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XRISM Resolve
Resolve is the X-ray microcalorimeter spectrometer aboard XRISM, an X-ray astronomy satellite developed by JAXA and NASA and launched from Japan in 2023; it measures each photon's energy as heat at 50 milli-Kelvin.
Yebes Observatory
Yebes Observatory (Observatorio de Yebes) is a Spanish radio astronomy and geodesy facility near Madrid, home to a 40 m radio telescope, inaugurated in 2005.
Yohkoh
Yohkoh (ようこう, "Sunbeam"), also known as SOLAR-A, was a Japanese X-ray solar observation satellite launched in 1991 by ISAS with US and UK cooperation, observing solar flares until 2001.
Z 184-50
Z 184-50, also known as Markarian 421, is a bright nearby blazar in Ursa Major that the Whipple Observatory detected in 1992 as the first TeV blazar.
Z 225-7
Z 225-7 is a catalog designation of Markarian 501, a nearby blazar in Hercules and one of the brightest very-high-energy gamma-ray sources in the sky.
Zenith
The zenith is the point on the celestial sphere directly above a given observer, the direction opposite the nadir; a star there has an altitude of 90 degrees.
ZEPLIN
ZEPLIN was a series of dark matter search experiments using liquid xenon detectors at the Boulby Underground Laboratory in northeast England, running from the late 1990s through 2012.
Zhang Heng
Zhang Heng (張衡, Pingzi, 78–139 CE) was a Han-dynasty polymath from Nanyang who invented the first seismoscope, built a water-powered armillary sphere, and wrote the Lingxian.
Zone of avoidance
The Zone of Avoidance (ZoA) is the band of sky along the Milky Way's plane where dust blocks the light of background galaxies, covering about 20% of the sky.
Zwicky Transient Facility
The Zwicky Transient Facility (ZTF) is an optical sky survey at Palomar Observatory in California that has scanned the northern sky for changing objects, especially supernovae, since 2018.