350 million stars

The Beijing-Arizona Sky Survey Project （BASS）， an international cooperation project between the National Observatory of the Chinese Academy of Sciences and the University of Arizona in the United States， plans to use the US 2.3-metre Bok telescope to watch the images of the G-Band and R-band inthe North Galactic Cap Sky Area of 5500 square degrees.

The BASS has released the earlier and the first versions of data in December 2015 and January 2017. After acquiring the new observational data and upgrading the data processing software completely， project members have recently released a second version of the data to the global public. The second version of the data features a position calibration accuracy of 0.03 corner seconds， a new internal calibration algorithm to correct the image anda newly developed metering software for metering. The dataalso include the Z-band data from the US-led observation for the first time.

Products generated from this second version of the data include single exposure image， single exposure star table， star Navigation， merged images and star tables and so on. Zhou Xu， Project leader and the National observatory researcher， said the combined star chart includes the metering information of 350 million stars and galaxies. “It is the star table product that covers the largest sky area in our country by now."