Europe’s Philae probe to attempt first touchdown on comet
In an exciting month in astronomy and space exploration, November should bring the first soft landing on a comet when the European Space Agency’s Philae craft detaches from the Rosetta probe and drops gently onto the icy nucleus of Comet Churyumov-Gerasimenko.
Our sky at nightfall s similar to that of a month ago although, with our return to GMT, darkness arrives more than two hours earlier in the evening. Mars continues as the only bright planet at these times, visible low in Edinburgh’s south-south-western sky and fading only a little from magnitude 0.9 to 1.0 as it tracks eastwards above the Teapot of Sagittarius.
However, even though Mars is drawing closer to the Sun, its altitude at the end of nautical twilight improves from 5° to 9° during November as the Sun plunges more than 7° southwards in the sky and Mars edges almost 3° northwards. This also means that Mars-set in the south-west occurs at about 19:05 throughout the period. It stands below the young crescent Moon on the 26th.
Sunrise/sunset times for Edinburgh change from 07:19/16:33 GMT on the 1st to 08:17/15:45 on the 30th as the duration of nautical twilight at dawn and dusk extends from 83 to 93 minutes. The Moon is full on the 6th, at last quarter on the 14th, new on the 22nd and at first quarter on the 29th.
Comet Churyumov-Gerasimenko lies 6° south-east of Mars on the 12th but is a very dim telescopic object some 450 million km from the Sun. On that day Philae is due to unlatch from Rosetta and take about seven hours to fall 22.5km, coming to rest on tripod legs at about 16:00 GMT atop the head of the comet’s strange “rubber-duck” shape. To stop itself bouncing off into space in defiance of the comet’s feeble gravitational pull, it should then fire a tethered harpoon to anchor itself to the surface.
The comet’s 6-year orbit is carrying it closer to the Sun, eventually to reach perihelion at a distance of 186 million km next August. Meantime, its activity is picking up and Rosetta is imaging jets of dust and gas emerging, mainly from the duck’s neck region at present. With Philae in position to also monitor conditions at the surface, and even below the crust using sonar, seismographs and permittivity probes, our knowledge of what makes comets tick should soon be transformed.
The Summer Triangle of Vega, Deneb and Altair, lies in the west at our map times as Orion rises in the east below Taurus and the Pleiades. The Square of Pegasus stands high on the meridian with the three main stars of Andromeda, Alpheratz, Mirach and Almach, leading off from its top-left corner. The Andromeda Galaxy, M31, could hardly be better placed, being visible to the naked eye in a decent sky and not difficult at all through binoculars. It stands 2.5 million light years (ly) away and appears as an oval smudge some 8° above Mirach.
A line through the Square’s two right-hand stars points the way to Fomalhaut, bright but very low in the south. I mentioned last time that it may have at least a couple of planets. In fact, the first so-called extrasolar planet circling a solar-type star was discovered in 1995 and is about half the size of Jupiter yet orbits in only 4.2 days at a distance only one seventh of that of Mercury from the Sun. The star concerned is 51 Pegasi, magnitude 5.5 and 50 ly distant, which is unmistakable through binoculars just 1.5° or 3 Moon-widths to the right of the Scheat-Markab line.
Of the 1,800-plus extrasolar planets now known, no less than four orbit Upsilon Andromedae, a fourth magnitude star at 44 ly that stands between Mirach and Almach (see chart).
Jupiter, is creeping eastwards to the right of the famous Sickle of Leo. Rising in the east-north-east at about 23:20 on the 1st and as early as 21:40 on the 30th, it is prominent until dawn as it climbs through our south-eastern sky to pass about 50° high on our meridian before dawn. The Jovian disk is 38 arcseconds across when Jupiter lies near the Moon on the night of 13/14th.
The annual Leonids meteor shower lasts from the 15th to the 20th, building to a sharp peak on the morning of the 18th. Its super-swift meteors flash in all parts of the sky, though their paths radiate from a point in the Sickle. There is little moonlight interference this year, but meteor rates may be well down on what they were a few years ago when the shower’s parent comet was in the vicinity.
Venus sets too soon after the Sun to be seen, and with Saturn reaching conjunction on the Sun’s far side on the 18th, our only other observable bright planet is Mercury, fortunately putting on its best morning show of 2014.
On the 1st Mercury rises two hours before the Sun and shines at magnitude -0.5 as it climbs to an altitude of 10° in the east-south-east forty minutes before sunrise. Although it soon brightens to magnitude 0.8, it also slips back towards the Sun, so that by the 14th it rises 89 minutes before the Sun and is 6° high forty minutes before sunrise. Given a clear horizon, though, binoculars should show it easily and it should be a naked-eye object until it is swamped by the brightening twilight. Look for Virgo’s leading star, Spica, climbing from below Mercury to pass 5° to its right on the 7th.