Appulse of Venus & Jupiter,
30 June 2015
On 30 June 2015, an appulse (apparent close approach) of Venus and Jupiter occurred in the evening twilight sky. At their closest, the planets came within 20 arc-minutes of one another. Images of the appulse, taken from one of the balconies at Orwell Park Observatory, are below as follows.
- David Murton. Figure 1. Wide-angle shot of Venus and Jupiter with one of the chimneys of Orwell Park School in silhouette against the sunset (bottom). Canon 1100D camera.
- James Appleton. Figure 2. Wide-angle shot of Venus and Jupiter about to disappear behind a chimneys of Orwell Park School. Canon Powershot SX220 camera.
- David Murton. Figure 3. Close-up of Venus and Jupiter. Note the Galilean moons of Jupiter strung out in-line in its equatorial plane and the slightly gibbous appearance of Venus (both visible in the full image, not the thumbnail). Unfortunately, as the planets were at low altitude, no other features are visible. Skywatcher 200PDS on HEQ5 mount, QHY5L II camera, 4x Powermate,
Prior to the appulse, in late May - early June, James had tracked the motion of the planets. Throughout the period, they were in the neighbourhood of α and β Geminorum, Castor and Pollux respectively, which provided a convenient reference point against which to judge motion. During the three days 21 – 24 May, the crescent Moon passed the pair, the conjunction forming a very photogenic grouping.
On each clear evening during 21 May – 10 June, James photographed the western sky after sunset. (The project was terminated when the planets disappeared in the evening twilight behind a neighbour's house.) He adjusted the images to a common scale and alignment (using the fixed stars Castor and Pollux as markers), highlighted Castor, Pollux, the Moon, Venus and Jupiter as foreground objects and set everything else as transparent background and overlaid the images. Adding as background the terrestrial landscape looking west produced the composite figure 4, below. In the figure, the numbers below the Moon and planets represent dates in May and June. The position of Jupiter is shown for the same dates as Venus, and in the same sequence (numbers are not given for Jupiter as they would be too squashed together). Castor and Pollux are marked. Note that the images of the stars and planets have been slightly retouched to enhance visibility: the image covers an area of approximately 600 square degrees and the objects un-retouched would appear as tiny dots.
The Moon clearly shows the largest apparent daily movement, followed by Venus, then Jupiter. The motion of Venus appears approximately linear and prograde over the period shown, with daily increments in RA slightly reducing over time; this is in line with theory. The path of Jupiter also appears prograde, but notably less regular; this is due to its increased apparent distance from Castor and Pollux, magnifying the effect of alignment errors in composing the image.
Table 1 lists the apparent daily motions of the planets over the period in question, calculated using the NASA ephemeris DE-430. As expected, the dominant motion of the bodies is in RA.
Table 1. Average daily planetary motions, 21 May - 10 June 2015.
To the naked eye, the motion of Venus was apparent each night as it sped towards and then away from Pollux. Greatest eastern elongation occurred on 06 June. The daily motion of Jupiter, however, was not obvious.
Fig. 4. Motion of the Moon, Venus and Jupiter.