MIRA 24
March 1989



JUPITER

Observer Revd. Tim Gouldstone


Left
Date         1988 November 6th.
Time         20h 55m to 21h 10m U.T.
Instrument 216mm Reflector Mag. x216
Conditions  Moderate East wind.

SPR dark N. margin.
STB darker p. than f.
STr Z linear feature from RS and dark band near f. margin.
SEBs very dist. f. RS.
SEBn dark N. margin w. irregular.
EZ festoons from NEBn.
NEBs darker p. than f. and very irregular near p. limb.
Lighter area in centre NEB near meridian.
NEBn very dark on N. margin, festoons into NTr Z.
NTB appears lighter in central part on f. side
CM1 = 342°   CM2 = 72°


Right
Date          1988 November 10th.
Time          20h to 20h 15m U.T.
Instrument 216mm Reflector Mag. x155 and 216
Conditions  Moderate to good.

SPR dark N. margin.
STB very broad, with dark features.
STr Z has dark band p. meridian.
Sebn dark and very irregular S. margin.
SEBs uniform.
EZ darker feature on p, limb.festoons from NEBs.
NEBs dark and very irregular west festoons into EZ.
NEBn dark margin but reasonably straight.
NTr Z festoons from NTB.
NTB irregular and active.
NPR darker f. than p.
CM1 = 203°    CM2 = 263°





Mare Humorum


Drawn by I. Clarke


Mare Humorum (SEA OF MOISTURE) is at 23°S, 58°W
Date 17 / 1 / 1989,  20.45 to 21.15 UT
Moon 10 days old
The Mare was only half lit by the rising sun, showing a lot of ridges on its floor.  The crater at the top is Doppelmayer (68km) at the bottom with just its east wall lit is Gassendi (89km).  The walls of both craters were very bright, Gassendi is prone to TLP.





EYE SEE
By B. Merrikin

Many observers are aware of the techniques of "Averted. Vision" when attempting to glimpse faint objects such as double stars or to distinguish detail in such things as galaxies and nebula.  In fact, some objects can only be seen using this technique but a great deal of satisfaction can be had in just tracking down these objects despite the difficulty in discerning any detail.
The reason that makes Averted Vision useful in these circumstances can easily be explained.  The image of an object is focused on the retina of the eye by the cornea, the aqueous humour, the crystalline lens and the vitreous humour.  These combine to give a focal length typically of the order of 15mm for an average adult.
The retina itself is made up of two types of light sensitive nerve endings, namely cones and rods (so named because of their shape).  The cones are responsible for distinguishing colour and bright illumination and are predominant in the central area of the retina.  In fact, they are the only light sensitive elements in the fovea centralis where we have our highest resolving power.  The rods, on the other hand, are responsible for distinguishing movement and objects at low illumination but cannot distinguish colour.
The rods predominate the periphery of the retina and occur in their maximum number about 20  from the centre of the retina.  There are approximately 120 million rods and six million cones contained within the retina, which makes the eye still far more sensitive than the latest electronic devices in use today.
The eye produces rhodopsin (or visual purple) in low light situations which is absorbed by the rods. This substance disappears when exposed to light.  This is one reason why the eye takes time to adjust to the dark and serious observations of faint objects can only begin when the eye has become "dark adapted", which should take at least half of one hour.  Also this substance responds to only 20 per cent of the incoming light, an amount which itself is reduced by 50 per cent due to absorption by the elements of the eye.
Therefore, by diverting the eyes attention away from the intended object to an angle of 20° - 50° from the centre, fainter illuminations can be detected.  Images up to 2.5 magnitudes fainter can be detected using this technique, but this is dependant upon other factors such as age.

In future articles I hope to explain other useful observational techniques and explain some faults which can exist in this most complex of optical instruments.




A Series of Observations of Mars
by the Revd. T.M. Gouldstone
from St. Keverne in Cornwall.  Part One

a
Date       1988 Sept. 11 / 12
Time       OOh 15m U.T.
Instrument 216mm Reflector Mag. x155 and 216
Conditions Seeing good.

Notes
C.M. 12°
Margarifiter and Maridiani darker than other areas.


b
Date       1988 Sept. 15th.
Time       22h to 22h 10m U.T.
Instrument 216mm Reflector Mag. x155 and 216
Conditions Good

Notes
C.M. 305°
Dark area to the N. of Sabaeus
Syrtis Major darker f. side Libya/T
Libya/Tyrrhenum dark.
Dark linear area p. Syrtis Major (A)


c
Date       1988 Sept. 19th.
Time       21 h 45m to 21h 55m U.T.
Instrument 216 Reflector Mag. x155 and 216
Conditions Seeing fair to good, slight mist.

Notes
C.M. 267°
Cimmerium area dark, also p. side of Hesperia.
Darker area 'B'
(Interesting to compare this observation to my own as I observed Mars during the same time as Tim — refer to Mira 23, December 1988, page 4, second illustration down, as I feel they compare favourable well.  However the area marked 'B' in the above observation was strangely not seen by me Ed. V.C.)

d
Date       1988 Oct. 2nd.
Time       20h 5m to 20h 15m U.T.
Instrument 216mm Reflector Mag. x216
Conditions Seeing poor.

Notes
C.M. 126°
Sirenum consp., as Phaetonthis and area believed to be Claritas Fossa.
Solis Planum dark area.
Sirenium darkest feature on the disk.
Slight shading as indicated in N. hem.


e
Date       1988 Oct. 19th.
Time       20h to 20h 15m U.T.
Instrument 216mm Reflector Mag. not stated.
Conditions not stated.

Notes
C.M. 338°
Syrtis Major on p. side, remainder of features hard to identify as shown.


f
Date       1988 Nov. 2nd.
Time       20h 55m to 21h 10m U.T.
Instrument 216mm Reflector Mag. not stated.
Conditions not stated.

Notes
C.M. 231°
Cimmerium and Tyrrhenum and dk. area on the p. side (Chronium ?) near S. polar cap.
No features visible in N. hem.



g
Date       1988 Nov.6th.
Time       20h to 20h 15m U.T.
Instrument 216mm Reflector Mag. not stated
Conditions Moderate seeing.

Notes
C.M.172°
Structure of detail hard to see, receeding planet.
Very faint feature in N. hemisphere in area of Trivium Charontis
Sirenium and Cimmerium conspicuous.
Darker, fairly uniform area N. of S. pole separated by lighter linear area from rest of features.


h
Date       1988 Nov. 10th.
Time       19h 5m to 19h 20m U.T.
Instrument 216mm Reflector Mag. x216
Conditions Moderate seeing after rain and W. wind.

Notes
C.M.121°
Sirenium consp. and Claritas Fossa.
Darker areas S. of Phaetonthis boardering S. Polar Cap.
W. limb appears bright. Extensive faint area in N . hemisphere, best seen with aid of orange filter.





Subjects of Astronomical Interest

It's recently come to the attention of astronomers who have calculated past positions of the planet Neptune, that Galileo first saw and recorded Neptune 234 years before it was positively identified by Galle and D'Arrest in 1846.
Galileo recorded, just by chance in December 1612 and January 1613 a faint point of light thinking that it was just another fixed star, within the telescopic field of view, whilst studying the various movements of Jupiter's four moons.
Further research has revealed other observers, who like Galileo have mistook Neptune as a fixed star the observers are along with dates.
Lalande on the 8th. and 10th. May 1795, Lamond on the 25th. October 1845.
Similarly, Pluto had been photograph at the Mount Wilson Observatory in 1919, followed by Yerkes in 1921, 1927 and again in 1927 at the Royal Observatory Uccle in Belgium, before it's real identity became established by Tombaugh in 1930.

I would be most pleased if any member could kindly contribute something of the lines above for future issues of MIRA, it could be either astronomical or spaceflight related subjects.
Thanks Ed V.C.






Mersenius

Drawn by Vaughan Cooper


Date         1988 Jan. 30th
Time         20h 15m to 21h 00m
Conditions  A little unsteady
Instrument  6" f/10 Reflector  x240
Co-long      52.75 to 53.10


A fine 41 mile diameter crater with a convex floor 3,000 feet below the region on it's western boarder. The inner southern wall displays subtle detail along with what appears to be two overlapping craters.

Note the thin shadow line following the internal western wall running in a north to south direction, this could be part of the inner western wall detail or perhaps a cleft.