ALMA looks straight into the sun
For the human eye, staring straight into the sun is a daunting (and unwise) task. For the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, peering into the heart of our nearest galactic fireball is a walk in the park, as evidenced by a series of photos just released by the European Southern Observatory (ESO) from the telescope's first direct observation of the sun. Included in the images is a close-up of a sun spot that's nearly twice the diameter of Earth.
Many earthbound telescopes need to be shielded from the sun's radiation to function properly, or at the very least, precautions need to be taken when funneling all that heat and light from the sun. In fact, according to the ESO, the now decommissioned Swedish–ESO Submillimetre Telescope actually caught on fire when it was accidentally pointed at the sun.
ALMA, however, has been designed to peer straight at our star. It uses special antennae that can simultaneously look at the sun's chromosphere, which is found just above its photosphere layer (the visible surface of the sun), while avoiding damage from the blazing beast. In imaging the sun, ALMA makes use of radio interferometry, a technique by which a series of antennae – in this case 66 of them – act together to image cosmic bodies like a solid telescope.
"The result of this work is a series of images that demonstrate ALMA's unique vision and ability to study our Sun," said the ESO in a statement. "The data from the solar observing campaign are being released this week to the worldwide astronomical community for further study and analysis."
Of particular note is the image ALMA grabbed of an enormous sunspot, an area of intense magnetic activity that is cooler than its surroundings, which makes it appear black. ALMA actually snapped two images of the sunspot – one at the 1.25 mm spectrum, seen above, and one at 3 mm, seen here.
The ESO team also used a single antenna in the array to image the full disc of the sun at the 1.25 mm spectrum in just a few minutes, using a technique called fast scanning. "These maps show the distribution of temperatures in the chromosphere over the whole disc at low spatial resolution and therefore complement the detailed interferometric images of individual regions of interest," said the ESO.
While the most impressive images of the sun are undoubtedly being returned these days by NASA's Solar Dynamics Observatory, the new ALMA data will certainly help astronomers get a more complete picture of the sun across the entire electromagnetic spectrum. Plus, the SDO has a bit of an advantage over ALMA, as it is space based rather than Earth based.
"Understanding the heating and dynamics of the chromosphere are key areas of research that will be addressed in the future using ALMA," says the ESO. Along with its newly added water-seeking instruments, the array is sure to continue helping scientists unravel the unknown elements of our cosmic neighborhood and beyond.