Overview 
In a vacuum, light, an electromagnetic wave, moves at an astounding 299,792 kilometers per second (km/s). When astronomical distances are taken into account, this incredible speed is not instantaneous. We need to study how long it takes light to travel from the Sun to Earth and from far-off stars to our planet in order to truly comprehend the immensity of space. 
The Path of Light from the Sun to Earth 
Our closest star, the Sun, is located approximately 149.6 million kilometers (93 million miles) from Earth. An astronomical unit (AU), a common unit of measurement used in astronomy to define distances inside our solar system, is what this distance is known as. Since light moves at a speed of around 300,000 km/s, we can determine how long it takes for sunshine to ,

Light Traveling to Earth from Far-Off Stars 
The distances between stars outside of our solar system are unfathomably large, expressed in light-years as opposed to kilometers or astronomical units. The distance that light travels in a year, or roughly 9.46 trillion kilometers (5.88 trillion miles), is called a light-year. 
Closest Star: Proxima Centauri 
The nearest star to the Sun, known as Proxima Centauri, is located 4.24 light-years away. To understand this separation:
4.24 years is the time.
Therefore, Proxima Centauri's light that we see today actually left the star 4.24 years ago. More distant stars and galaxies add to the fascination of this idea, known as the look-back time.
The Milky Way stars 
Our home galaxy, the Milky Way, has a diameter of roughly 100,000 light-years. It is possible for stars in the Milky Way to be thousands of light-years away from Earth. One of the brightest stars in the night sky, Deneb, for example, is 2,600 light-years away. By looking at Deneb, we may view the world as it was in the early Roman Republic, about 2,600 years ago. 
Beyond-Stellar Light Travel 
The distances outside our galaxy increase exponentially. Our closest spiral galactic neighbor, the Andromeda galactic, is located at 2.537 million light-years away. Andromeda appears to us as it did more than two million years ago, when the planet's first human ancestors walked around.

Consequences of Light Travel Duration 
Comprehending the duration required for light to reach Earth from stars carries significant consequences for the fields of astronomy and cosmology. Here are a few crucial elements: 
Historical Observation: We may examine the past and learn about the universe's history by looking at far-off stars and galaxies. An object's light gives us an older glimpse into the past the farther away it is from us. 
Cosmic Scale: The enormous scope of the universe is highlighted by the concept of light-years. Light travels across star and galaxy distances so great that it takes years, centuries, or even millennia to travel across them. 
Astronomical Measurements: Astronomers may determine the distances to stars and galaxies using parallax, standard candles, and redshift, among other techniques.