Mercury
Mercury, the innermost planet, is now heading towards greatest eastern elongation (GEE), which it reaches on March 15th. Observers at northern-based locations should be able to spot the elusive planet just after sunset during the first 3 weeks of the month, when it appears low down above the western horizon. Each subsequent evening, from March 1st, it gradually improves in altitude with a longer visibility until GEE is reached. The planet will then be positioned 18 degrees from the Sun and shine at magnitude -0.4. After that, Mercury gradually sinks back towards the horizon until about 10 days later when it's finally lost to the bright twilight sky. From northern locations this also happens to be the best evening apparition of the year.
During the first few days of the month, Venus and Mercury appear close together. Venus is 12x brighter than its inner neighbour and on March 5th the two planets are separated by 1.4 degrees. Binoculars will assist locating Mercury, especially in the bright twilight, but don't use them until after the Sun has set. From southern latitudes, Mercury is not so well placed at this time. At GEE it sets only forty minutes after the Sun and will be difficult to spot in twilight. However, much brighter Venus is situated four degrees to the south and acts as a good marker.
Venus
Venus, mag. -3.9, can be seen low towards the west after sunset. As the month progresses the brilliant planet rises a little higher in the sky each subsequent evening and by months end, from northern temperature latitudes, sets about 90 minutes after the Sun. For those further south, the planet sets an hour after the Sun on the last day of the month.
As mentioned above, Mercury and Venus are positioned close together during the start of the month. On March 19th, the thin waxing crescent Moon passes 4 degrees south of Venus and on March 29th, Venus passes only 0.1 degrees south of Uranus. At mag. +5.9, Uranus is almost 10,000x fainter than Venus. Binoculars or a small telescope will be required to spot distant Uranus, although both planets will easily fit in the same field of view.
Mars
Mars begins the month moving direct in Ophiuchus. However, the planet moves fast and it's not long before it crosses into Sagittarius (March 12th) and by months end lies only a couple of degrees southwest of Saturn (mag. +0.5). The planet continues to brighten, starting the month at magnitude +0.8 and increasing by half a magnitude to +0.3 by month's end. During the same period, its apparent size increases from 6.7 to 8.4 arc seconds. At medium to high magnifications, it's now possible to make out some of the main surface details with a telescope, such as the Syrtis Major.
Mars, like Jupiter and Saturn, is current better placed for observation from southern and tropical locations. From such locations, the planet rises just after midnight by months end and appears high in the sky. From mid-latitude northern latitudes the 'Red planet' appears much lower down and has a shorter visibility period. At months end it rises early morning, around 4 hours before the Sun.
On March 10th, the waning crescent Moon passes 4 degrees north of Mars. On the last day of the month, Mars passes just a degree north of magnificent globular cluster, M22.
Mars and Saturn during March 2018 (credit:- freestarcharts) - pdf format (credit:- freestarcharts)
Jupiter
Jupiter now rises just after midnight at the beginning of the month from northern temperate latitudes and even earlier for those located further south. The gas giant is located in Libra and brightens from magnitude -2.2 to -2.4, with its apparent size increasing from 39.1 to 42.5 arc seconds as the month progresses. With binoculars or small telescopes up to 4 Galilean moons are visible. A small scope will also reveal features such as the northern and southern equatorial bands and the Great Red Spot, although it has been diminishing in size for some time now.
On March 7th, the waning gibbous Moon passes 4 degrees north of Jupiter. Two days later Jupiter begins retrograde motion, which signals the start of this year's opposition period.
Jupiter during March 2018 - pdf format (credit:- freestarcharts)
Saturn
Saturn, mag. +0.6, continues to move direct in Sagittarius, north of the "teapot" asterism. The beautiful "Ringed planet" remains a morning object, although by month's end it's visible from just after midnight from southern temperate locations. However, those located further north will have to wait up to 4 hours longer to spot the planet. As previously mentioned, at months end, Mars appears a couple of degrees southwest of Saturn. This offers a good opportunity to compare and contrast the apparent difference in colour between the two planets. Mars is distinctly orange, with Saturn creamy or off-white in colour.
When seen through a telescope, Saturn is a wonderful sight. A small 80mm (3.1-inch) scope easily reveals the ring system, which is currently wide open at a tilt of 26 degrees to the line of sight. A 150mm (6-inch) or 200mm (8-inch) instrument shows a wealth of details, such as planetary cloud formations, ring divisions and up to half a dozen satellites. During the month, the apparent diameter of Saturn's disk increases slightly from 16 to 17 arc seconds.
On March 11th, the waning crescent Moon passes 2 degrees north of Saturn.
Uranus
Uranus, mag. +5.9, remains an early evening binocular object during March. The seventh planet from the Sun, located in Pisces, is visible towards the west as soon as it's dark enough. For those located at temperate northern latitudes it can be seen for about 3 hours on March 1st. However, it's not long before the bright twilight closes in and by months end, Uranus will be difficult to spot. From southern locations, the visibility period of Uranus is shorter still. As previously mentioned on March 29th, much brighter Venus passes 0.1 degrees south of the planet and acts as a perfect marker.
On March 19th, the thin waxing crescent Moon passes 5 degrees south of Uranus.
Neptune
Neptune continues to move slowly direct in Aquarius as it heads towards solar conjunction on March 4th.
For observers at tropical and southern locations the distant planet reappears at month's end, low down above the eastern horizon just before sunrise. At mag. +8.0, it's beyond naked eye visibility but can be glimpsed with binoculars and small scopes.
From northern temperate latitudes, Neptune remains inconveniently placed throughout March and is not readily observable.
Solar System Data Table - March 2018
| Date | Right Ascension | Declination | Mag. | App. Size | Illum. (%) | Dist. (AU) | Constellation | |
|---|---|---|---|---|---|---|---|---|
| Sun | Mar 01 | 22h 46m 30.4s | -07d 46m 52.0s | -26.8 | 32.3' | 100 | 0.991 | Aquarius |
| Sun | Mar 15 | 23h 38m 20.8s | -02d 20m 31.7s | -26.8 | 32.2' | 100 | 0.994 | Pisces |
| Sun | Mar 31 | 00h 36m 41.1s | 03d 57m 08.6s | -26.7 | 32.0' | 100 | 0.999 | Pisces |
| Mercury | Mar 01 | 23h 24m 37.8s | -04d 44m 35.3s | -1.3 | 5.3" | 93 | 1.262 | Aquarius |
| Mercury | Mar 15 | 00h 42m 23.1s | 06d 43m 45.6s | -0.4 | 7.3" | 47 | 0.927 | Pisces |
| Mercury | Mar 31 | 00h 43m 19.2s | 08d 02m 35.2s | 5.3 | 11.1" | 1 | 0.608 | Pisces |
| Venus | Mar 01 | 23h 33m 51.6s | -04d 18m 54.8s | -3.9 | 10.0" | 98 | 1.663 | Aquarius |
| Venus | Mar 15 | 00h 37m 22.5s | 02d 51m 44.7s | -3.9 | 10.2" | 96 | 1.630 | Pisces |
| Venus | Mar 31 | 01h 50m 29.5s | 10d 48m 36.2s | -3.9 | 10.6" | 94 | 1.581 | Aries |
| Mars | Mar 01 | 17h 16m 35.4s | -22d 46m 41.1s | 0.8 | 6.7" | 89 | 1.402 | Ophiuchus |
| Mars | Mar 15 | 17h 52m 09.1s | -23d 23m 20.2s | 0.6 | 7.4" | 88 | 1.268 | Sagittarius |
| Mars | Mar 31 | 18h 31m 37.0s | -23d 33m 27.7s | 0.3 | 8.4" | 88 | 1.117 | Sagittarius |
| Jupiter | Mar 01 | 15h 23m 07.1s | -17d 20m 33.0s | -2.2 | 39.1" | 99 | 5.046 | Libra |
| Jupiter | Mar 15 | 15h 23m 21.6s | -17d 19m 15.2s | -2.3 | 40.7" | 99 | 4.838 | Libra |
| Jupiter | Mar 31 | 15h 20m 37.5s | -17d 06m 53.1s | -2.4 | 42.5" | 100 | 4.636 | Libra |
| Saturn | Mar 01 | 18h 30m 34.7s | -22d 22m 24.5s | 0.6 | 15.9" | 100 | 10.476 | Sagittarius |
| Saturn | Mar 15 | 18h 34m 25.8s | -22d 19m 16.8s | 0.5 | 16.2" | 100 | 10.257 | Sagittarius |
| Saturn | Mar 31 | 18h 37m 19.2s | -22d 16m 34.1s | 0.5 | 16.6" | 100 | 9.992 | Sagittarius |
| Uranus | Mar 01 | 01h 35m 59.3s | 09d 25m 14.6s | 5.9 | 3.4" | 100 | 20.577 | Pisces |
| Uranus | Mar 15 | 01h 38m 29.1s | 09d 39m 57.2s | 5.9 | 3.4" | 100 | 20.729 | Pisces |
| Uranus | Mar 31 | 01h 41m 42.0s | 09d 58m 36.3s | 5.9 | 3.4" | 100 | 20.845 | Pisces |
| Neptune | Mar 01 | 23h 00m 46.8s | -07d 18m 09.7s | 8.0 | 2.2" | 100 | 30.932 | Aquarius |
| Neptune | Mar 15 | 23h 02m 45.3s | -07d 06m 03.7s | 8.0 | 2.2" | 100 | 30.922 | Aquarius |
| Neptune | Mar 31 | 23h 04m 55.7s | -06d 52m 50.2s | 8.0 | 2.2" | 100 | 30.843 | Aquarius |