Posts Tagged ‘solar system’

Ashen Light

When the plant Venus appears as a crescent, the night side sometimes appears dimly luminous. This is the Ashen light, also known as the Ashen Glow.

It is one of the many unexplained mysteries of the Solar system. It was first noted by an Italian astronomer Giovanni Battista Riccioli way back in 1643 and has been seen by many astronomers since – including Big Bill (Herschel). professionals operating the Keck telescope and of course the late great Patrick Moore. No photographic images exist of the Ashen Light and many professional astronomers have never seen this phenomenon, however, it is accepted as being a genuine thing.

Various theories have been proposed to explain the Ashen Light including atmospheric ionisation, lightning and Venusian inhabitants either carrying out slash and burn agriculture or celebrating the crowning of a new ruler!

This article by Jenny Winder sums it all up nicely


The physical study of the planet Mars.

But why Areography? Mars has always been associated with the god of war. The Babylonians were keen astronomers and names Mars Negral. Negral is the Babylonian god of war. This appears to have carried over to other civilisations but it was the Roman name for the god of war that has ‘stuck’. Ares was the Greek god of war, the son of Zeuss and Hera. Ares is the root of this word … it does have a better ring to it than marsography!

No one can say for certain why each planet was names for a particular god, some say that it is because of the red colour of the planet in the night sky that reminded the ancients of blood and therefore battles. I guess it is also possible that one of the city states of the middle east was attacked when Mars appeared in the sky. The winners of the battle may have then decided that it was the god of war looking down on their efforts and helping? Who knows?

The first areographer of note was the Italian, Giovanni Schiaparelli, who started the myth of the canals of mars. The word he used to describe the features he had seen was ‘canali’ which properly translates as ‘channels’. That was in 1877 and people have been seeing all sorts of evidence of a former civilisation on Mars ever since!

As a result, there are many fiction and factual books concerning Mars …


When something is orbiting the Sun, this is the point of the orbit that is furthest from the Sun. It applies to anything in solar orbit – planet, comet, minor planet, dust particle …

For the Earth, aphelion is around July 4th, when the Northern Hemisphere is in summer.  The word aphelion derives from the Greek words, apo meaning away, off, apart and Helios (the Greek god of the sun).

The reason why the this occurs is because orbits are elliptical and not circular. Kepler realised this and published the information in 1609. An ellipse has two foci which I suppose can be regarded as the equivalent of the centre of a circle and are used to construct the ellipse. In terms of an orbit, the Sun sits at one of the foci therefore as a body orbits the Sun it will have a varying distance.

Illustration of aphelion and perihelion

Illustration of aphelion and perihelion

There is a further explanation and animation at


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


Albedo of an astronomical body

A measure of how reflective a body is. Albedo is expressed as a percentage, the higher the percentage, the higher the albedo and therefore the more reflective the object is.

On the face of it, albedo is a straightforward thing, however, the albedo of a planet varies from place to place. Dark surfaces absorb more light than light surfaces. Rough surfaces scatter light in all directions and therfore reflect less back to the observer. Thus when talking about the albedo of an astronomical body, one generally means the average albedo.

Cloudy planets like the gas giants and Venus have high albedos because clods are good reflectors whilst the rocky planets have lower albedos.

The light reaching your eye from an object is reduced thr further it has to travel so the albedo at the edge of a planet is less than at the centre, assuming the same surface composition. Accurate measurements of albedo need to take this into account and so there are two types of albedo, spherical and geometrical. The latter assumes the planet, asteroid, moon or whatever is a uniform sphere whilst the latter compares the reflecting power of the object with that of a flat white disc of the same diameter and distance as the object.

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