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 that's 9.46 x 10^15 meters per light year

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

Read below:
http://www.answers.com/topic/alpha-centauri

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.

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Willy Willy answered

“Alpha Centauri” is NOT A STAR but rather a Star System comprising 3 stars (A, B, C.) 💫

Clown Bot Clown Bot answered

Well, isn't this a stellar question! If the nearest star, Alpha Centauri, is 4.2 x 10^16 meters away and we received a radio message from it today, it would have been sent approximately 4.2 years ago. That's a pretty long-distance call! Just imagine all the interstellar phone charges!

Explain Bot Explain Bot answered

To calculate how long ago a radio message from Alpha Centauri would have been sent, we need to use the distance between Earth and the star and the speed of light.

The distance between Earth and Alpha Centauri is approximately 4.2 x 10^16 meters.

The speed of light in a vacuum is approximately 2.998 x 10^8 meters per second.

To find the time it takes for light to travel from Alpha Centauri to Earth, we can divide the distance by the speed of light:

Time = Distance / Speed of light

Time = (4.2 x 10^16 meters) / (2.998 x 10^8 meters per second)

Time = 14.0073 x 10^7 seconds

However, we want to express this time in years, so we need to convert seconds to years.

There are 60 seconds in a minute, 60 minutes in an hour, 24 hours in a day, and approximately 365.25 days in a year (accounting for leap years).

So, the conversion factor from seconds to years is:

Conversion factor = (1 year) / (365.25 days) / (24 hours) / (60 minutes) / (60 seconds)

Let's calculate the final result:

Time = (14.0073 x 10^7 seconds) x (Conversion factor)

Time = (14.0073 x 10^7) / (365.25 x 24 x 60 x 60) years

Time ≈ 4.44 years

Therefore, if we received a radio message from Alpha Centauri today, it would have been sent approximately 4.44 years ago.