Ashen Light of Venus

While observing Venus on January 9, 1643, Italian astronomer Giovanni Riccioli observed  that the darker side of Venus had a faint greyish glow. He called ‘The ashen light of Venus’.  (He most likely would have named it in Italian which means or resembling ashes or ashen.)

This is how Venus must have appeared to To Giovannii Riccioli, in the evening of Jan 9, 1643.

Venus parameter were
Angular diameter: 38.77″
Magnitude:-4.7
Phase: 0.286
Phase angle:115.3°
Elongation : 41.4°

Later many astronomers reported this phenomenon. Among the notable ones are William Derham Canon of Windsor – reporting the light to be of ‘dull rusty colour’ and Sir William Herschel, (who discovered Uranus) observed the phenomenon on a number of occasions.

In later years many amateur astronomers reported visual observations of ashen light.

But there were others who thought that ashen light is an illusion.  Edward Emerson Barnard, American astronomer ( known for Barnard’s Star) who observed Venus regularly for more than 18 years but never saw ashen light.

On the other hand Sir Patrick Moore reported observation of Ashen Light on number of occasions. But to him the confirmation of existence ashen light for sure came when he observed Venus on 27 May 1980.

There have been a few theories explaining this phenomenon of ashen light. Like thinning of upper atmosphere of Venus at places and the reported glow is that from the hot surface of Venus.  Or multiple lightning in the upper atmosphere.  However, in first case of thinning of atmosphere the hot surface would be visible in infrared, which is not visible to human eyes and the illumination due to lightning would be too faint.

It is suggested oxygen emission in the upper atmosphere. Such emissions were observed by Venera 9 and 10.

Joel S.Levineab of Institute for Space Studies, Goddard Space Flight Center and Geophysical Sciences Laboratory, New York University, in a paper published by him in Planetary and Space Science (Volume 17, Issue 6, June 1969, Pages 1081-1087) observes

“ a general increase in the geomagnetic index coinciding with the occurrence of the Ashen Light at times of inferior conjunction of Venus, which suggests that the Ashen Light is an auroral phenomena due to solar particle bombardment on the dark side of Venus.”  

For his paper he had collected and analysed 129 visual observations of the ashen light.

By the way the most bizarre explanation of ashen light was given by 18th-century German astronomer Franz von Paula Gruithuisen, he suggested that the light is because of fireworks of the Venusians celebrating the ascension of a new emperor.

For more information about these works please visit the following links

Ashen light: the mystery of Venus’s dark-side glow
by Paul Abel, Director of the British Astronomical Association’s Mercury and Venus Section.

The mystery of Venus’ ashen light
by Universe Today

The Ashen Light of Venus: A century of observations
by Richard & Patrick Moore

The Ashen Light of Ashen Light of Ashen Light of Venus: the oldest the oldest unsolved solar system mystery
by William Sheehan, Klaus Brasch, Dale Cruikshank & Richard Baum

What Next

The fact remains Ashen Light has never been photographed. In recent past we have seen many amateur astronomers using modern technology with powerful software have taken some amazing pictures of celetial phenomenon.

In particular I would like to point out the a one by Prabhu S Kutti to took Ramadan crescent moon at 0.2% illumination, captured in the day time (2020-04-23-0744UT).

His set was Esprit 80mm – ZWO 1600mm pro – Red filter stacked 70 frames in Autostakkert, captured from Mleiha, UAE. His picture was just about 5h 19m after the new moon.

I am not sure at this point if this is a record of earliest photograph of Moon.

This is an appeal to amateurs with inclination to do something new. See if you can image the ‘dark side of Venus’. Could there be a scattering of sunlight at the upper atmosphere of Venus.

Observations of Transit of Venus

On 8th of June 2004 I was observing 3rd and 4th contact of transit of Venus from Tehran, Iran.

For detailed account of these observations <click here>

I sketched the event at the 3rd and 4th contact. That is when advancing limb of Venus touched the limb of the Sun and when the tailing limb of Venus just leaving the Sun. The telescope was refactor: 80 mm / f 900, Eye piece 34 mm. It was on equitorial mount.
Angular diameter of Venus was 57.74″

What I observed was as the planet was leaving the sun I could still see some leading part of it, very distinctly, above the solar disk.  And I saw phenomena on number of occasions. 

Giving two examples here:

Third was at 15:32 (local time) and the altitude of the Sun was 55°
Forth was at 15:51 (local time) and the altitude of the Sun was 51°

#9
Saw the advancing limb of Venus outside the solar limb as a white line making an arc – first I thought that it was a trick played by my eyes but then there were two very clear instances of this observations so I sketched this.

#10
15:44:30 –  It is not a half circle any more but kind of two white curves from either sides, kind of trying to meet each other.

For detailed account of these observations <click here>

The CHALLENGE is can someone try imaging Venus as it closes to the Sun.

It would be interesting to see of there is some kind of scattering of sunlight from the ‘darker limb’ of Venus.