All the space-related words you need to add to your vocabulary

With this, you can take part in the future discussions about the subject with some familiarity

By Shashi Tharoor

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Published: Thu 31 Aug 2023, 6:26 PM

The news of India’s Chandrayaan-3 space mission reaching the moon’s south pole has had everyone, seemingly, talking about space. This has taxed the vocabularies of many of us, so I thought it might be useful to devote this week’s column and the next to some basic words about space, so that readers can participate in this and future discussions about the subject with some familiarity!

First of all, what’s the difference between the terms “universe” and “space”? The universe refers to everything that exists: all celestial objects, the entirety of all physical matter and energy, solar systems, planets, galaxies, in short everything up there and around us, whereas space refers to the void that exists between celestial objects and is therefore a part of the universe. Space is a vacuum comprising a low density of particles, mainly a plasma of hydrogen and helium. It also includes magnetic fields, electromagnetic radiation, neutrinos, dust and cosmic rays, all of which (except dust!) we define below. Though there are many galaxies in the universe (the Earth is part of a galaxy called “the Milky Way”), most of the volume of the Universe is the space between these galaxies, or intergalactic space. In most galaxies, 90 per cent of the mass is in an unknown form called “dark matter”, which interacts with other matter through gravitational forces.

There are four kinds of space we talk about near Earth: geospace, the region of outer space near our planet, including the upper region of the atmosphere and the magnetosphere; interplanetary space, the space around the planets and the Sun of our solar system; interstellar space, the space within a galaxy that is not occupied by planetary systems or stars, which spreads to the edges of the galaxy and fades into the intergalactic void (see the film Interstellar); and intergalactic space, the space between galaxies, with vast cosmic voids that not even science fiction has yet dared to explore.

In describing these basics we’ve used a few very basic terms that everyone should know:

*Planet: A celestial body such as Earth or Mars, moving in an elliptical orbit around a star.

*Star: A celestial body that generates light and other radiant energy.

*Solar System: The Sun and all objects, including planets, asteroids, comets, orbiting around it.

*Galaxy: A gigantic collection of many stars, along with dark matter, cosmic gas and dust.

*Magnetic Field: A magnetic field is the area around a magnet where the attractive or repulsive force of a magnet can be felt.

*Electromagnetic radiation is an electric and magnetic disturbance travelling through space at the speed of light.

*Atoms are the building blocks of the Universe. All matter is made of these tiny nano-particles, so small that each human body contains billions and billions of atoms.

*Neutrinos are tiny, nearly massless sub-atomic particles that travel at near lightspeeds and rarely react with normal matter. Born from violent astrophysical events like exploding stars and gamma ray bursts, they are abundant in the universe, move through anything and interact very weakly with matter, so they very rarely leave a trace. Vast amounts of neutrinos pass through us every day, but we do not feel them because neutrinos hardly ever interact with the atoms that make up our bodies.

*Cosmic rays are high energy particles that move through space at nearly the speed of light. Most cosmic rays are atomic nuclei stripped of their atoms, with protons being the most abundant. Cosmic rays are a form of radiation that is constantly raining down on us from space. They are made up of electrically charged, subatomic particles that crash into our atmosphere, where they are broken up and fall to Earth in even smaller fragments.

*Dark matter is composed of particles that do not absorb, reflect, or emit light, so they cannot be detected by observing electromagnetic radiation. Dark matter has gravity, but it cannot be seen directly, though we know that dark matter exists because of the effect it has on objects that we can observe directly. Together, dark matter and dark energy make up most of the universe — in fact 95 per cent of it. That only leaves 5 per cent for all the tangible matter and energy that we on earth know and understand.

More next week!

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