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Messier 74 (also known as NGC 628 and Phantom Galaxy) is a large spiral galaxy in the equatorial constellation Pisces. [ a ] It is about 32 million light-years away from Earth. [ 6 ] The galaxy contains two clearly defined spiral arms and is therefore used as an archetypal example of a grand design spiral galaxy . [ 7 ]
In contrast, the Lunar distance (LD or ), or Earth–Moon characteristic distance, is a unit of measure in astronomy. More technically, it is the semi-major axis of the geocentric lunar orbit . The average lunar distance is approximately 385,000 km (239,000 mi), or 1.28 light-seconds ; this is roughly 30 times Earth's diameter .
Around 200 BCE Eratosthenes determines that the radius of the Earth is roughly 6,400 km. [43] Circa 150 BCE Hipparchus uses parallax to determine that the distance to the Moon is roughly 380,000 km. [44] The work of Hipparchus about the Earth-Moon system was so accurate that he could forecast solar and lunar eclipses for the next six centuries.
380 Earth radii (very inaccurate, true=16000 Earth radii) Aristarchus of Samos made a measurement of the distance of the Sun from the Earth in relation to the distance of the Moon from the Earth. The distance to the Moon was described in Earth radii (20, also inaccurate). The diameter of the Earth had been calculated previously.
The distance between the Moon and Earth varies from around 356,400 km (221,500 mi) to 406,700 km (252,700 mi) (apogee), making the Moon's distance and apparent size fluctuate up to 14%. [202] [203] On average the Moon's angular diameter is about 0.52°, roughly the same apparent size as the Sun (see § Eclipses).
The Sun's gravitational effect on the Moon is more than twice that of Earth's on the Moon; consequently, the Moon's trajectory is always convex [26] [27] (as seen when looking Sunward at the entire Sun–Earth–Moon system from a great distance outside Earth–Moon solar orbit), and is nowhere concave (from the same perspective) or looped.
Length of a meridian on Earth (distance between Earth's poles along the surface) [37] 40.075 Mm Length of Earth's equator: 10 8: 100 Mm: 142.984 Mm Diameter of Jupiter: 299.792 Mm Distance traveled by light in vacuum in one second (a light-second, exactly 299,792,458 m by definition of the speed of light) 384.4 Mm Moon's orbital distance from ...
Earth and Moon transiting the Sun in 2084, as seen from Mars. Image created using SpaceEngine Earth and Moon from Mars, as photographed by the Mars Global Surveyor. A transit of Earth across the Sun as seen from Mars takes place when the planet Earth passes directly between the Sun and Mars, obscuring a small part of the Sun's disc for an observer on Mars.