Posts Tagged ‘sun’


This is the plane of the Earth’s orbit projected onto the celestial sphere. Effectively this is the apparent path of the Sun through the sky. Since the main planets of the solar system orbit in more or less the same plane, give or take a few degrees, they are always found close to the ecliptic.


The obscuring of one celestial body by another either by passing directly in front of it or by casting a shadow. Solar eclipses can be total (whole Sun is obscured), partial (part of the Sun is obscured) or annular (a complete ring of sunlight is seen). Lunar eclipses are either total or partial. Quite often, during a total lunar eclipse, the moon is seen to become a coppery colour due to light refracting through the Earth’s atmosphere.

Book: Africa and Madagascar Total Eclipse 2001 & 2002


The corona is a huge envelope of gases that form the outer portion of the Sun. It is seen as faint extensions of the Sun’s outer atmosphere during total eclipses and can be observed using a corongraph, a device that is used to create an artificial total solar eclipse.

The shape of the corona varies with the sunspot cycle. At maximum, it is much more even. At minimum, it is seen to be much more irregular with polar tufts, equatorial streamers and plumes being visible.

It has a temperature of between 1 and 2 million K and naturally at that temperature, is a plasma, for example, iron has been identified but with half of its electrons stripped away. It is indeed a very high energy environment. The corona of the Sun is the origin of the solar wind. An estimated 3 million tonnes of material is ejected from the Sun each second.

This material is experienced as the solar wind with ‘gusts’ of up to several hundred km per sec. The Earth is protected from this bombardment of charged particles by its magnetic field which shunts them into the Van Allen Belts. When these overflow at the poles, they create the aurora borealis and aurora australis.

The solar wind appears to be strongest where it flows from coronal holes. These are areas of lower temperature punched through the corona by the powerful magnetic fields of the Sun.

Copernican System

Although this sounds like some far-flung solar system in a science fiction series, it isn’t! It is a description of how the Solar System is arranged.

The Copernican system is in fact the system proposed (in 1543) by Nicholas Copernicus in which the Sun is the central body, with the Earth and the other bodies moving around it. This model superseded the Ptolemaic system which had persisted for nearly 2000 years. Copernicus’ idea was not new, it had been proposed in about 300 BC by Aristarchus of Samos, a Greek philosopher. Both astronomers have Lunar craters named after them.


This is when a planet has the same longitude as the Sun. A planet can only be observed at conjunction if there is a total eclipse or if it transits the Sun. Unlike the other planets, Mercury and Venus have two types of conjunction, inferior when the planet lies between the Sun and the Earth, superior when it lies on the opposite side of the Sun to the Earth. At inferior conjunction, if the inclination of the orbit of Mercury or Venus coincide with that of the Earth, a transit is observed. These are rare phenomena.

Bailey’s Beads

Brilliant points of light along the edge of the moon disc, just at the start or the end of totality of a total solar eclipse.When caught on camera they are spectacular and can give the diamond ring effect.

They are caused by the irregularities at the edge of the Moon’s disc when seen from Earth. These irregularities are in fact the hills and valleys of the Moon. It is the valleys that allow the light from the Sun to reach the observer when the Moon obscures the Sun.


How to observe eclipses

Astronomical Twilight

The period after sunset when the sun has dropped between 12 and 18 degrees below the horizon.

It is the final phase of twilight, the other two phases being civil twilight (sunset to 6 degrees below the horizon) and nautical twilight (sun is between 6 and 12 degrees below the horizon).

The Analemma

In everyday language, an analemma is the base of a sundial but in astronomical terms it means the angular offset of an astronomical body from its mean position.

When astronomers refer to the analemma, they are normally referring to that of the Sun.

If you take a picture of the Sun at the same time each week, from exactly the same position, on a single frame of film, the figure of eight shape that results is called the analemma. It takes patience and dedication to take a photograph of the analemma.

Wikipedia article

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