Wednesday, January 26, 2022

JWST Arrival at Station L2

Environmental & Science Education, STEM, Astrophysics, Cosmology, Solar System, Earth & Space Science, History of Science, Nature of Science, Maths

As you probably know the James Webb Space Telescope (JWST) has reached its final destination where it is to explore the cosmos for 20+ years. The location is called L2, the second Lagrange Point.

Alexandra Witze has written a short essay for the British journal Nature about its arrival. It is about 1.5 million kilometres away from Earth. Witze provides another way to  try to think about that distance which is "four times the distance to the Moon." There, at this particular sweet spot in the solar system, "the combined gravitational pull of the Sun and the Earth balance the centripetal force that tugs Webb in the opposite direction."

Why this location in space? It is a unique location for investigation of the universe. Witze writes this place provides "the ability to look at most of the sky unimpeded.  Telescopes that orbit Earth, such as the Hubble Space Telescope, have a lot of their view blocked by the planet for much of the time. Facing away from the Sun, the Webb telescope can keep it, as well as Earth and the Moon, behind it. 'L2 is really nice because it’s got the brightest objects — the Sun, the Earth and the Moon — on the same side as far as the spacecraft is concerned,' says Karen Richon, an engineer who heads Webb’s flight-dynamics team at the NASA Goddard Space Flight Center in Greenbelt, Maryland. 'You can make a big sunshield and block all three of those all the time.'”

In addition, "it's cold. Earth-orbiting missions go in and out of sunlight on each orbit, experiencing huge temperature swings that cause equipment to expand and contract. Scientific instruments that have to remain cold to function do better at L2, where the temperature is much more stable. Webb’s four scientific instruments operate at temperatures of about –233 °C — or 40 degrees above absolute zero — to spot faint glimmers of heat coming from stars, galaxies and other cosmic objects."

And those LaGrange points?  Witze tells us that they "are named after their identifier mathematician Joseph-Louis Lagrange who in 1772 discovered them as locations where a small body can orbit in concert with two larger masses. That makes L1 and L2, the closest Lagrange points to Earth, obvious places to exploit for space exploration."

There is more, including a very useful box with a diagram of the sun, moon,  JWST location and all the LaGrange points.

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