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Scientists and other people around the world are paying their respects to Trevor Weekes, a world-renowned astrophysicist, who was considered a pioneer and visionary in the field of gamma ray astronomy.

Weekes was born in Ireland, but he moved to Southern Arizona in the 1970s, where he helped to develop VERITAS - Very Energetic Radiation Imaging Telescope Array System - on Mount Hopkins south of Tucson.

Weekes passed away May 26 at the age of 74 after a battle with cancer.

A memorial was held in Tucson on Sunday, and was attended by people from different countries, including John Kildea, who considered Weekes a mentor and friend.

Kildea met Weekes in Arizona when Kildea came to conduct postdoctoral research a few years ago.

Originally from Ireland, Kildea now lives and works in Canada.

"He welcomed students from Ireland, from other countries into his home, he and his wife Ann, and made visiting scientists part of their family," Kildea said.