As stars go, pulsars are tiny, only about \(20 \mathrm{~km}\) across. Name three specific things or places that have a size or a separation of about \(20 \mathrm{~km}\).

Imagine looking out into the abyss of space and encountering some of the universe's most bizarre and fascinating objects. Pulsars, one of astronomy's gifts, are the lighthouses of the cosmos, emitting beams of radiation that appear to pulse as they rotate. These celestial beacons have been crucial to our understanding of cosmic phenomenons.

Pulsars are rapidly spinning neutron stars, the dense remnants left behind after a massive star explodes in a supernova. Though they span only about 20 kilometers across, their masses are often comparable to that of our Sun, resulting in an incredibly high density. As pulsars rotate, the lighthouse-like beams of electromagnetic radiation sweep around, and if Earth happens to be in the line of sight, we perceive them as pulses, hence their name.

Astronomy leverages the stable and precise timing of pulsar flashes to study forces at play in the universe, refine the maps of our galaxy, and even test the laws of physics. The Crab Pulsar, for example, is a well-studied celestial object, which provides us with insights about the lifecycle of stars and the extreme physics in outer space.

Neutron stars, the source of pulsars, are titans of the universe with properties that defy our daily experiences. Born out of the cataclysmic explosion of a dying massive star, known as a supernova, these stellar remnants are an astrophysicist's dream to decipher.

The density of neutron stars is almost incomprehensible—their core is so dense that a sugar-cube-sized amount of this material would weigh about a billion tons on Earth. This immense density arises because their matter has been compressed into the smallest space possible, making them essentially giant atomic nuclei.

In addition to their density, neutron stars have extremely powerful magnetic fields and spin at speeds unimaginable, with some rotating hundreds of times per second. Understanding neutron stars brings us closer to understanding the fundamental properties of matter under the most extreme conditions imaginable in the universe.

Grappling with the vastness of space requires a comprehensible scale. One of the core challenges in astronomy is measuring cosmic distances, which is essential for mapping the universe and determining our place within it.

Interestingly, the size of pulsars offers a tangible comparison to help illustrate these immense distances. For instance, the small separation between certain cities or the diameter of the world's largest volcanic crater are mere 20 kilometers wide, sizeable measurements on our human scale but minuscule on the cosmic scale.

Astronomers use a variety of techniques to measure distances in space, including parallax, standard candles like supernovae or cepheid variables, and even the timing of pulses from pulsars themselves. These methods help us understand the scale of our galaxy and beyond, from the orbital radius of our own Moon to the expansion of the universe itself. By learning more about cosmic distances, we acknowledge how marvelously vast the cosmos is, which can be both humbling and exhilarating.