MIRA 21
June 1988


Venus


Date           1988 April 13th.
Time           19.15 U.T.
Instrument  114mm. Catadioptic Reflector Mag. x250
Conditions   Clear sky, some shimmer
Observer     Ivor Clarke



VENUS
Date          1988 May 27th.
Time          20.15. U.T.
Instrument  3in. Refractor Mag. x45
Conditions   Very unsteady
Observer    Vaughan Cooper

Note

The drawing from the 13th. April to the 27th. May are not to scale as Mr. Clarke observed Venus whilst it had an apparent diameter of 26.7 sec. of arc whilst mine, six weeks later, Venus had increased to 51.8 sec. of arc, and so would have to have drawn my drawing a little over half as big again to maintain the correct degree of angular scale.
The above effect is simply due to perspective as Venus is drawing closer to us, hence demonstrating the rapid change in the size of the disk during those six weeks.






The Apparition of Mars 1988
By Vaughan Cooper

Of all recent apparitions of Mars, this coming one will be the most favourable, as Mars will attend the closest position to Earth on 22nd. September, reaching opposition on 28th. September and will have a relatively high declination in the sky of around —2°.
Even during June the diameter of Mars will attend 10.8 seconds of arc, and by using a magnification on your telescope of x240, the image of Mars will nearly be as half as big again as the full Moon appears to the naked eye, so this is a very favourable apparition and must not be missed.
Every opportunity should be made to observe this planet, and the following details may help you what to look for.

Twilight Observations
Provided the planet has a moderate altitude, as it will be around early June, good views may be obtained to some advantage as the diminished glare helps to bring out faint markings which otherwise tends to be swamped out when seen against a dark sky, also a slight mist or haze can be effective in eliminating the glare, so don't let the local atmospheric conditions put you off from observing during this important apparition.

The Polar Cap
The south polar cap will be pointing towards the Earth and will be evaporating, and so visible shrinking during the period up to opposition and may or may not totally disappear.
Usually though, a small remnant remains so look out for cap rifts, bright portions and detached parts.
The regression of the south polar cap may be hindered by Martian cloud activity.
The largest of these observed rifts was first recorded in 1845 and named the Mountains of Mitchel after it's discoverer.  We now know that these 'mountains' are actually low areas where ice is preferentially retained.

Cloud Activity
At irregular and unspecified intervals the surface markings are veiled by clouds in the Martian atmosphere these are of two kinds, yellowish and whitish.
The yellow clouds occasionally cover great areas of the planet and so you may find it difficult to identify certain landmark features. On other occasions cloud may be suspected when any well known dark markings is perhaps whitish in tone or colour or partly invisible, or appears unusually pale whilst neighbouring areas retain their usual intensity and distinctness.
It's possible during late September or early October a major storm will begin, but where will it originate from we can not predict, in previous pre—perihelic years major dust storms have occurred in Hellas Iapigia as in 1986 and before then in 1971, or Solis Casus as in 1973.
If you take the trouble to observe Mars consistently during the coming weeks your observations will make very useful contributions to following any cloud or storm activity and bring right up to date the latest developments on Mars.
The yellow clouds occur low in the Martian atmosphere and are believed to be clouds of dust, the white clouds are less easy to see, they occur high in the Martian atmosphere and believed to be due to solid carbon crystals.
The use of the Wratten range of filters are especially versatile, either a W25 or W29 red, will penetrate the atmosphere to emphasise the dark areas whilst a W44A or W47 blue will high light atmospheric phenomena.

Dust Storms
It's possible during late September or early October a major storm will begin, but where will it originate from we can not predict. In previous pre—perihelic years major dust storms have occurred in Hellas Iapigia as in 1986 and before then in 1971, or Solis Lacus as in 1973.

A list of the names of features which have been known to change in previous apparitions and will require detail observing, see map for positions on the Martian disk.

Hellespontus
Pandorae
Solis Lacus
Phasis
Achillis Fons
Idaeus Fons
Aetheria
Nodus Alcyonius
Gomer Sinus
Hesperia



Mercater projection showing the principal features along the temperate and equatorial region of Mars.
The shaded areas do not represent albedo values.


The size of the Martian disk with dates and magnitude.

June 8   10.8"  -0.4
June 18  11.7"
June 28  12.7"

July 8   13.8"  -1.0
July 18  15.0"
July 28  16.5"

Aug 7    18.0"  -1.7
Aug 17   19.6"
Aug 27   21.3"

Sep 6    22.7"  -2.4
Sep 16   23.5"
Sep 26   23.6"

Observers who are not good draughtsmen or are unable to make drawings, can do useful work by making notes descriptions of the appearance of the features which can be identified with certainty, the visibility of the fainter markings, especially those known to vary, the whitening of specified areas when near the limb and their changed appearance when near the centre of the disk, such notes are generally more useful than inferior sketches.

Drawing scales
2in. in diameter is recommended although a scale of 3mm to the second of arc has been advocated as this avoids over crowding detail at perihelic oppositions.

DO NOT LET THIS APPARITION OF MARS GO BY UNOBSERVED



Pisces

Movement of Mars to be observed with the unaided eye in the constellations of Aquarius and below Pisces.



Additional notes on features mentioned or annotated on the map

Hellas
A vast circular plain of approximately 2,000km. in diameter and often appears very bright and white as seen from Earth, and has been known to be so prominent as to be mistaken for a extra polar cap.
Before space vehicles studied Mars surface Hellas was regarded to be an elevated plateau, upon which white polar deposit persisted when the covering had disappeared from the adjacent areas.
In fact Hellas is a depression basin, the lowest known feature, as it lies 3km. below the mean surface and where the atmospheric pressure is high enough for liquid water to exist.
The western boarder of Hellas is better defined than the eastern boarder as this is probably due to prevailing wind directions on Mars.

Hellespontus
A heavily cratered area to the west of Hellas

Solis Lacus
One of the most variable areas on Mars and since 1877 systematic telescopic observations have noted pronounced changes in shape and intensities of this features. In recent years major changes have occoured in 1971 and 1973.

Nodus Gordil
A lofty volcanic cone of 20km. high and is certainly one of the highest points so far measured on Mars.
Antoniadi noted that it was one of the few features which could still be identified when the planet was still covered with dust.

Syrtis Major
This feature was recorded telescopically by Huygens in the 17th. century and is conspicuous in any moderate telescope.  It has always been regarded as a deep depression but in fact it's a smooth elevated plateau sloping off to either side, but what is surprising from the Mariner photographs, there is nothing to distinguish this feature apart from it's colour.
To the north of Syrtis Major lies Casius nicknamed the Wedge also a albedo feature as is Nilosyrtis undoubtedly one of Lowell's so called canals.
Syrtis Major region has been known to show considerable variation from year to year, particularly the area to the east of Syrtis.

Aetheria
A large area where photographs show relatively few craters.

Acidalium
A large smooth depressed plain, a feature easily seen in moderate telescopes.








Herodotus


Drawn by V. Cooper

Date         1988 Jan 30th
Time         21h 10m to 21h 50m UT
Conditions  A little unsteady
Instrument 6" F/10 Reflector x240
Co-long     53.20 to 53.55


Herodotus

A 21.2 mile diameter formation heavily filled with shadow, due to insufficient advancement of the terminator and as a result the walls not showing any relief details as the sun is shinning directly on them.  Notice the large gap lying towards the N.E. of the crater through which Schroter's valley breaches.
Herodotus lies at the southwestern edge of a large rhomboidal plateau, known as the Aristarchus uplift.  This very unusual region is rich in craters rilles, domes and mountains.  The uplift has been seen to have a most pronounced coloration of a dark olive green hue and is supposed to be easily detectable soon after sunrise, but not noticed during the course of my observation.

Schroter's Valley

Only part of this sinuous valley recorded as it runs north then turns north west well below Herodotus, but what was recorded reasonable well was the tadpole type feature I've drawn called the Cobra Head, which is the widest part of the valley about 30 miles north of Herodotus.
The valley was first discovered by Huygens in 1686 but a little over a hundred years had to elapse before Schroter first examined it on the 7th October 1787.
There have been many conjectures about the origins of Schroter's Valley as it may be a graben (a sunken area bounded by faults) but it is very sinuous for this or it could have been a drainage; canal from Herodotus, whatever, it is a remarkable feature and even today it still pays careful study as in this area strange red glows were observed in November 1963 by J. Greenacre and E. Barr at the Lowell observatory.
Other features worth examining for the future are one of the bright rays from Aristarchus crossing the southern part of the floor of Herodotus, less easily seen is the one mile diameter craterlet west of the centre of an otherwise flat and featureless floor and a small craterlet perched on the south western wall.
The plateau around Herodotus contains other remarkable features namely the partly ruined walled crater joining Herodotus to the south.  Three crater diameters south of Herodotus is an isolated dome with a central pit some times seen as elongated in small telescopes.  The plateau is fairly rich in craterlets and many rilles that seem to begin at small craters so there is plenty for me to return to and examine in greater detail this region of the Moon.
For members who are interested in Schroter's Valley I suggest you refer to the society library book Atlas of the Solar System page 204, as this shows in very good detail a composite photo of the valley taken by Apollo 15.







Jupiter


Observer Rev. Tim Gouldstone

Date           January 26th 1988
Time           17h 30m to 17h 42m UT
Seeing        Good some high cloud
Instrument  216mm Reflector Mag x216


NPR Uniform, no features seen.
NTB Broad with a suggestion of twinning p meridian and darker developments p/f meridian.
NTZ Featureless.
NEB Narrower than SEB but very disturbed on S margin.  At point indicated (1) very light across whole width.  Some features extend from S margin along EZ as shown.
S margin very disturbed and ill defined.
SEB Darker N and S margins with N margin straighter than S.  S margin has broad dark margin as shown.
Dark area p the GRS hollow on f limb.
STB Indistinct, only glimpsed on p side.
SSTB (?)  This area 'hazy' almost merges with SPR
GRS Hollow has dark N margin.

System 1 = 233° System 2 = 339°



February 4th 1988
Time not stated
Seeing Mod/Good, some high cloud
Instrument 216mm Reflector Mag x216


NPR Uniform, no detail seen.
NTB Broad and ill-defined with lighter central portion.
NTZ Featureless.
NtrZ Featureless.
NEB Dark N component S comp. very disturbed with lighter areas across whole NEB and arcuate features into EZn.  EZs no features.
SEB More uniform appearance than NEB with SEBn clearly differentiated near p limb.
Some darker areas extend across both N and S comps.
STrZ Some glimpes of darker area towards p limb, otherwise featureless.
STB Thin and barely perceived.
STZ Featureless SSTB more consp. than STB, merge with SPR.

System 1 = 273° System 2 = 310°

The SEB becomes very dark p the RSH as shown—dark on SEBs component (20h. 20m. U.T.)