Kepler / K2

A 0.95 m Schmidt telescopeSchmidt telescopeA wide-field design: a spherical primary mirror with a thin corrector plate at its centre of curvature, giving sharp images over several degrees. Used by survey instruments such as ZTF and Kepler. with 42 CCDsCCDCharge-coupled device: a silicon pixel array that stores photo-electrons and shifts them to a readout amplifier. The workhorse optical detector; in X-rays, each photon's charge also measures its energy. over a 115 deg²square degreeUnit of solid angle: one degree by one degree on the sky. The whole sky is about 41,253 deg²; the full Moon covers about 0.2 deg². field measured about 150,000 stars at 30-minute cadencecadenceThe interval between successive measurements of the same field or target. Sets which variability timescales a time series can resolve: TESS reaches 20 s, Rubin revisits each field every few nights. (1 minute for a small subset) with photometricphotometryMeasuring the flux of a source in a passband. Aperture photometry sums pixels inside a region; PSF photometry fits the point-spread function; forced photometry measures at a position fixed in advance, whether or not a source is detected there. precision of tens of ppmppmParts per million of a star's flux; the unit of precision for transit and asteroseismic photometry. on transittransitA planet passing in front of its star and blocking a fraction (R_p/R_*)² of its light, about 84 ppm for an Earth across the Sun. Repeated transits give period and radius; spectra taken during transit probe the planet's atmosphere. timescales. Four years of near-continuous data showed that small planets are common and produced more than 2,600 planet discoveries. After its second reaction wheel failed in 2013 it continued as K2, balanced against solar radiation pressure in campaigns of about three months along the eclipticeclipticThe plane of Earth's orbit projected on the sky; the Sun, Moon and planets stay close to it. Solar-system bodies and zodiacal light concentrate there, and spacecraft that must keep the Sun at a fixed angle often observe in strips perpendicular to it, so the ecliptic poles get the deepest coverage..

Operator

NASA

Orbit

Earth-trailing solar orbit

Aperture

0.95 m Schmidt telescope

Passband

420 nm – 900 nm

Launch

7 March 2009

End

30 October 2018