Solar Eclipse

Partial and annular eclipses

Viewing the Sun during partial and annular eclipses (and during total eclipses outside the brief period of totality) requires special eye protection, or indirect viewing methods, if eye damage is to be avoided. The Sun's disk can be viewed using appropriate filtration to block the harmful part of the Sun's radiation. Sunglasses do not make viewing the sun safe. Only properly designed and certified solar filters should be used for direct viewing of the Sun's disk. Especially, self-made filters using common objects such as a floppy disk removed from its case, a Compact Disc, a black colour slide film, etc. must be avoided despite what may have been said in the media.

The safest way to view the Sun's disk is by indirect projection. This can be done by projecting an image of the disk onto a white piece of paper or card using a pair of binoculars (with one of the lenses covered), a telescope, or another piece of cardboard with a small hole in it (about 1 mm diameter), often called a pinhole camera. The projected image of the Sun can then be safely viewed; this technique can be used to observe sunspots, as well as eclipses. Care must be taken, however, to ensure that no one looks through the projector (telescope, pinhole, etc.) directly. Viewing the Sun's disk on a video display screen (provided by a video camera or digital camera) is safe, although the camera itself may be damaged by direct exposure to the Sun. The optical viewfinders provided with some video and digital cameras are not safe. Securely mounting #14 welder's glass in front of the lens and viewfinder protects the equipment and makes viewing possible. Professional workmanship is essential because of the dire consequences any gaps or detaching mountings will have. In the partial eclipse path one will not be able to see the corona or nearly complete darkening of the sky, yet, depending on how much of the sun's disk is obscured, some darkening may be noticeable. If two-thirds or more of the sun is obscured, then an effect can be observed by which the daylight appears to be dim, as if the sky were overcast, yet objects still cast sharp shadows.

Solar Eclipse

Geometry of a Total Solar Eclipse

As seen from the Earth, a solar eclipse occurs when the Moon passes between the Sun and the Earth, and the Moon fully or partially covers the Sun as viewed from some location on Earth. This can only happen during a new moon, when the Sun and Moon are in conjunction as seen from Earth. At least two, and up to five, solar eclipses occur each year; no more than two can be total eclipses. Total solar eclipses are nevertheless rare at any particular location because totality exists only along a narrow path traced by the Moon's umbra.

Many people will travel to remote locations to observe a central solar eclipse (see Types below). The solar eclipse of August 11, 1999, in Europe helped to increase public awareness of the phenomenon, which apparently led an unusually large number of journeys made specifically to witness the total solar eclipse of October 3, 2005, and of March 29, 2006.

The last total eclipse was the solar eclipse of July 22, 2009; the next will be the solar eclipse of July 11, 2010. The recent solar eclipse of January 15, 2010, was an annular eclipse (see Types below); the next annular eclipse will occur on solar eclipse of May 20, 2012.

A total solar eclipse is a natural phenomenon. Nevertheless, in ancient times, and in some cultures today, solar eclipses have been attributed to supernatural causes or regarded as bad omens. A total solar eclipse can be frightening to people who are unaware of their astronomical explanation, as the Sun seems to disappear in the middle of the day and the sky darkens in a matter of minutes.

Meteoroid

A meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's (or another body's) atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteor reaches the ground and survives impact, then it is called a meteorite. Many meteors appearing seconds or minutes apart are called a meteor shower. The root word meteor comes from the Greek meteōros, meaning "high in the air".

The current official definition of a meteoroid from the International Astronomical Union is "a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom." The Royal Astronomical Society has proposed a new definition where a meteoroid is between 100 µm and 10 m across. The NEO definition includes larger objects, up to 50 m in diameter, in this category. Very small meteoroids are known as micrometeoroids (see also interplanetary dust).

The composition of meteoroids can be determined as they pass through Earth's atmosphere from their trajectories and the light spectra of the resulting meteor. Their effects on radio signals also give information, especially useful for daytime meteors which are otherwise very difficult to observe. From these trajectory measurements, meteoroids have been found to have many different orbits, some clustering in streams (see Meteor showers) often associated with a parent comet, others apparently sporadic. Debris from meteoroid streams may eventually be scattered into other orbits. The light spectra, combined with trajectory and light curve measurements, have yielded various compositions and densities, ranging from fragile snowball-like objects with density about a quarter that of ice, to nickel-iron rich dense rocks.

Meteoroids travel around the sun in a variety of orbits and at various velocities. The fastest ones move at about 26 miles per second (42 kilometers per second) through space in the vicinity of Earth's orbit. The earth travels at about 18 miles per second (29 kilometers per second). Thus, when meteoroids meet the Earth's atmosphere head-on (which would only occur if the meteor were in a retrograde orbit), the combined speed may reach about 44 miles per second (71 kilometers per second).

Meteoroid, Meteor And Meteorite

Comets

A comet is a relatively small, rocky, and icy mass in the Solar System, usually larger than a meteoroid, that, when it is close enough to the Sun, displays a visible coma (a thin, fuzzy, temporary atmosphere), and sometimes also a tail, both because of the effects of solar radiation and the solar wind upon the nucleus of the comet. Comet nuclei are loose collections of ice, dust, and small rocky particles, ranging from a few hundred meters to tens of kilometers across. Comets have been observed since ancient times and have historically been considered bad omens. The number visible to the naked eye averages to roughly one per year, though many of these are faint and unspectacular. Particularly bright or notable examples are called "Great Comets".

Comets have a wide range of different orbital periods, ranging from just a few years to hundreds of thousands of years. Some rare hyperbolic comets have been found by calculations in celestial mechanics to pass only once through the inner Solar System before being thrown out into interstellar space along hyperbolic trajectories.

Short-period comets have been found to originate in the Kuiper Belt, or its associated scattered disc, which lie beyond the orbit of Neptune. Longer-period comets are thought to have their origins much further away in the Oort Cloud, a cloud of icy bodies at the outer boundaries of the Solar System that were left behind during the condensation of the solar nebula. Long-period comets plunge towards the Sun from the Oort Cloud because of gravitational perturbations caused by either the massive outer planets of the Solar System (Jupiter, Saturn, Uranus, and Neptune), or passing stars.

Comets are distinguished from asteroids by the presence of a coma and/or a tail. However, ancient comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust, and may come to resemble small asteroids (see Extinct comets). Asteroids are thought to have a different origin from comets, having formed in the inner Solar System (inside the orbit of Jupiter) rather than in the outer Solar System, but recent findings have somewhat blurred the distinction between asteroids and comets (see centaurs and asteroid terminology).

As of May 2009^[update] there are a reported 3,648 known comets of which about 1,500 are Kreutz Sungrazers and about 400 are short-period. This number is steadily increasing. However, this represents only a tiny fraction of the total potential comet population: the reservoir of comet-like bodies in the outer solar system may number one trillion.



Comet Holmes (17P/Holmes) in 2007 showing blue ion tail on right



The Great Comet of 1882, is a member of the Kreutz group

Comet McNaught (C/2006 P1)

The Solar System

Our solar system consists of an average star we call the Sun, the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. It includes: the satellites of the planets; numerous comets, asteroids, and meteoroids; and the interplanetary medium. The Sun is the richest source of electromagnetic energy (mostly in the form of heat and light) in the solar system. The Sun's nearest known stellar neighbor is a red dwarf star called Proxima Centauri, at a distance of 4.3 light years away. The whole solar system, together with the local stars visible on a clear night, orbits the center of our home galaxy, a spiral disk of 200 billion stars we call the Milky Way. The Milky Way has two small galaxies orbiting it nearby, which are visible from the southern hemisphere. They are called the Large Magellanic Cloud and the Small Magellanic Cloud. The nearest large galaxy is the Andromeda Galaxy. It is a spiral galaxy like the Milky Way but is 4 times as massive and is 2 million light years away. Our galaxy, one of billions of galaxies known, is traveling through intergalactic space.

The planets, most of the satellites of the planets and the asteroids revolve around the Sun in the same direction, in nearly circular orbits. When looking down from above the Sun's north pole, the planets orbit in a counter-clockwise direction. The planets orbit the Sun in or near the same plane, called the ecliptic. Pluto is a special case in that its orbit is the most highly inclined (18 degrees) and the most highly elliptical of all the planets. Because of this, for part of its orbit, Pluto is closer to the Sun than is Neptune. The axis of rotation for most of the planets is nearly perpendicular to the ecliptic. The exceptions are Uranus and Pluto, which are tipped on their sides.

Composition Of The Solar System

The Sun contains 99.85% of all the matter in the Solar System. The planets, which condensed out of the same disk of material that formed the Sun, contain only 0.135% of the mass of the solar system. Jupiter contains more than twice the matter of all the other planets combined. Satellites of the planets, comets, asteroids, meteoroids, and the interplanetary medium constitute the remaining 0.015%. The following table is a list of the mass distribution within our Solar System.

• Sun: 99.85%
• Planets: 0.135%
• Comets: 0.01% ?
• Satellites: 0.00005%
• Minor Planets: 0.0000002% ?
• Meteoroids: 0.0000001% ?
• Interplanetary Medium: 0.0000001% ?

Interplanetary Space

Nearly all the solar system by volume appears to be an empty void. Far from being nothingness, this vacuum of "space" comprises the interplanetary medium. It includes various forms of energy and at least two material components: interplanetary dust and interplanetary gas. Interplanetary dust consists of microscopic solid particles. Interplanetary gas is a tenuous flow of gas and charged particles, mostly protons and electrons -- plasma -- which stream from the Sun, called the solar wind.

The solar wind can be measured by spacecraft, and it has a large effect on comet tails. It also has a measurable effect on the motion of spacecraft. The speed of the solar wind is about 400 kilometers (250 miles) per second in the vicinity of Earth's orbit. The point at which the solar wind meets the interstellar medium, which is the "solar" wind from other stars, is called the heliopause. It is a boundary theorized to be roughly circular or teardrop-shaped, marking the edge of the Sun's influence perhaps 100 AU from the Sun. The space within the boundary of the heliopause, containing the Sun and solar system, is referred to as the heliosphere.

The solar magnetic field extends outward into interplanetary space; it can be measured on Earth and by spacecraft. The solar magnetic field is the dominating magnetic field throughout the interplanetary regions of the solar system, except in the immediate environment of planets which have their own magnetic fields.

The Terrestrial Planets

The terrestrial planets are the four innermost planets in the solar system, Mercury, Venus, Earth and Mars. They are called terrestrial because they have a compact, rocky surface like the Earth's. The planets, Venus, Earth, and Mars have significant atmospheres while Mercury has almost none. The following diagram shows the approximate distance of the terrestrial planets to the Sun.

The Jovian Planets

Jupiter, Saturn, Uranus, and Neptune are known as the Jovian (Jupiter-like) planets, because they are all gigantic compared with Earth, and they have a gaseous nature like Jupiter's. The Jovian planets are also referred to as the gas giants, although some or all of them might have small solid cores. The following diagram shows the approximate distance of the Jovian planets to the Sun.

Solar System Animation

• Formation of the Solar System.

Views of the Solar System

Our Milkyway Galaxy
This image of our galaxy, the Milky Way, was taken with NASA's Cosmic Background Explorer's (COBE) Diffuse Infrared Background Experiment (DIRBE). This never-before-seen view shows the Milky Way from an edge-on perspective with the galactic north pole at the top, the south pole at the bottom and the galactic center at the center. The picture combines images obtained at several near-infrared wavelengths. Stars within our galaxy are the dominant source of light at these wavelengths. Even though our solar system is part of the Milky Way, the view looks distant because most of the light comes from the population of stars that are closer to the galactic center than our own Sun. (Courtesy NASA)
Our Milky Way Gets a Makeover
Like early explorers mapping the continents of our globe, astronomers are busy charting the spiral structure of our galaxy, the Milky Way. Using infrared images from NASA's Spitzer Space Telescope, scientists have discovered that the Milky Way's elegant spiral structure is dominated by just two arms wrapping off the ends of a central bar of stars. Previously, our galaxy was thought to possess four major arms.

This artist's concept illustrates the new view of the Milky Way, along with other findings presented at the 212th American Astronomical Society meeting in St. Louis, Mo. The galaxy's two major arms (Scutum-Centaurus and Perseus) can be seen attached to the ends of a thick central bar, while the two now-demoted minor arms (Norma and Sagittarius) are less distinct and located between the major arms. The major arms consist of the highest densities of both young and old stars; the minor arms are primarily filled with gas and pockets of star-forming activity.

The artist's concept also includes a new spiral arm, called the "Far-3 kiloparsec arm," discovered via a radio-telescope survey of gas in the Milky Way. This arm is shorter than the two major arms and lies along the bar of the galaxy.

Our sun lies near a small, partial arm called the Orion Arm, or Orion Spur, located between the Sagittarius and Perseus arms. (Courtesy NASA/JPL-Caltech)
Spiral Galaxy, NGC 4414
The majestic galaxy, NGC 4414, is located 60 million light-years away. Like the Milky Way, NGC 4414 is a giant spiral-shaped disk of stars, with a bulbous central hub of older yellow and red stars. The outer spiral arms are considerably bluer due to ongoing formation of young, blue stars, the brightest of which can be seen individually at the high resolution provided by the Hubble camera. The arms are also very rich in clouds of interstellar dust, seen as dark patches and streaks silhouetted against the starlight. (Courtesy NASA/STSCI)
Obliquity of the Eight Planets
This illustration shows the obliquity of the eight planets. Obliquity is the angle between a planet's equatorial plane and its orbital plane. By International Astronomical Union (IAU) convention, a planet's north pole lies above the ecliptic plane. By this convention, Venus, Uranus, and Pluto have a retrograde rotation, or a rotation that is in the opposite direction from the other planets. (Copyright 2008 by Calvin J. Hamilton)
The Solar System
During the past three decades a myriad of space explorers have escaped the confines of planet Earth and have set out to discover our planetary neighbors. This picture shows the Sun and all nine planets of the solar system as seen by the space explorers. Starting at the top-left corner is the Sun followed by the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. (Copyright 1998 by Calvin J. Hamilton)
Sun and Planets
This image shows the Sun and nine planets approximately to scale. The order of these bodies are: Sun, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. (Copyright Calvin J. Hamilton)
Jovian Planets
This image shows the Jovian planets Jupiter, Saturn, Uranus and Neptune approximately to scale. The Jovian planets are named because of their gigantic Jupiter-like appearance. (Copyright Calvin J. Hamilton)
The Largest Moons and Smallest Planets
This image shows the relative sizes of the largest moons and the smallest planets in the solarsystem. The largest satellites pictured in this image are: Ganymede (5262 km), Titan (5150 km), Callisto (4806 km), Io (3642 km), the Moon (3476 km), Europa (3138 km), Triton (2706 km), and Titania (1580 km). Both Ganymede and Titan are larger than planet Mercury followed by Io, the Moon, Europa, and Triton which are larger than the planet Pluto. (Copyright Calvin J. Hamilton)
Diagram of Portrait Frames
On February 14, 1990, the cameras of Voyager 1 pointed back toward the Sun and took a series of pictures of the Sun and the planets, making the first ever "portrait" of our solar system as seen from the outside. This image is a diagram of how the frames for the solar system portrait were taken. (Courtesy NASA/JPL)
All Frames from the Family Portrait
This image shows the series of pictures of the Sun and the planets taken on February 14, 1990, for the solar system family portrait as seen from the outside. In the course of taking this mosaic consisting of a total of 60 frames, Voyager 1 made several images of the inner solar system from a distance of approximately 6.4 billion kilometers (4 billion miles) and about 32° above the ecliptic plane. Thirty-nine wide angle frames link together six of the planets of our solar system in this mosaic. Outermost Neptune is 30 times further from the Sun than Earth. Our Sun is seen as the bright object in the center of the circle of frames. The insets show the planets magnified many times. (Courtesy NASA/JPL)
Portrait of the Solar System
These six narrow-angle color images were made from the first ever "portrait" of the solar system taken by Voyager 1, which was more than 6.4 billion kilometers (4 billion miles) from Earth and about 32° above the ecliptic. Mercury is too close to the Sun to be seen. Mars was not detectable by the Voyager cameras due to scattered sunlight in the optics, and Pluto was not included in the mosaic because of its small size and distance from the Sun. These blown-up images, left to right and top to bottom are Venus, Earth, Jupiter, Saturn, Uranus, and Neptune. (Courtesy NASA/JPL)

Sun and Planet Summary

The following table lists statistical information for the Sun and planets:

	Distance (AU)	Radius (Earth's)	Mass (Earth's)	Rotation (Earth's)	# Moons	Orbital Inclination	Orbital Eccentricity	Obliquity	Density (g/cm3)
Sun	0	109	332,800	25-36*	9	---	---	---	1.410
Mercury	0.39	0.38	0.05	58.8	0	7	0.2056	0.1°	5.43
Venus	0.72	0.95	0.89	244	0	3.394	0.0068	177.4°	5.25
Earth	1.0	1.00	1.00	1.00	1	0.000	0.0167	23.45°	5.52
Mars	1.5	0.53	0.11	1.029	2	1.850	0.0934	25.19°	3.95
Jupiter	5.2	11	318	0.411	16	1.308	0.0483	3.12°	1.33
Saturn	9.5	9	95	0.428	18	2.488	0.0560	26.73°	0.69
Uranus	19.2	4	17	0.748	15	0.774	0.0461	97.86°	1.29
Neptune	30.1	4	17	0.802	8	1.774	0.0097	29.56°	1.64
Pluto	39.5	0.18	0.002	0.267	1	17.15	0.2482	119.6°	2.03

* The Sun's period of rotation at the surface varies from approximately 25 days at the equator to 36 days at the poles. Deep down, below the convective zone, everything appears to rotate with a period of 27 days.

Extinct Species

Sophora Toromiro

Cosmos Atrosanguineus

Saint Helena Olive

Cooksonia

seventymph

pvorchirds