Venus And Jupiter, 23 February 1999
Tuesday 23 February 1999 saw the closest apparent approach of Venus and Jupiter for many years. The weather was reasonably favourable around this date, offering naked eye observers the opportunity to view the spectacle evolve over successive evenings in the western sky shortly after sunset.
Monday 22 February. The weather on the evening before apparent closest approach was cold and clear. I observed Venus and Jupiter between 18:30 and 19:00 UT. At this time, the Sun had set and the planets shone brightly against a darkening western sky, approximately 1° apart, at an altitude of about 10°. Venus was at a slightly lower altitude and noticeably brighter than Jupiter (the planets shone respectively at magnitude -4.0 and magnitude -2.1). The planets also exhibited a marked colour contrast: Venus appeared pure white, whereas Jupiter appeared yellow-white. My 10x50 binoculars showed the two planets in the same field, and also revealed Jupiter's Galilean satellites. In the binoculars, Io and Callisto appeared as a single point of light to the east of Jupiter (the binoculars could not separate them) and Ganymede appeared to the west while the planetary disc occulted Europa.
Tuesday 23 February. The evening of apparent closest approach suffered from very hazy conditions affecting the whole sky. Only the Moon, planets and the brighter stars were visible. The haze created a very prominent halo surrounding the Moon at a distance of some 10 lunar diameters. Figure 1 shows the general orientation of the sky at 18:30 UT on 23 February. Despite the poor observing conditions, Jupiter and Venus were visibly very close together, presenting an unusual spectacle as they sank towards the western horizon. At 18:30 UT, the planets were at a separation of 514 arc-seconds (approximately one quarter of a lunar diameter) decreasing to only 481 arc-seconds as they set on the western horizon.
Figure 1. Sky vista on 23 February 1999.
Martin Cook, Garry Coleman and Mike Harlow observed the apparent close approach from Orwell Park Observatory using the 26 cm refractor with a wide-field eyepiece giving a magnification of approximately 50x. Both planets were visible in the field of view. Venus exhibited a slight phase, while the belts of Jupiter were very prominent. Figure 2 is an image taken with an SLR camera body at the prime focus of the refractor, showing Jupiter's flattened, brownish globe contrasting strongly with the brilliant white, gibbous Venus.
Figure 2. Venus and Jupiter through the Orwell Park refractor, 18.20 UT on 23 February 1999, ½ s exposure on 400 ASA slide film. (North up.)
Wednesday 24 February. The evening after closest apparent approach presented the best viewing conditions. In the early evening, circa 18:30 UT, the sky was very transparent and presented a marvellous view along the ecliptic. As on the previous day, Jupiter and Venus shone against a dark blue sky, this time with Venus at a higher altitude than Jupiter. Mercury was visible, just above the rooftops, and, further east along the ecliptic, Saturn and the Moon were too. The first magnitude star Aldebaran appeared close to the Moon (in fact, parts of China had witnessed a lunar occultation of Aldebaran in the preceding hours).
Although an apparent close approach of bright planets has little scientific value, it presents a beautiful spectacle. The next close approaches of Venus and Jupiter are in August 2014 and August 2016.