In Hawaiian, “Haleakala” means House of the Sun. And it is precisely there, at the 3,000 metres high summit of the volcano “Haleakala”, on the Hawaiian island of Maui, that a telescope especially designed for observing the sun is currently under construction. And it’s not just any solar telescope: it’s the largest and most powerful solar telescope in the world.
“It’s a great leap forward! Previous solar telescopes have been equipped with mirrors of up to 1.50 metres in diameter. With this telescope, the primary mirror, pointing at the sun, will be over 4 metres in diameter. The larger the mirror, the sharper the images can be. The details of the surface of the sun will be twice to three times sharper”, explains Xavier Verians, director at Amos, who has participated in the construction of the telescope.
This DKIST telescope (its official name) has its roots in Belgium, or more specifically in Liège, as Amos, in collaboration with Micromega Dynamics, has constructed and has just delivered “the most important part” of the Hawaiian telescope. This “cell”, the mechanical subsystem that holds the mirror in place in the telescope, must ensure that ‘the entire telescope operates correctly’. This subsystem, which weighs 9 tonnes, must position the mirror, with a precision of a few micrometres (40 times better than the thickness of a human hair), as the telescope moves in line with the position of the sun throughout the day.
The primary mirror cell with the actuators, at the Amos workshops in Belgium.
“A boiling cooking pot”
The cell is also equipped with 142 points of contact with the mirror produced and designed by Micromega. The purpose of these small actuators is to continuously ensure the perfect shape of the parabolic mirror without them, the shape of the mirror would be distorted under its own weight of 3 tonnes and therefore ensure an accurate image. Also, given its position continuously pointing at the sun: the telescope must be protected against intense light and heat, which may interfere with the images taken. The cell should therefore control the temperature uniformity, including at noon when the mirror is fully exposed to the sun. Absorbing screens and special anti-reflective paints are also used.
With this giant telescope, the objective of the scientists is to take images in high resolution, and in quick succession, “of this boiling cooking pot, which we call the sun, continues Xavier Verians, in particular of its magnetic activity. The purpose of this is so that we can improve the monitoring and our understanding of the formation of solar flares that may interfere with electric networks and damage satellites. This is a problem that is becoming an increasing concern for space agencies.
NSO/AURA/NSF A solar flare captured by the National Solar Observatory.
World-renowned for the construction of 2 to 4 metre diameter telescopes, Amos and Micromega, have already constructed another telescope in Hawaii. This facilitated our success in obtaining this new American contract, says Xavier Verians: “There are already quite a few observatories in Hawaii. This one sits at the top of a mountain, there is therefore less atmosphere to distort the view and the image will be purer. The air in Hawaii is also very dry, with very little dust. Normally, when you look at the sun, if you hide the sun with your hand, the rest of the sky will be very white, as the atmosphere is full of dust and diffuses the sun’s light. This pollutes the image. However in Hawaii, the surrounding sky will still be very blue as there is no dust in the air. It is a high quality location.”
Source: Sophie Devillers, 2017, “Le plus grand télescope solaire du monde est belge”, La libre Belgique, Bruxelles, 19 et 20 août, p. 30 et 31.