Planetary & Lunar Groupings
01 June 1980 - 24 May 2020
Although an apparent close grouping of planets, with or without the Moon, has no scientific value, it can provide an interesting spectacle for the observer, with multiple bodies appearing in the field of view of binoculars or a low power telescope.
- Alignment: a grouping of celestial bodies in apparent proximity.
- Appulse: apparent closest approach of two celestial bodies.
- Conjunction: two celestial bodies have the same right ascension.
Observations of planetary and lunar alignments by members of OASI are presented below.
24 May 2020, Grouping of Mercury, Venus & Moon, Nigel Evans
I missed out on the recent Mercury-Venus conjunction due to the weather, but on 24 May 2020 the sky cleared and another photo opportunity beckoned: Venus, Mercury and a young crescent Moon. The bodies were too low to see from the garden or the street, so I had to take to an upstairs window. Mercury was some 20° from the Sun and Venus only 15°. It is on occasions like this, where there is another bright "marker" object nearby, that it is possible to find and Mercury easily with the naked eye. I have only seen the planet with the naked eye on a handful of occasions previously.
07 April 2020, Appulse of Mars, Jupiter & Saturn, Nigel Evans
It's not often that three planets are visible close together in the sky, but on the morning of 07 April 2020, Mars, Jupiter and Saturn came within a 10° field of view. They were poorly placed for observers in northern latitudes, all at low altitude close to the SE horizon which meant that, unfortunately, due to various obstructions, they were not visible from my house or garden. The ban due to COVID-19 on non-essential travel meant that I could not drive to find a clear horizon, so I crept under cover of darkness into the middle of the cul-de-sac where I live to find a suitable vantage point from which to observe.
Mars, Jupiter and Saturn were at altitudes respectively 7°, 10° and 9°, with the Sun at -10°. My photograph of the planets is below. To my amazement, the photograph also shows two Galilean satellites of Jupiter and Saturn's largest satellite, Titan, at the limit of detection. Fainter objects could be found in the darker sky at higher altitude. Dwarf planet Pluto was also in the frame, some 46 arc-minutes south of Jupiter but, at magnitude 14, was well out of range!
29 October 2015, Appulse of Venus, Mars & Jupiter, David Murton & Neil Short
During October 2015, the planets Venus, Mars and Jupiter performed a merry dance in the morning skies! Mars and Jupiter made their closest approach on Saturday 17 October, coming within 0.22° of one another. Just over a week, later, on Sunday 25 October, Venus and Jupiter came within just over 1° of one another. On 26 October, Venus attained Greatest Elongation West (GEW), shining at a spectacular magnitude -5.1. On 28 October, the three planets lay within 1° of one another.
David Murton captured images 1-3 below from his home observatory at Bucklesham, south-east of Ipswich, in the early morning of 29 October 2015, shortly after the planets were at their closest. All photos were taken with a Canon 60da camera body and Canon lenses as follows:
- Figure 1. 18-55mm lens at 18 mm focal length. 1.5 seconds exposure, f8, ISO 800.
- Figure 2. 90-300mm lens at 200 mm focal length. 1.5 seconds exposure, f5.6, ISO 3200.
- Figure 3. 90-300mm lens (again) at 220 mm focal length. 3.0 seconds exposure, f5.6, ISO 2000.
Neil Short captured figure 4 from his home in Chelmsford. His report of the observation is as follows:
At 04:15 on the morning of 29 October, looking due east out of the window I made out two bright "stars" shining through the trees and bushes in our garden in central Chelmsford. I was instantly reminded of the coverage on the BBC that a three-planet alignment was due so went into the garden to determine if the two bright objects were indeed Venus and Jupiter, and whether Mars was also visible. Fortunately a gap in the trees allowed a clear view of the three planets. Back inside for my camera and the results are below, taken with a Canon 50HS (hand-held) set on auto. The inset was taken at higher zoom to confirm the unmistakable red colour of Mars.
30 June 2015, Appulse of Venus & Jupiter, James Appleton & David Murton
On 30 June 2015, an appulse 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 a balcony 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 Castor and Pollux, which provided convenient reference points 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.
27 June 2005, Appulse Of Mercury And Venus, Bill Barton, FRAS
Mercury is a relatively small planet, only about the size of Earth's Moon and, because it orbits close to the Sun, is always difficult to observe. However, in summer 2005, the planet Venus, much easier to find because it is physically larger, can be nearer to Earth and is intrinsically brighter, came within 0.07° of Mercury. To put this figure in perspective, consider that the Moon has an apparent diameter of approximately 0.5°; so, Mercury and Venus were apart in the sky approximately 14% of the diameter of the Moon. Of course, this was just an effect of perspective: although the planets appeared close together, it was a line-of-sight-alignment and they in fact were situated at vastly different distances from Earth.
The epoch of appulse was 19:00 UT on 27 June 2005. Mercury was emerging from superior conjunction on 03 June and approaching greatest elongation east (26°) on 09 July; Venus had emerged from superior conjunction on 31 March and also was heading towards greatest elongation east. Within a few days of closest approach, the planets did not appear to move so very far, so I hatched a plan to attempt to observe them each evening from 22 June to 29 June inclusive, in the hope of seeing them at least once.
An effective method for finding an object in the sky that is invisible to the naked eye is to point the telescope first at something that is visible and then move it by the appropriate offsets in right ascension (RA) and declination (dec) to find the object of interest. In the case of Mercury, I was able to download from the Internet a table published by Jonathan Shanklin (Director of the BAA Comet Section), listing offsets in RA and dec between the Sun, Mercury and Venus. My plan therefore was to open the Observatory at 18:00 UT each evening, point the Tomline Refractor at the Sun, then swing it round by the tabulated offset in RA, search in dec for Venus and, once located, search for Mercury in close proximity.
Below is a summary of each evening's observations:
|Wed 22 June
||Offset the Tomline Refractor from the Sun, but unable to find Venus. Must be doing something wrong! However, we still have a few evenings to practice. Hoping for better luck in future...
|Thu 23 June
||Cloudy. Called off observations before leaving home.
|Fri 24 June
||Observations impossible due to lack of qualified personnel to open the dome at the Observatory.
|Sat 25 June
||No qualified assistant was available to help open the dome at Orwell Park so I abandoned thoughts of observing and instead travelled to the BAA Exhibition Meeting in Cambridge with OASI's Chairman and Treasurer, where we manned the stand of the Society for the History of Astronomy.
|Sun 26 June
||It being a Sunday, I didn't expect much support; however, two members of OASI expressed an interest. We duly opened the Observatory at 18:00 UT on an excellent evening with clear blue skies. By 18:20 UT we had found Venus, small and round, but where was Mercury? Four magnitudes fainter, it was never going to be easy to find. After 20 minutes of searching I found it, slightly to the east of Venus. Success! My two fellow observers also saw both planets. We used an eyepiece of 32 mm focal length, giving a magnification of approximately 120x. All set now for tomorrow evening's attempt at closest approach.
|Mon 27 June
||We opened the Observatory to plan at 18:00 UT and, using the previous day's experience, were able to locate both planets by 18:15 UT. Tonight, Mercury appeared north of Venus and the two planets were noticeably closer than on the previous evening. Five observers watched the planets until 20:10 UT when we shut the Observatory. Mike Harlow attached a camera to the Tomline Refractor and photographed the event.
|Tue 28 June
||Observations were prevented by poor weather: nothing but haze was visible through the eyepiece in the direction of Mercury and Venus.
|Wed 29 June
||This was the last night of observations and, by now, the two planets were visibly further apart and would no longer be visible together in the field of view of the Tomline Refractor. The sky was less hazy than on the previous evening and, although Venus was clearly visible in the eyepiece, the sky was just too bright to discern Mercury.
So, in summary: I planned eight nights of observing, made five trips to Orwell Park, and recorded two successful observations. Not a bad score! I would like to thank Jonathan Shanklin for making his positional figures available. The observers were (in alphabetic order): James Appleton, Garry Coleman, Nicky Gillard, Ken Goward, Mike Harlow, Gerry Pilling, Pete Richards, Ted Sampson, Mike Whybray.
26 April - 14 May 2002, Planetary Alignment, Nigel Evans & Roy Gooding
From late April until mid-May 2002, all five of the classical planets (Mercury, Venus, Mars, Jupiter and Saturn) appeared together in the western sky after sunset. The minimum separation was 33° on 13 May. Several members of OASI photographed the spectacle, among them Nigel Evans and Roy Gooding. On every clear evening in late April and early May, Nigel attempted to photograph the five planets together. Generally, he limited the exposure to that given by the 500 / focal length (mm) rule. Only when the Moon was present did he use a driven mount. Roy captured three of the planets in a photograph taken at Orwell Park Observatory on 01 May. A selection of the images is below.
26 Apr 2002. (Nigel Evans.)
01 May 2002. (Nigel Evans.)
01 May 2002. (Roy Gooding.)
04 May 2002. (Nigel Evans.)
07 May 2002. (Nigel Evans.)
14 May 2002. (Nigel Evans.)
06 April 2000, Planetary and Lunar Conjunction, James Appleton
A close conjunction of the two day old crescent Moon, Saturn, Mars and Jupiter occurred on 06 April 2000, low in the western horizon, shortly after sunset. I took the following photograph from East Ipswich at 20:00 UT on 06 April 2000 using a 80 mm zoom lens with 1000 ASA print film. The conjunction preceded a spectacular auroral display later in the evening.
23 February 1999, Venus And Jupiter, James Appleton
Tuesday 23 February 1999 saw the closest apparent approach of Venus and Jupiter for many years. The weather was reasonably favourable in the few days beforehand, 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 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 (magnitudes were respectively -4.0 and -2.1). The planets also exhibited a marked colour contrast: Venus appeared pure white, whereas Jupiter appeared yellow-white. 10x50 binoculars showed the two planets in the same field of view, and also revealed Jupiter's Galilean satellites. 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. The following diagram shows the general orientation of the sky at 18:30 UT. 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.
Sky 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. An image taken with an SLR camera body at the prime focus of the refractor is below. It shows Jupiter's flattened, brownish globe contrasting strongly with the brilliant white, gibbous Venus.
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 offered the best viewing conditions, with a very transparent sky. Around 18:30 UT, Jupiter and Venus shone against a dark blue background, this time with Venus at the higher altitude. Mercury was visible, just above the rooftops, and, further east along the ecliptic were Saturn and the Moon. The first magnitude star Aldebaran was close to the Moon (in fact, parts of China had witnessed a lunar occultation of Aldebaran a few hours earlier).
01 June 1980, Mercury & Venus, Roy & Catherine Adams
An appulse of Mercury and Venus was predicted to occur at 18:88 UT on 01 June 1980, the two planets coming within ⅓° of one another, Mercury at magnitude -0.5 and Venus at magnitude -4.4.
Alerted to the appulse by the OASI Newsletter, we aimed to observe the event. Cloud persisted early in the evening and it did not, initially, look as if we had much chance. Then, just before 21:00 UT, while watering the garden, we suddenly realised that the sky was clear and rushed to the front of the house to see if the area of the sky around the setting Sun was clear.
It did not take us long to find Venus and then, after a little while, Catherine thought that she spotted Mercury with the naked eye. Quite a feat to be sure, but yes, on looking through a 5.6 cm handheld refractor at 40x magnification, there it was. We took it in turns to watch for over a quarter of an hour and made the following drawing of the position of the planets.
Venus was at low altitude and its disk therefore appeared distinctly reddish and devoid of its excessive glare! Indeed, at the end of our observation, the planet was only a couple of degrees above the horizon.