Planet Update

Saturn will be at opposition on December 31. (Please see recent features on Saturn in the archives.)

Mars is in rapid forward motion against the star background (W to E), while Saturn is retrograding slowly (E to W). Dia. 1 shows the position of the two planets on December 15 at 21h 00m, together with a trace of their movements for the succeeding 60 days.

On the 15 December the two planets will appear about the same brightness. Mars is often referred to as the red planet but some observers may be surprised to find Saturn looking much the same colour.

Dia. 1 Sky looking SSE at 21h 00m on December 15. Click the image for an enlargment

(The colour of both planets varies. In the case of Mars this is due to atmospheric effects whereas with Saturn the change is less noticeable and is related to the orientation of the ring system as seen from Earth.)

Mars continues to fade so that by mid-February it will be about the same magnitude as Aldebaran, which it will also resemble in colour. (Aldebraran is a red giant star.)

Mercury and Venus are both to the east of the Sun during the first part of December. Dia. 2 shows the sky looking south at 16h 00m on December 15. It

Dia. 2 Sky looking S at 16h 00m on December 15. Click the image for an enlargement

should be possible to see Venus and, if the sky is free from haze and cloud, it may also be possible to get a glimpse of Mercury with binoculars or even with the naked eye.

The window of opportunity for Mercury will be brief (12th to 17th) since it rapidly draws towards the Sun, to be at Inferior Conjunction of the 27th. Venus, on the other hand, will draw away from the Sun and will be a brilliant object low down in the evening sky by the end of the year. On Christmas evening the young Moon will appear below the planet.

Jupiter, rising at a little after 23h on the 15th, will have the Moon for company this night.

Winter Solstice

Winter Solstice occurs this year on December 22nd. This day the Sun has its maximum southerly declination with an altitude, here in Orkney at transit (true or apparent noon - 12h 11m), of a little over 7.5 degrees.

Frequently referred to as the shortest day, this is another of those misnomers that has become acceptable through usage. (The Earth does not obligingly rotate faster on its axis for the day!)

Again from Orkney, the Sun is above the horizon for a little over six hours around the time of the winter solstice. On the other hand, the Sun begins to rise earlier as from the 29th even though it sets later after December 17th. From this date the evenings may be said to "draw out", though this is hardly perceptible to the casual observer until well into January.

Interestingly new moon occurs on December 23rd at 09h 42m, within a day of the solstice.

JV 07/12/03