Imagine a planet 15 light-years away from Earth that is inhabitable by humans like us they have developed a very powerful telescope allowing them see what is happening on Earth if they look to the telescope today what year would it be on earth would they be able to see you explain

S defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). so if a planet 15 light-years away from Earth that is inhabitable by humans like us they have developed a very powerful telescope allowing them see what is happening on Earth if they look to the telescope today, they will see 15 years ago in the earth