Yellow hypergiant Very luminous, massive evolved stars with spectral types A–K; extremely rare, highly unstable, and prone to heavy mass loss as they cross late stages of stellar evolution.
Yinghuo-1 — China’s first planned Mars spacecraft Yinghuo-1 Yinghuo-1 was China’s first planned interplanetary probe, launched with Russia’s Phobos‑Grunt in November 2011 to study Mars. It failed to leave Earth orbit and reentered in Januar…
Ymir — a small irregular moon of Saturn Ymir (moon) Ymir (Saturn XIX) is a small, retrograde irregular satellite discovered in 2000. Named for a figure in Norse myth, it orbits Saturn at ~23.2 million km with a high inclination and…
Yohkoh — Japanese Solar X‑ray Observatory Yohkoh Yohkoh (meaning “sunbeam”) was a Japanese solar observatory satellite launched in 1991 to study the Sun in X-rays and high-energy wavelengths; it produced a long record of solar-fl…
Yutu (Jade Rabbit) lunar rover Yutu (rover) Yutu (Jade Rabbit) is China’s six-wheeled lunar rover deployed by Chang’e‑3 in December 2013, carrying cameras, spectrometers and a ground-penetrating radar to study the Moon’s sur…
Zenith (astronomy and everyday usage) Zenith The zenith is the direction or point in the sky directly above a particular location, opposite the nadir and defined by the local direction of gravity; used in navigation, astronom…
Zodiac: the twelve-sign system of constellations and cultural meanings Zodiac Overview of the Zodiac: its constellations, twelve signs, origins, cultural uses in astrology and astronomy, and notable distinctions between myth, symbolism, and science.
Zone of Avoidance Region of the sky obscured by the Milky Way where dust and stars hide extragalactic objects; modern infrared and radio surveys reduce the gap and reveal hidden large-scale structur…
