Some of you asked recently why are #Webb's mirrors hexagonal? Thread 👇
📷 NASA/Chris Gunn
1/ The hexagonal shape enables a roughly circular, segmented mirror with "high filling factor and six-fold symmetry." High filling factor just means the segments fit together without gaps, which would not be the case if the segments were circular
2/ Symmetry is good because only 3 different optical prescriptions (A, B and C) are needed for 18 segments, 6 of each as seen below 📷 NASA
3. A roughly circular overall mirror shape focuses the light into the most compact region on the detectors. An oval mirror would give images that are elongated in one direction while a square mirror would send a lot of the light out of the central region #WebbSeesFarther

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More from @ESA_Webb

Feb 2
Taking #Webb's temperature 🌡️ 5 new temperature monitoring points have been added to the NASA website to track cooling and status of the instruments during the post L2 arrival commissioning process. Let's have a look at them 👇
1/ Temperature control is a vital aspect of #Webb 's design, engineering and operations. On the page you can see 2 "hot side" and 2 "cold side" temperatures and a set of bellweather instrument temperatures
2/ The instruments are located within the Integrated Science Instrument Module and the Fine Steering Mirror is located within the protrusion in the center of the primary mirror Image
Read 7 tweets
Jan 30
As #Webb is going through the focusing of its mirrors, let's look into what this process entails. #WebbSeesFarther 👇
1/ #Webb's 18 hexagonal mirrors have already been unfolded a while back, but now it's time for a more precise alignment so they point in exactly the same direction 🎯 and deliver sharp images.
📷 NASA/Chris Gunn Image
2/ These corrections are made through a process called 〰️ wavefront sensing and control, which senses and corrects any errors in the telescope's optics, aligning the mirrors to within tens of nanometres
Read 8 tweets
Jan 24
1/ While we wait for news on L2 orbit insertion, we've got some facts for you on #Webb's orbit 👇
2/ Unlike @Hubble_Space #Webb will not be in orbit around the Earth, but will orbit the Sun, 1.5 million km away from the 🌍 at what is called the second Lagrange point or L2.
3/ This orbit lets the telescope stay in line with the Earth as it moves around the Sun. This allows the satellite's large sunshield to protect the telescope from the light and heat of the Sun, Earth and Moon.
Read 16 tweets
Jan 24
As we approach final destination, let's take a moment to recap all the incredible steps #Webb went through so far. Thread 👇
1/ Webb's journey to space started in French Guiana, at the European Space Port. Here's why this was an ideal launch side for #Webb
2/ On Christmas Day 🎄, @Ariane5 made a flawless launch of the James #Webb Space Telescope. #WebbThanksAriane
Read 21 tweets
Jan 23
1/ The Mid-InfraRed Instrument #MIRI is one of 4 instruments on the James #Webb Space Telescope. The only mid-infrared instrument in its instrument suite. #WebbSeesFarther
📷 NASA/ Chris Gunn
2/ Thanks to state-of-the-art instrument design and components, it will deliver mid-infrared images and spectra with an unprecedented combination of sharpness and sensitivity. #WebbSeesFarther
3/ #MIRI will be capable of penetrating thick layers of dust obscuring regions of intense star birth. It will see the first generations of galaxies to form after the #BigBang, and it will study sites of new planet formation and the composition of the interstellar medium.
Read 4 tweets
Jan 22
1/ #NIRSpec has three modes of operation: multi-object spectroscopy mode, fixed slits spectroscopy mode and integral field spectroscopy mode:
2/ 🔴 multi-object spectroscopy mode — #NIRSpec will be the 1st multi-object spectrograph in space, able to record the spectra of up to 200 objects at the same time. A capability enabled by microshutters.
3/ 🔴 fixed slits spectroscopy mode — #NIRSpec will also be able to carry out single-object, high-contrast spectroscopy using a set of five fixed slits. It will provide high contrast spectra of sources and a key to the study of exoplanets.
Read 4 tweets

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