Venus & Jupiter

Venus crosses the celestial equator between 14h and 15h on Monday, February 9th. That evening it will set almost due west at 21h 06.

From the Rousay School looking up the Sourin Valley of an evening, Venus has already become a splendid naked eye object. At magnitude -4.1 it outshines the brilliant Jupiter (rising a little north of east at 19h 20m on the 9th) five fold. Those with a clear horizon east and west will have the opportunity at 20h 15m on the 9th February of seeing Venus and Jupiter almost diametrically opposite one another in the sky and at the same altitude - approximately 6 degrees.

Observing Venus

For all its naked eye brilliance, Venus is a disappointing telescopic object. It is in fact its very brilliance that is responsible for the disappointment. The exceptionally high albedo of Venus (the greatest of any solar system planet) is due to a permanent cloud cover over the entire planet. Seen in a powerful telescope Venus is a dazzling, almost featureless object. It is therefore necessary to view Venus optically during daylight or very strong twilight. The serious observer will use a range of filters in order to detect the illusive markings which are visible from time to time.

But for the casual telescopic observer the most noticeable feature is Venus's phase. At present the planet is a little under 75%. Towards the second half of March Venus will be approaching 50%. By then it will have increased in diameter to around 23 arc seconds (compared to Jupiter's equatorial diameter of 44 arc seconds) and will be an easy object in a good spotter telescope working with a power of x30 or more.

I have deliberately withheld the date of dichotomy (when the geometrical or theoretical phase is exactly 50%) since there is still considerable debate over the time of apparent or observed dichotomy and observers may like to make their own assessment. This so-called phase anomaly of Venus - often referred to as the Schröter effect - may be verified by observing Venus around the time of dichotomy. A telescope able to take a power of at least x100 should be used since the anomaly is almost certainly due in part to the relatively small angular diameter of the planet.

Further detail on the Schröter effect will appear in the article on the Transit of Venus to appear later in these notes.

JV
8/02/04

Venus in 2004

The planet Venus in 2004 will dominate our evening and, from July, our morning skies. Not only this, but on June 8 the planet passes in front of the Sun to give the first Transit of Venus since 1882. (Readers should recall there was a Transit of Mercury last year in May)

This event will be treated in greater detail nearer the time.

Already by the last week of 2003, Venus had become a conspicuous evening object low down in the SSW. The crescent Moon will be some 2º below Venus on the evening of Jan 24.

As a result of its forward motion in Right Ascension and rapid increase in declination the planet will set about 4 minutes later every night until by March 27 it sets in the NW after midnight. Greatest elongation East (46º) occurs just two days later on the 29th. (Coincidentally, Mercury also reaches its maximum eastern elongation on the same day a mere 5 hours earlier - a rare phenomenon.)

Throughout April Venus closes on Mars. It passes very close to the Pleiades cluster on April 2-3, by which time it will appear to approach the bright star El Nath (ß Tauri). The two planets are not destined to come together however. At their closest (around April 27) they will be a little under 6º apart; after this Venus moves inexorably from east to west towards the Sun.

Readers will also recall from April/May 2002 the array of all the naked eye planets in the evening sky. This year in March/April there will be a similar but less spectacular alignment (Jupiter being situated well away from the main grouping).

The brilliance of Venus

Greatest brilliancy occurs this year between April 16 and May 15, and between July 5 and July 24.

I recall as a teenage schoolboy reading that Venus at its brightest could cast a shadow when viewed in a dark sky. With anticipation I waited months until from my bedroom, which faced east, I was able to confirm this fact for myself. That was in October 1951 when Venus was at maximum brilliance (mag. -4.6).

I still have my notes from that time, quote: "The planet was so bright the window slats were shown as shadows on the cream wall of the room". I would not have had the same opportunity today from that site (Brentwood, Essex), nor indeed from my present location on Rousay. The all pervading, all night artificial light culture has seen to that.

JV 6/01/04