An asterism is a recognizable pattern in the night sky from Earth and “El Carro” is, without a doubt, one of the most characteristic. In this asterism of the Ursa Major constellation we will find HD 84406, the star that will become the first objective of the James Webb telescope.
Webb’s first target
The main star is approximately 260 light-years away from Earth.
“While it will be too bright for Webb to study once the telescope is focused, it is a perfect target for Webb to collect engineering data and begin mirror alignment,” JWST scientists Jonathan Gardner and Alexandra Lockwood explain, in a NASA post on Twitter.
This historic telescope has to cool down and undergo weeks of calibration work to ensure that the main mirror’s 18 segments, the 18 gold-plated hexagons, ‘work as one’.
After reaching its orbit, at the second Lagrange point (L2), NASA has revealed what its first target will be: HD 84406, a star similar to the Sun, of seventh magnitude, outside the level visible from Earth with the naked eye. This goal is likely solely for engineers to collect data to begin mirror alignments.
18 separate, unfocused images of HD 84406 will be captured using each of the mirrors; then an algorithm will determine exactly how each should be oriented to focus the telescope.
According to NASA, the initial mirror alignment process is expected to take several months to complete. And they will likely need to be recalibrated every few days.
The target star has a surface temperature of about 5,000 K (our Sun is at 5,778 K); it is about 4.4 times the size of the Sun and 11 times more luminous , and could be part of a binary pair, according to data from ESA’s Gaia telescope.
