Earth

Question

This piglix contains articles or sub-piglix about Earth

Answer 1

Near-Earth supernova

A near-Earth supernova is an explosion resulting from the death of a star that occurs close enough to the Earth (roughly less than 10 to 300 parsecs (30 to 1000 light-years) away) to have noticeable effects on its biosphere.

On average, a supernova explosion occurs within 10 parsecs (33 light-years) of the Earth every 240 million years.Gamma rays are responsible for most of the adverse effects a supernova can have on a living terrestrial planet. In Earth's case, gamma rays induce a chemical reaction in the upper atmosphere, converting molecular nitrogen into nitrogen oxides, depleting the ozone layer enough to expose the surface to harmful solar and cosmic radiation (mainly ultra-violet). Phytoplankton and reef communities would be particularly affected, which could severely deplete the base of the marine food chain.

Speculation as to the effects of a nearby supernova on Earth often focuses on large stars as Type II supernova candidates. Several prominent stars within a few hundred light years of the Sun are candidates for becoming supernovae in as little as a millennium. Although they would be spectacular to look at, were these "predictable" supernovae to occur, they are thought to have little potential to affect Earth.

It is estimated that a Type II supernova closer than eight parsecs (26 light-years) would destroy more than half of the Earth's ozone layer. Such estimates are based on atmospheric modeling and the measured radiation flux from SN 1987A, a Type II supernova in the Large Magellanic Cloud. Estimates of the rate of supernova occurrence within 10 parsecs of the Earth vary from 0.05–0.5 per Ga to 10 per Ga. Several studies assume that supernovae are concentrated in the spiral arms of the galaxy, and that supernova explosions near the Sun usually occur during the ~10 million years that the Sun takes to pass through one of these regions. Examples of relatively near supernovae are the Vela Supernova Remnant (~800 ly, ~12,000 years ago) and Geminga (~550 ly, ~300,000 years ago).

...

Wikipedia

Answer 2

Earth symbol

A variety of symbols or iconographic conventions are used to represent , either in the sense of planet Earth, or the inhabited world. Representations of the globe of Earth, either with an indication of the shape of the continents or with a representation of meridians and parallels remains a common pictographic convention to express the notion of "worldwide, global". The modern astronomical symbol for Earth as a planet uses either a stylized globus cruciger (♁) or a circle with a cross (representing the equator and one meridian; (

...

Wikipedia

Answer 3

Transit of Earth from Mars

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. During a transit, Earth would be visible from Mars as a small black disc moving across the face of the Sun. They occur every 26, 79 and 100 years, and every 1,000 years or so there is an extra 53rd-year transit.

Transits of Earth from Mars usually occur in pairs, with one following the other after 79 years; rarely, there are three in the series. The transits also follow a 284-year cycle, occurring at intervals of 100.5, 79, 25.5, and 79 years; a transit falling on a particular date is usually followed by another transit 284 years later. Transits occurring when Mars is at its ascending node are in May, those at descending node happen in November. This cycle corresponds fairly closely to 151 Mars orbits, 284 Earth orbits, and 133 synodic periods, and is analogous to the cycle of transits of Venus from Earth, which follow a cycle of 243 years (121.5, 8, 105.5, 8). There are currently four such active series, containing from 8 to 25 transits. A new one is set to begin in 2394. The last series ending was in 1211.

No one has ever seen a transit of Earth from Mars, but the next transit will take place on November 10, 2084. The last such transit took place on May 11, 1984.

During the event, the Moon could almost always also be seen in transit, although due to the distance between Earth and Moon, sometimes one body completes the transit before the other begins (this last occurred in the 1800 transit, and will happen again in 2394).

A transit of Earth from Mars corresponds to Mars being perfectly uniformly illuminated at opposition from Earth, its phase being 180.0° without any defect of illumination. During the 1879 event, this permitted Charles Augustus Young to attempt a careful measurement of the oblateness (polar compression) of Mars. He obtained the value 1/219, or 0.0046. This is close to the modern value of 1/154 (many sources will cite somewhat different values, such as 1/193, because even a difference of only a couple of kilometers in the values of Mars' polar and equatorial radii gives a considerably different result).

...

Wikipedia

Answer 4

Windows on Earth

Windows on Earth is a museum exhibit, Web site, and exploration tool, developed by TERC, Inc. (Technical Education Research Centers, an educational non-profit organization), and the Association of Space Explorers, that enables the public to explore an interactive, virtual view of Earth from space. In addition, the tool has been selected by NASA to help astronauts identify targets for photography from the International Space Station (ISS).

The program simulates the view of Earth as seen from a window aboard the ISS, in high-resolution, photographically accurate colors and 3D animations. The views include cloud cover, day and night cycles, night time lights, and other features that help make the exhibit realistic and interactive.

Windows on Earth provides the user a view of Earth from an astronaut's viewpoint, with interactive photorealistic views of Earth as if seen from an altitude of 360 km. The program uses GeoFusion's digital Earth visualization system, which renders accurate views of Earth with terrain, satellite imagery, clouds, and other layers. The system is programmed for user interaction, allowing users to "fly" anywhere they wish to see, and zoom in or out to see details. The system's imagery is derived from Landsat, and features 3D perspective views. Former astronaut Jay Apt assisted with the color-correction of the images, to help get the most realistic colors as seen from space. The program is updated daily to include accurate cloud cover information.

Windows on Earth was created by people from the Center for Earth and Space Science Education (CESSE) at TERC, a not-for profit math and science education company located in Cambridge, MA, in partnership with the Association of Space Explorers, GeoFusion's, and WorldSat International and with funding from the National Science Foundation, Informal Science Education.

Additional partners include the Challenger Learning Center and NASA's Johnson Space Center.

...

Wikipedia

Answer 5

World

The world is the planet Earth and all life upon it, including human civilization. In a philosophical context, the world is the whole of the physical Universe, or an ontological world. In a theological context, the world is the material or the profane sphere, as opposed to the celestial, spiritual, transcendent or sacred. The "end of the world" refers to scenarios of the final end of human history, often in religious contexts.

World history is commonly understood as spanning the major geopolitical developments of about five millennia, from the first civilizations to the present. In terms such as world religion, world language, world government, and world war, world suggests international or intercontinental scope without necessarily implying participation of the entire world.

World population is the sum of all human populations at any time; similarly, world economy is the sum of the economies of all societies or countries, especially in the context of globalization. Terms like world championship, gross world product, world flags imply the sum or combination of all current-day sovereign states.

The English word comes from the Old English weorold (-uld), weorld, worold (-uld, -eld), a compound of wer "man" and eld "age," which thus means roughly "Age of Man." The Old English is a reflex of the Common Germanic *wira-alđiz, also reflected in Old Saxon werold, Old High German weralt, Old Frisian warld and Old Norse verǫld (whence the Icelandic ).

...

Wikipedia