The pair of telescopes will now have "stereoscopic" vision
The title of largest gamma-ray telescope has passed back to the Major Atmospheric Gamma-ray Imaging Cerenkov facility on the island of Palma.
It gets the accolade as the second Magic telescope collects its first light on 25 April.
Gamma-ray radiation is emitted by the most distant, earliest galaxies and the most violent stellar processes.
Magic measures gamma rays via the particle showers they cause as they arrive in our atmosphere.
When built, the first Magic telescope was the largest gamma-ray telescope in the world, but was supplanted in 2003 by the High-energy Stereoscopic System, a four-telescope array in Namibia.
The mantle will be passed back to Hess later in 2009; this week also sees the first arrival at the Hess site of parts for Hess II, a 30m, 600-tonne successor to the original four Hess telescopes.
The Magic II telescope was due to be inaugurated in September 2008. However, the project's manager Florian Goebel of the Max Planck Institute of Physics in Munich (MPI) died while working on the telescope's camera a week before the initial inauguration date.
Telescopes like Magic and Hess detect gamma rays indirectly, by watching for Cerenkov radiation.
While the speed of light in a vacuum is the universal speed limit, each material has its own, lower speed at which light can travel through it.
Cerenkov radiation is responsible for the blue glow of nuclear reactors
Cerenkov radiation is created when fast-moving gamma rays pass through matter - in this case, the Earth's atmosphere. Gamma rays kick off a shower of fast-moving particles in the atmosphere, which in turn emit Cerenkov radiation.
This process is also responsible for the eerie blue glow of nuclear reactor cores.
"Gamma ray telescopes deal with the highest possible energies and processes that take place in the Universe," said Razmik Mirzoyan, the astrophysicist who is leader of the MPI's Magic group.
"For a given process, one needs to measure its proper messengers, so for measuring very high energies one needs to measure the photons that carry these very energies - gamma rays," he told BBC News.
The second Magic telescope will give the observatory stereoscopic vision, making experiments up to nine times faster and increasing their angular resolution by nearly a third, so that the sources of the gamma rays can be more precisely pinned down.
The telescopes will also be better poised to catch gamma-ray bursts, the showers of the rays that occur when a black hole is formed.
"For dark matter searches, our potential will strongly increase," Dr Mirzoyan added. "The pair of Magics will improve our sensitivity at energies of a few tens of gigaelectron volts, where the signatures of the dark matter could be anticipated."