Sir

I read with interest your Editorial on “Schools at 1020 eV and beyond” (Nature 429, 685; 200410.1038/429685a). We applaud the University of Nijmegen physicists for their success with the high-school project on astrophysics research with cosmics (HISPARC), which has installed cosmic-ray detectors at high schools across the Netherlands.

As the detection rate for these rare high-energy cosmic rays is in the order of one a year per square kilometre of collecting area, it is important to increase the collecting area (by increasing the number of schools involved), and so we welcome HISPARC to a growing family of similar projects across North America and Europe.

In addition, these arrays can search for coincident, nonrandom ‘hits’ across a large area that could result from correlated primary events from some of the highest-energy objects in the Universe. Again, such phenomena are expected to be very rare and would benefit from the largest collection area possible.

The first cosmic-ray project with an educational dimension was Canada's ALTA project, ‘a search in Alberta over a Large area for cosmic-ray shower Time coincidences using an Array of detectors’. This started in 1996 and the idea has been spreading across the world ever since. The ALTA network now consists of 15 sites in high schools across Alberta covering an area of some 100,000 square kilometres.

In addition to searches for cosmic-ray phenomena, the ALTA collaboration of high-school students, teachers and university researchers are pursuing investigations into atmospheric effects on the detection rate for high-energy cosmic rays. Additionally, we will be investigating the use of the arrays to monitor the soft cosmic-ray flux from the Sun — to provide an online ‘solar weather report’.

The North American projects are grouped together as the NALTA collaboration (http://csr.phys.ualberta.ca/nalta) and now cover a total collecting area of a few hundred thousand square kilometres. Similar projects in Europe include the Stockholm Educational Air Shower Array (SEASA) in Sweden and Sky-View in Germany. In addition, the Italian Extreme Energy Events (EEE) project is just getting started. A project in the Czech Republic is being jointly developed by the Czech Technical University in Prague and the University of Alberta.

Clearly, more arrays mean more opportunities for students and for science. We would like to welcome HISPARC to this family and wish it continuing success for the future.