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Astronomers have measured the passing of a super-Earth in front of a bright, nearby Sun-like star using a ground-based telescope for the first time. The transit of the exoplanet 55 Cancri e is the shallowest detected from the ground yet. Since detecting a transit is the first step in analyzing a planet's atmosphere, this success bodes well for characterizing the many small planets that upcoming space missions are expected to discover in the next few years.

The international research team used the 2.5-meter Nordic Optical Telescope on the island of La Palma, Spain, a moderate-sized facility by today's standards but equipped with state-of-the-art instruments, to make the detection. Previous observations of this planet transit had to rely on space-borne telescopes.

The host star, 55 Cancri, is located just 40 light-years away from us and is visible to the naked eye. During its transit, the planet crosses 55 Cancri and blocks a tiny fraction of the starlight, dimming the star by 1/2000th (or 0.05%) for almost two hours. This shows that the planet is about twice the size of Earth, or 16,000 miles in diameter.

"Our observations show that we can detect the transits of small planets around Sun-like stars using ground-based telescopes," says Ernst de Mooij of Queen's University Belfast in the United Kingdom, lead author of the study.

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