Russell Eberst's Sky View

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March 2018

The Spring equinox (for the northern hemisphere) arrives on March 20. The Sun crosses the celestial equator on March 20 at 16.15 U.T. going northwards, marking the exact equinox. "Equinox" indicates that the length of the day and night are expected to be equal on that date. If the tables of sunrise and sunset are inspected, it will be found that at the equinox, the length of daytime exceeds that of nighttime by a few minutes. This is due to the refractive effect of the Earth's atmosphere which raises the apparent position of the Sun at sunrise and sunset by almost a degree, advancing the time of sunrise and delaying the time of sunset. There is also the effect caused by the times of sunrise and sunset being measured when the upper limb (or edge) of the Sun is on the horizon, and not the centre of the Sun. The actual date on which there are twelve hours of daylight and twelve of night is nearer March 18. The rapid change in the time of onset of the evening dusk means that the familiar stars of winter move quickly towards twilight and to being lost in the Sun's glare. Nevertheless, the prominent winter stars such as Orion and its surrounding assemblage will remain visible throughout March. The ecliptic which marks the paths of Sun, Moon and planets among the stars, reaches its highest angle relative to the western horizon, in the evenings during March. This means that planets such as Mercury and Venus are positioned more favourably than at any other time of the year. Venus is slowly emerging from behind the Sun, having reached "superior conjunction" on January 9. It has already been spotted by amateurs as it extends its separation from the Sun, to be 19° by the end of the month. This should make it reasonably easy to spot in the western sky, low down as the sky darkens. It sets an hour after the Sun at the beginning of March, and almost two hours after the Sun at the end. It will be accompanied by the other inner planet, Mercury, during the first three weeks of March. This period will be the best opportunity to spot the ever elusive Mercury during any evening in 2018.

To do this, first scan the bright twilight western sky using binoculars. Please wait until after you are sure that the Sun has completely set. Within half-an-hour it should be able to spot Venus as a prominent speck. Around March 18, Venus will appear 3°.8 to the south of Mercury, with both these 'inferior' planets in the field of view of most binoculars. On the same evening, the very thin crescent Moon will pass about 5° to the south of Venus, giving a delightful sight for observers of solar system objects. Mercury dives in towards the Sun during the rest of March, leaving Venus to command the western sky after dark with a very close pass on March 29 to the planet Uranus, which will hardly be detectable. The Moon moves on and Earthshine (also known as 'the old Moon in the young Moon's arms) should be visible on March 18 and a few following evenings. A dim full-disc Moon cradled in the bright crescent will be visible, the faint illumination resulting from the intense light of the Full-Earth lighting up the lunar landscape. The planet Jupiter also joins in the list of planets becoming visible in the evenings. It rises before midnight although it is still technically a 'morning' object. It is in Libra, well south of the equator, so that it fails to reach 20° elevation from Central and northern Scotland, even around 04.30 a.m. when it is due south. The waning Moon passes Jupiter on March 7, and on March 10 is near Mars. The next morning it is close to Saturn. Jupiter's four large 'Galilean' moons pursue their never ending orbits, and on March 11 can all be found on the western (preceding) side of the planet. Our Moon once again reaches Full phase twice this month. In January it was full on the 2nd and 31st, and exactly the same dates are true for March. The March 31 event constitutes a 'blue' moon, using one definition of that title. A repeat performance occurs in the year 2037.

In space exploration, mankind's intervention has intensified. A space launch from New Zealand on January 21 saw a number of small satellites put into polar orbit. One of these is a 1-metre polyhedral object that has little if any scientific purpose. It goes by the name 'Humanity Star'. Its owners indicated that it would remain in orbit for 9 months but my estimate is that it will be lucky to last half of that. The orbit was initially largely in shadow, but from March 9 it should begin a short visibility for all latitudes. Another satellite that is nearing the end of its life is the Chinese space station, Tiangong 1. Now abandoned, it was designed as a manned laboratory and as an experimental docking module, firstly between Tiangong-1 and an unmanned Shenzhou spacecraft in November 2011. Thereafter came 2 manned missions, Shenzhou 9 and Shenzhou 10. That mission included the first female Chinese astronaut (Liu Yang). By the end of 2015, the last orbit boost was achieved and in March 2016 it was announced that control had been lost, and that the Tiangong 1 station would lose altitude to eventually burn up in the atmosphere. Satellite trackers followed its steady decline, and it is now expected to reach its fiery decay at the very end of March. Some of its structure may survive the rapid passage and reach the ground (or more probably the sea). Since it orbits between latitudes 43°N and 43°S, it is only in that region that there is any possibility of debris hitting the Earth. So London is under a tiny threat. Oh, that's London, Ontario not London, England. With a lot of media attention, a lot of skywatching is to be expected. Meanwhile, in the U.K. we put our clocks forward on Sunday, March 25.

Moon phases:

  • Full Moon: March 2 and 31
  • Last Quarter: March 9
  • New Moon: March 17
  • First Quarter: March 24

Sky View Image

The maps show the sky at 23.00 GMT on the 1st, 22.00 GMT on the 16th and 21.00 GMT (22.00 BST) on the 31st. Summer time begins at 01.00 GMT on the 25th when clocks go forward one hour to 02.00 BST.