A global network of telescopes for monitoring gravitational microlensing events around the clock has been operated by the PLANET group since 1995. This has been utilised to monitor some events alerted by the MOA group. The MOA group is in the process of forming a second network, shown below.

Observatories that the MOA group issues alerts to of selected microlensing events for intensive follow-up. The Mt John observatory appears at the far right. Others are the Wise observatory in Israel, the Boyden and SAAO observatories in South Africa, the MDM and MONET observatories in USA, the CIDA observatory in Venezuela, and the CTIO, EROS and ESO observatories in Chile. The Hubble Space Telescope has also carried out follow-up observations.

An extensive follow-up network is required to ensure complete coverage of particular features in microlensing events that can provide information on the source and lens stars, as a guard against cloudy weather at some sites. 

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Microlensing Observations in Astrophysics