Have you ever imagined what it would be like moving at the speed of light? To have the ability to travel that quickly (think ~300,000,000 m/s) would be incomprehensible — you’d experience a host of different effects, including time dilation (how more rapidly moving objects experience time more slowly), relativistic aberration (how your field of view distorts as a result of moving at such high speeds), and even the Doppler effect (changing light frequencies from high speeds). In essence, things would be very different if you chose to start traveling at around the speed of light!
However, what’s interesting is that physics dictates that it’s actually physically impossible for humans to travel at the speed of light. As a result of Einstein’s Theory of Special Relativity (E = mc^2), an object moving at the speed of light must have an infinite mass (which doesn’t seem right). So, even though humans can’t actually travel the speed of light, they can travel “almost” the speed of light, causing the host of effects listed in the paragraph above.
And, as a brief overview, the speed of light represents a fundamental physical constant used throughout Astronomy and Physics. It’s not only used in quantitatively-based equations — it’s also commonly used to describe vast distances between objects in space (as constants we use on Earth would be orders of magnitude too small to describe the distances). All in all, the speed of light serves as a significant physical quantity that manifests itself in all sorts of different parts of the sciences.