How Did William Herschel Discover Such Far Away Galaxies Like NGC 7678 in 1784?

Introduction

William Herschel, a renowned astronomer of his time, was known for his significant contributions to astronomy, including the discovery of Uranus and his work on nebulae. In 1784, he managed to discover a galaxy called NGC 7678, which is 160 million light years away. This discovery was remarkable given the limitations of telescopic technology at the time. Let us explore how Herschel achieved this feat.

T reconciling the Distance and the Telescope

It is important to note that, in terms of our galactic neighborhood, NGC 7678 is not exceptionally far away. Compared to most distant galaxies, it is relatively closer to us, much like the Andromeda Galaxy, which is around 2.5 million light years away. However, it is still incredibly far, requiring a powerful telescope to observe effectively.

The Andromeda Galaxy, often referred to as M31, is the closest large galaxy to Earth, offering a great contrast in apparent size and visibility. Even though Andromeda appears large and can be seen with the naked eye, it appears small because only the bright central region is what we can see without magnification. NGC 7678, being about 60 times further away, would have an apparent size that is 1/60th as wide and 1/3600th as bright as Andromeda. Therefore, seeing NGC 7678 would require a telescope capable of magnifying the image 60 times and brightening the image a few thousand times.

William Herschel’s Revolutionary Telescope

Herschel built a telescope that was, for nearly half a century, the largest in the world. This telescope had a 40-foot length and a 48-inch diameter mirror. The size and quality of the mirror, combined with the telescope’s length, enabled it to collect enough light to see objects many times dimmer than the naked eye could perceive. This telescope was more than adequate to observe distant galaxies like NGC 7678.

The Discovery Process

At the time, Herschel did not know what galaxies were or how far away they were. His observations were based on the observation of bright, blurry spots in the sky, and he couldn’t distinguish whether they were individual stars, star clusters, or collections of stars forming a galaxy. Despite the lack of accurate distance measurements, Herschel was able to see these distant light sources using his powerful instrument.

Implications and Discoveries

Herschel's discovery of NGC 7678 not only demonstrated the potential of his telescope but also marked a significant milestone in the understanding of the universe. Herschel continued his work, leading to the discovery of several other celestial bodies, including Uranus, and contributing to our understanding of nebulae as collections of stars.

In a nutshell, Herschel's telescope, which was a monumental technological achievement for its time, allowed him to discover and observe distant, previously unknown galaxies, including NGC 7678, which is 160 million light years away. His work greatly advanced astronomy and our understanding of the universe.