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The timeline of discovery of Solar System planets and their natural satellites charts the progress of the discovery of new bodies over history. Each object is listed in chronological order of its discovery (multiple dates occur when the moments of imaging, observation, and publication differ), identified through its various designations (including temporary and permanent schemes), and the ...
Evidence for such clouds was observed during the oppositions of 1892 and 1907. In 1909, Antoniadi noted that the presence of yellow clouds was associated with the obscuration of albedo features. He discovered that Mars appeared more yellow during oppositions when the planet was closest to the Sun and was receiving more energy.
This uncrewed mission flew by Pluto in July 2015. The mission was extended to observe a number of other Kuiper belt objects, including a close flyby of 486958 Arrokoth on New Year's Day, 2019. [68] As of 2011, American scientists are concerned that exploration beyond the Asteroid Belt will hampered by a shortage of Plutonium-238. [needs update]
Later in the same year, Norman Lockyer observed the same line in the solar spectrum, and concluded that it was caused by an element in the Sun unknown on Earth. This element is helium, which currently comprises 23.8% of the mass in the solar photosphere. [150] 1877 – Asaph Hall discovers Mars's moons Deimos and Phobos. [151]
Consequently, Venus transits only occur when an inferior conjunction takes place during some days of June or December, when the orbits of Venus and Earth cross a straight line with the Sun. [189] This results in Venus transiting above Earth in a sequence currently of 8 years, 105.5 years, 8 years and 121.5 years, forming cycles of 243 years.
The solar day (or sol) on Mars is only slightly longer than an Earth day: 24 hours, 39 minutes, and 35.244 seconds. [185] A Martian year is equal to 1.8809 Earth years, or 1 year, 320 days, and 18.2 hours. [ 2 ]
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The Sumerians named the planet after the goddess Inanna, who was known as Ishtar by the later Akkadians and Babylonians. [1] [2] [3] One of the oldest surviving astronomical documents, from the Babylonian library of Ashurbanipal around 1600 BC, is a 21-year record of the appearances of Venus. [4]