Mars shines brightly at opposition in Virgo
Six years have passed since Mars was as close and bright as it is this month, but two other planets outshine it and a fourth, Saturn, will soon be at its best for the year. There are also two of 2014’s four eclipses but, as with the second pair in October, neither is of much interest for observers in Scotland.
For the moment, our evening sky retains a flavour of stellar feast we enjoyed over the winter. Orion is still on show in the south-west at nightfall below the conspicuous planet Jupiter. Orion’s Belt now lies almost parallel to the horizon, a line along it pointing to the left towards Sirius, our brightest nighttime star, and to the right towards Aldebaran and the Pleiades in Taurus. By our star map times, though, Orion has all but sunk below our western horizon.
Jupiter, however, continues as our brightest evening object bar the Moon. As it slips 3.5° or seven Moon-widths eastwards in the middle of Gemini during April, it fades a little between magnitude -2.2 and -2.0 and its telescopic diameter shrinks from 38 to 35 arcseconds. The earlier in the night that we catch it, the higher it stands and the sharper the view of its cloud-banded disk. By our map times Jupiter is some 30° high in the west and on its way to setting in the north-west four hours later.
The month begins with impressive views of the young earthlit Moon in the west at nightfall. It is only 5% illuminated on the 1st as it stands 14° high forty minutes after sunset. Look for it below the Pleiades on the 2nd, below the Aldebaran-Pleiades line on the 3rd and 6° below Jupiter on the 6th as it nears first quarter.
Mars reaches opposition on the 8th when it lies 93 million km away and shines at magnitude -1.5 so that its orange-red beacon rivals Sirius in brightness if not in colour. By definition, it stands opposite the Sun in the sky so that we find it climbing from the eastern horizon as the evening twilight fades to pass 28° high on Edinburgh’s meridian two hours after our map times. As the arrow on our south map shows, Mars tracks 10° westwards in Virgo during April, from 5° above the magnitude 1.0 Spica today to lie 1.6° below-left of the famous binary star Porrima as the month ends.
Often the day of opposition is when a planet is closest to us but Mars is approaching the Sun in its orbit and is 450,000 km closer to us on the 14th than on the 8th. Through a telescope, its ochre disk is 15 arcseconds wide and shows dusky markings and the dwindling white smudge of its north polar ice cap, tipped about 22° towards us.
The full Moon lies below Mars on the evening of the 14th and is approaching Spica as it sets for Edinburgh at 06:08 BST on the 15th. Only 14 minutes before this, and while it is less than 2° above the west-south-western horizon in the twilight, it begins to enter the outer shadow of the Earth, the penumbra. Sadly, we have no hope of seeing any dimming of the lunar disk before it sets. Observers in the Americas are much better placed to view the resulting total eclipse of the Moon which is total from 08:07 until 09:26 BST (03:07 to 04:25 EDT).
Sunrise/sunset times for Edinburgh change from 06:44/19:51 BST on the 1st to 05:32/20:50 on the 30th while the duration of nautical twilight at dawn and dusk stretches from 84 to 105 minutes. After first quarter on the 7th, the Moon is full during the eclipse on the 15th, at last quarter on the 22nd and new on the 29th when a small area of Antarctica and perhaps a few penguins experience an annular eclipse of the Sun. A partial solar eclipse is visible from Australia and the southern Indian Ocean.
On course to reach opposition in May, Saturn rises at Edinburgh’s east-south-eastern horizon at 23:31 on the 1st and only 36 minutes after sunset by the 30th, climbing to pass 18° high on the meridian four hours after our map times. Improving from magnitude 0.3 to 0.1, it edges westwards in Libra and draws ever closer to the Moon overnight on the 16th-17th when Saturn’s disk is 18 arcseconds wide while its stunning rings span 42 arcseconds.
Mercury is hidden in the dawn twilight until it passes around the Sun’s far side on the 26th. Venus, brilliant as a morning star, rises in the east-south-east seventy minutes before sunrise on the 1st and in the east only 51 minutes before the Sun on the 30th. Dimming from magnitude -4.3 to -4.1, its gibbous disk shrinks from 22 to 17 arcseconds in diameter.
It is less than a month since results from NASA’s WISE spacecraft appeared to rule out any Jupiter or Saturn-sized planet lurking unseen in the outermost solar system. Now we learn that a new dwarf planet, dubbed 2012 VP113, has been found to have an orbit that comes no closer to the Sun than 80 times the Earth’s distance, further than any other known object in the solar system. Thought to be a ball of rock and ice perhaps 450 km wide, it may be six times further away at its farthest, and take perhaps 5,000 years to complete each orbit.
Surprisingly, 2012 VP113’s orbit is similarly orientated to those of some other remote bodies, including the only other comparable object, Sedna. There is speculation that this is because they are influenced by a larger undiscovered world, perhaps a super-Earth, even further out.