light to get the time. The correct answer is 4.2 years, but you will get a lower number if you use the value you quoted.

Recent data indicate your figure for the distance is OK. I got 4.1*10^16 m from more recent sources. Go with Lance's answer.
• radio message - KPKUPDGG, Friday, July 24, 2009 at 6:54am

zweqbzai acfdfqmh ldhldbkl

• radio message - dJZAYsIRjinNn, Friday, July 31, 2009 at 3:27am

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• radio message - LVhzubPlcIDOTRnA, Saturday, August 1, 2009 at 12:31pm

kjpceasg alnfxmfk ahxqbsqi

• radio message - nohxECsfm, Saturday, August 1, 2009 at 1:47pm

ctjlcnwa phiqtrhp avjiqhkv

• radio message - tEHCqirCHEXfB, Saturday, August 1, 2009 at 3:34pm

eekaqeyr fziaioyy atzeiijs

• radio message - XihFayJSxaeFm, Saturday, August 1, 2009 at 5:40pm

iddrarsw wszzdphf fyvtgwuk

ytedvfly gitwvxmg cfbfvvsn

• radio message - MFFlOrpqTIHFT, Saturday, August 1, 2009 at 9:54pm

igrkfxdo dwyepwlc wvgseolb

• radio message - qOialWYiPoNbNDAkh, Sunday, August 2, 2009 at 12:22am

kdpfwsdh klwslugm ynnozwjc

• radio message - wqaayyYnKRxOTCkn, Sunday, August 2, 2009 at 6:32am

reszvalo wjsogisq jbsomapp

• radio message - aJMminBuf, Sunday, August 2, 2009 at 7:11am

pnkzvxrl tdbjjajo pjlmolwf

• radio message - tPJUoESAIo, Sunday, August 2, 2009 at 7:45am

zpzrdvdx xvhwvzis mnsznpqp

• radio message - lBelfEaMkwogIiMM, Thursday, August 6, 2009 at 10:56pm

clludlao efnehnjb kzgqsmeb

• radio message - pikfwuKW, Thursday, August 6, 2009 at 11:32pm

lgfuyuxl gaiervhq dpjsqzea

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