A textbook published in 1945 stated that light takes 800,000 years to reach Earth from the Andromeda Galaxy. In this book, we assert that it takes 2,500,000 years. What does this difference tell you about a scientific "fact" and how our knowledge evolves with time?

The Andromeda Galaxy is a massive spiral galaxy, much like our own Milky Way. It is the nearest major galaxy to the Milky Way and is on a collision course with us, although the impact will not happen for billions of years. The Andromeda Galaxy contains over a trillion stars and is a key object of study in astronomy.
Its proximity and size allow scientists to study its characteristics in great detail. Historically, the distance to Andromeda has been a topic of much debate and refinement as technology and methodologies have evolved.
Early estimates of the distance were significantly lower than they are now because earlier scientists had less precise tools and limited knowledge about the universe.

The speed of light is a constant that plays a crucial role in our understanding of physics and the universe. It is roughly 299,792 kilometers per second in a vacuum. This figure is key to calculating astronomical distances and understanding how far away celestial objects are.
For example, if an object is 1 light-year away from Earth, it means the light from that object takes one year to reach us. Over vast distances, such as between galaxies, this measurement helps astronomers estimate how long light has traveled, revealing the age and distance of objects in the universe.
The more accurate our measurement of the speed of light, the better we can determine distances across space.

Astronomical distances are so vast that they are often challenging to comprehend. Light years, the distance that light travels in one year, are used to measure these immense stretches between celestial bodies.
Astronomers also use parsecs, where one parsec equals about 3.26 light-years, to define large distances. Various methods, such as parallax and redshift, help determine these distances.
Parallax involves observing an object from different points in Earth's orbit to measure its distance, while redshift examines how light from an object stretches as it moves away from us, helping to infer its distance. It is important to note that these methods have improved over time, leading to more precise measurements.

Scientific evidence updates reflect the evolving nature of our understanding of the universe. As new technologies develop and better observations are made, what were once considered 'facts' may change or be refined.
The example of the distance to the Andromeda Galaxy is a perfect illustration. In 1945, limited technology led to an estimate of 800,000 years for light to travel from Andromeda to Earth. Today, advanced tools and methods provide a more accurate estimate of 2,500,000 years.
This shift underscores how scientific knowledge is not static but continually evolving. It's based on the best evidence available at the time, and as that evidence improves, so does our understanding of the world around us.