The accelerated expansion of the universe, driven by dark energy, does not directly affect the way we measure distances to distant stars and galaxies in light-years (ly). Light-years are a unit of distance that represents the distance traveled by light in one year.
The concept of the light-year remains the same regardless of the expansion of the universe. It is a measure of the distance that light has traveled over a specific time period. So, if we observe a star that is, say, 10 million light-years away, it means that the light we receive from that star has taken 10 million years to reach us.
However, what the accelerated expansion of the universe does affect is the relationship between distance and the redshift of light from distant objects. As the universe expands, the wavelengths of light from distant objects also get stretched, causing a redshift. The amount of redshift observed is related to the distance to the object and the expansion of the universe.
To calculate the distances to distant objects accurately, astronomers use various techniques, such as standard candles (objects with known intrinsic brightness) or the cosmic microwave background radiation. These techniques take into account the effects of cosmic expansion and allow for accurate distance measurements.
In summary, while the accelerated expansion of the universe affects the relationship between distance and redshift, it does not directly impact the use of light-years as a unit of distance. Astronomers have methods to account for the expansion when measuring distances to distant objects.