Mercury is the nearest planet to the Sun. It is a small terrestrial-type world that is roughly halfway in size between the Moon and Mars. Its distance from the Earth means that we see its surface at a low order of resolution; and the craters and escarpments revealed on its surface by Mariner 10 are not recognisable in the telescope. Note. In the following descriptions the abbreviation "CM long." means the longitude of Mercury's Central Meridian (the north-south centreline of the planet's whole disc) on the day of the observation. These CM long. values relate to the longitude system shown on the chart below.

Frank Melillo (NY, USA) captured Mercury on CCD. Just visible near the terminator is the curved dark shading known as the Solitudo Phoenicis, merging towards the south with the Solitudo Criophori.

Mercury is always close to the Sun in the sky and a very few weeks after it becomes visible, low down in the dusk or dawn, its rapid orbital motion carries it out of view again. These brief appearances in the twilight make it possible to compare Mercury with some of the brighter stars and planets. Frederick Butler (London, UK) did so in December 1999 when Mercury rose in the morning sky, just as Sirius was setting in the west. Using 10x50 binoculars he noted that both objects looked about equal in brightness, suggesting that Mercury was one stellar magnitude brighter than the value given in the BAA Handbook. This is not the first time that Mercury has been estimated to be brighter than predicted. Such comparisons are not part of our formal programme, but we are interested to receive them.

Mercury generally displays a duller tone than its brilliant planetary neighbour, Venus, yet it may look tinged with colour. On 2000 August 6 at 11.20 UT, using an 8cm Refractor (x225) in broad daylight at Coneysthorpe (UK), Robert Steele had no difficulty picking up Mercury when its tiny gibbous disc looked distinctly yellow. Yellow-orange colours and pink or red tinges are often mentioned by observers; and the warm colours of a twilight sky may impart themselves to Mercury's image in the telescope. These colour sketches were made by the late Paul Doherty (Stoke on Trent, UK). From top to bottom in each sketch the darker shadings are: Solitudo Persephones, Solitudo Criophori, Solitudo Phoenicis. The small patch at "10 o'clock" near the limb is the Solitudo Atlantis.

For long, observers have made out dusky patches on Mercury's tiny disc, but there are intriguing bright spots also. William Frederick Denning, a distinguished amateur observer of meteors as well as of the planets, made out both types of markings in a classic series of dawn observations with his 25cm altazimuth reflector in November 1889.

 A hundred years later David Graham (Brompton on Swale, UK) had a "Denning view" of the same regions on 1986 December 06. This is one of the most significant amateur observations of Mercury, for later Graham wrote "On the afternoon of Thursday, December 11 (1986), I was observing the gibbous Moon with the naked eye when I noticed a very bright spot near the limb close to the M. Nectaris and Foecunditatis… Well bearing this in mind I was thinking of the bright area I noticed near the limb of Mercury… I cannot but help noting the rough similarity between the naked-eye Moon and the telescopic view of Mercury." Thus a possible connection may exist between the bright spots seen on Mercury from Earth and areas of bright or rayed craters imaged by the Mariner 10 spacecraft.

Taking advantage of excellent seeing conditions on 2000 June 07, Mario Frassati (Crescentino, Italy) queried a "very clear area: ray system?" in the region of longitude 285º, latitude -30º (corresponding approximately to the area just south of the Solitudo Alarum) that was not covered by Mariner. This intriguing observation by one of Italy's finest planetary observers shows a light circular area in Mercury's southern hemisphere near the terminator. An extension of the bright patch is shown bisecting the darker Solitudo Alarum to the north. Note also the very dark south cusp, making it look blunted or truncated. The large dark feature shown near the bottom (north) is the Solitudo Aphrodites. The next reasonable opportunity to observe this region will occur at the planet's morning elongation between 2001 July 10 to 20. Will further observations confirm the bright patch or Frassati's division (of the S. Alarum)? Excellent seeing will be necessary, but the challenge is there.

Visual colour filters are suitable for enhancing Mercurian disc features: light blue or green for darker markings, while orange, or light yellow and light green stacked together, may give more distinct views and stronger contrasts with bright areas on the disc. During 1995 and 1996 David Gray (Spennymore, Co Durham, UK) made these detailed disc drawings with filters.

The terminator of Mercury shows fairly frequent irregularities. Such appearances are undoubtedly caused by the presence of contrasting regions on the disc. On 1995 May 13 Ian Phelps drew one such instance. The dark features near the terminator are tentatively identified (top to bottom) as Solitudo Martis and Solitudo Admetei.

The cusps also display interesting appearances. Observers remark upon a fade off in illumination at the cusps, making them appear quite dim (as shown in the drawing by JB Murray), or even giving them a blunted appearance. Murray used the 46cm Refractor at the University of London Observatory; and in the early seventies he worked with the renowned French planetary scientist, Dr Audouin Dollfus to produce the best pre-Mariner albedo chart of Mercury.

Mercury looms out of the evening sky. John B Murray, 1968 February 2, 17.26 UT, 46cm Refractor x350, seeing fair.

Mario Frassati recently recorded a dark aspect to the south cusp of Mercury .

Mercury 2001 January 30, 16.30 UT, by Mario Frassati (Crescentino, Italy), 20cm SCT x250-400, W8 light yellow filter, seeing Antoniadi III. CM long. 98 degrees. The dark features near the terminator are (from top to bottom) Solitudo Martis, Solitudo Lycaonis, and Solitudo Admetei. Not also the bright spots on the disc at "7 o'clock" and "10 o'clock".

And by contrast, Richard Baum rendered these views of an unusually bright aspect to Mercury's cusp regions.