Astronomy on Mercury is the sky as viewed from the planet Mercury. Because Mercury only has a thin atmosphere, the sky will be black.
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Astronomy on Mercury is the sky as viewed from the planet Mercury. Because Mercury only has a thin atmosphere, the sky will be black.
Due to the proximity of Mercury to the Sun, Mercury on average receives an energy flux from the Sun that is about 7 times the solar constant, but may reach nearly 11 times at maximum and about 4.5 times at minimum. The Sun will have an angular diameter of 1.733 to 1.142°. From perihelion to aphelion, the size of the Sun increases almost 66%, as does the brightness. This is due to the high eccentricity of Mercury's orbit around the Sun. [1]
Due to tidal locking, three rotations of Mercury, is equal to two revolutions around the Sun. Because of this, the method of plotting the Sun's position at the same time each day would yield only a single point. However, the equation of time can still be calculated for any time of the year, so an analemma can be graphed with this information. The resulting curve is a nearly straight east–west line.
During a Mercurian day, the Sun would be seen rising in the east, move up for a while, stop in the sky, head backwards for a while, and then resume going forwards again. This peculiar movement is due to the orbit of Mercury. If the retrograde motion happens within few hours from sunrise, an observer would see two sunsets and two sunrises, in the same day. The Sun would be seen rising, stopping midway, going back down and setting, rise again, and continue its normal journey. Approximately four (Earth) days before perihelion, the angular speed of Mercury's orbit exactly matches its rotational velocity, so that the Sun's apparent motion stops. At perihelion, Mercury's orbital angular velocity slightly exceeds the rotational velocity, making the Sun appear to go retrograde. Four days after perihelion, the Sun's normal apparent motion resumes. From the moment the top of the Sun can be seen to the moment someone can see a full circle, a sunrise would take almost 6 hours. [2]
Apart from the Sun, Venus would be the brightest celestial body. Venus will be brighter from Mercury, than from Earth. The reason for this is that when Venus is closest to Earth, it is between the Earth and the Sun, so only its night side is seen. Even when Venus is brightest in the Earth's sky, humans see only a narrow crescent. For a Mercurian observer, on the other hand, Venus is closest when it is in opposition to the Sun and is showing its full disk. The apparent magnitude of Venus is as bright as −7.7. [3]
The Earth and the Moon also will be very bright, their apparent magnitudes being about −5 [3] and −1.2, respectively. The maximum apparent distance between the Earth and the Moon is about 15′. Which means that an observer on Mercury could differentiate between Earth and Moon as two separate dots in the sky. The Moon will come closer and closer towards Earth, eventually transiting Earth and moving over to the other side. This movement is because of the revolution of Moon around Earth. It is also possible to observe the Moon undergoing a total lunar eclipse which the MESSENGER spacecraft in orbit around Mercury did for the October 8, 2014 lunar eclipse. [4] [5] All other planets are visible just as they are on Earth, but somewhat less bright at opposition with the difference being most considerable for Mars.
The zodiacal light will be more prominent than it is from Earth. Mercury has a southern pole star, α Pictoris, a magnitude 3.2 star. It is fainter than Earth's Polaris. [6] Omicron Draconis is its north star. [7] Furthermore, the Sun is so bright that it is still impossible to see stars during the daytime, unless the observer is well shielded from sunlight (direct or reflected from the ground).
On February 18, 2011, a portrait of the Solar System was published on the MESSENGER website. The mosaic contained 34 images, acquired by the MDIS instrument during November 2010. All the planets were visible with the exception of Uranus and Neptune, due to their vast distances from the Sun. The MESSENGER "family portrait" was intended to be complementary to the Voyager family portrait, which was acquired from the outer Solar System by Voyager 1 on February 14, 1990. [8]
An eclipse is an astronomical event which occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three celestial objects is known as a syzygy. An eclipse is the result of either an occultation or a transit. A "deep eclipse" is when a small astronomical object is behind a bigger one.
A lunar eclipse is an astronomical event that occurs when the Moon moves into the Earth's shadow, causing the Moon to be darkened. Such an alignment occurs during an eclipse season, approximately every six months, during the full moon phase, when the Moon's orbital plane is closest to the plane of the Earth's orbit.
Mercury is the first planet from the Sun and the smallest in the Solar System. In English, it is named after the ancient Roman god Mercurius (Mercury), god of commerce and communication, and the messenger of the gods. Mercury is classified as a terrestrial planet, with roughly the same surface gravity as Mars. The surface of Mercury is heavily cratered, as a result of countless impact events that have accumulated over billions of years. Its largest crater, Caloris Planitia, has a diameter of 1,550 km (960 mi) and one-third the diameter of the planet. Similarly to the Earth's Moon, Mercury's surface displays an expansive rupes system generated from thrust faults and bright ray systems formed by impact event remnants.
Vulcan was a theorized planet that some pre-20th century astronomers thought existed in an orbit between Mercury and the Sun. Speculation about, and even purported observations of, intermercurial bodies or planets date back to the beginning of the 17th century. The case for their probable existence was bolstered by the support of the French mathematician Urbain Le Verrier, who had predicted the existence of Neptune using disturbances in the orbit of Uranus. By 1859 he had confirmed unexplained peculiarities in Mercury's orbit and predicted that they had to be the result of the gravitational influence of another unknown nearby planet or series of asteroids. A French amateur astronomer's report that he had observed an object passing in front of the Sun that same year led Le Verrier to announce that the long sought after planet, which he gave the name Vulcan, had been discovered at last.
Apparent retrograde motion is the apparent motion of a planet in a direction opposite to that of other bodies within its system, as observed from a particular vantage point. Direct motion or prograde motion is motion in the same direction as other bodies.
In astronomy, a conjunction occurs when two astronomical objects or spacecraft appear to be close to each other in the sky. This means they have either the same right ascension or the same ecliptic longitude, usually as observed from Earth.
In astronomy, a planet's elongation is the angular separation between the Sun and the planet, with Earth as the reference point. The greatest elongation of a given inferior planet occurs when this planet's position, in its orbital path around the Sun, is at tangent to the observer on Earth. Since an inferior planet is well within the area of Earth's orbit around the Sun, observation of its elongation should not pose that much a challenge. When a planet is at its greatest elongation, it appears farthest from the Sun as viewed from Earth, so its apparition is also best at that point.
An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks from view (occults) an object in the background. In this general sense, occultation applies to the visual scene observed from low-flying aircraft when foreground objects obscure distant objects dynamically, as the scene changes over time.
In astronomy, an extraterrestrial sky is a view of outer space from the surface of an astronomical body other than Earth.
Many astronomical phenomena viewed from the planet Mars are the same as or similar to those seen from Earth; but some are quite different. For example, because the atmosphere of Mars does not contain an ozone layer, it is also possible to make UV observations from the surface of Mars.
Solar eclipses on Jupiter occur when any of the natural satellites of Jupiter pass in front of the Sun as seen from the planet Jupiter.
A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby obscuring the view of the Sun from a small part of Earth, totally or partially. Such an alignment occurs approximately every six months, during the eclipse season in its new moon phase, when the Moon's orbital plane is closest to the plane of Earth's orbit. In a total eclipse, the disk of the Sun is fully obscured by the Moon. In partial and annular eclipses, only part of the Sun is obscured. Unlike a lunar eclipse, which may be viewed from anywhere on the night side of Earth, a solar eclipse can only be viewed from a relatively small area of the world. As such, although total solar eclipses occur somewhere on Earth every 18 months on average, they recur at any given place only once every 360 to 410 years.
The Moon orbits Earth in the prograde direction and completes one revolution relative to the Vernal Equinox and the stars in about 27.32 days and one revolution relative to the Sun in about 29.53 days. Earth and the Moon orbit about their barycentre, which lies about 4,670 km (2,900 mi) from Earth's centre, forming a satellite system called the Earth–Moon system. On average, the distance to the Moon is about 385,000 km (239,000 mi) from Earth's centre, which corresponds to about 60 Earth radii or 1.282 light-seconds.
A total lunar eclipse took place on Wednesday 8 October 2014. It is the second of two total lunar eclipses in 2014, and the second in a tetrad. Other eclipses in the tetrad are those of 15 April 2014, 4 April 2015, and 28 September 2015. Occurring only 2.1 days after perigee, the Moon's apparent diameter was larger, 1960.6 arcseconds.
Earth's shadow is the shadow that Earth itself casts through its atmosphere and into outer space, toward the antisolar point. During the twilight period, the shadow's visible fringe – sometimes called the dark segment or twilight wedge – appears as a dark and diffuse band just above the horizon, most distinct when the sky is clear.
In astronomy, a phase curve describes the brightness of a reflecting body as a function of its phase angle. The brightness usually refers the object's absolute magnitude, which, in turn, is its apparent magnitude at a distance of one astronomical unit from the Earth and Sun.
In astronomy, a syzygy is a roughly straight-line configuration of three or more celestial bodies in a gravitational system.
This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outside the atmosphere of Earth. The field of astronomy features an extensive vocabulary and a significant amount of jargon.
In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month.
The following outline is provided as an overview of and topical guide to Venus: