The Great American Eclipse
Jupiter aids last chance to spot Comet Ponsbrooks, says Alan Pickup
The Moon’s shadow races across North America on the 8th in what is being called the Great American Eclipse. Observers along a track that stretches from northern Mexico to Newfoundland, taking in the cities of Austin, Dallas, Indianapolis, Cleveland and Montreal, enjoy the spectacle of a total solar eclipse.
The rest of Central and North America, bar Alaska, sees a partial eclipse but here even a sliver of the brilliant solar surface is enough to deny views of the prominences and the solar corona that are visible during totality.
The partial eclipse also takes in much of the eastern Pacific and the North Atlantic and just makes it as far as Scotland, Wales and Ireland. Here, though, we must be content with the briefest partial eclipse just prior to sunset, so we need an open outlook to the west-north-western horizon and a lot of luck to see anything.
Remember that we must never view the Sun directly through binoculars or a telescope. To do so invites serious and permanent eye damage.
We may project the Sun’s light through a small telescope, or one side of the binoculars, onto a white card held away from the eyepiece, or fit our instrument with safe and certified solar filters which are available online.
From Edinburgh, the Moon’s edge begins to be seen at the bottom of the Sun’s disk at 19:54 BST when the Sun is only one degree high. The Moon hides 14% of the Sun’s diameter only 8 minutes later at 20:02 as that part of the Sun slips below the horizon.
Circumstances are slightly better the further west we go. Glasgow sees 21% coverage until 20:06, while from Stornoway up to 34% of the Sun is hidden until 20:20.
If Scotland it too far east on the Earth for the best of this eclipse, we are also too far north to see much of the planets during April.
Mercury was at its best as an evening star earlier in March but dives around the Sun’s near side and through inferior conjunction on the 12th. Thereafter it joins Venus, Mars and Saturn to the west and south of the Sun, where we are unlikely to spot them in the bright predawn twilight. All are more easily seen from the southern hemisphere.
This leaves Jupiter as our only conspicuous planet, though this too will be lost from view as it sinks lower in the west with each evening and disappears into the twilight at the month’s end. As seen from Edinburgh, its altitude one hour after sunset drops from 19° on the 1st to only 1° on the 30th. The giant planet tracks 7° east-northeastwards against the stars, crossing from Aries into Taurus on the 28th.
One of its parting acts is to have a spectacular conjunction with the young earthlit Moon on the evening of the 10th.
Look for them low in the west-northwest
as the twilight fades, with the Moon only 6% illuminated and 3° or six Moonbreadths above and to the right of the planet. Jupiter shines at magnitude -2.0, brighter than any star, and shows a 34 arcsecond disk through a telescope, though the “seeing” will be poor because of its low altitude.
Comet 12P/pons-brooks has been sinking lower but brightening in our western evening sky over recent weeks and is now probably just visible to the naked eye, but an easier object to spot through binoculars. Fortunately, we now have Jupiter as a guide to its location.
On the evening of the 1st, the comet lies 13° to the right of Jupiter and only 1.6° to the left of the bright star Hamal in Aries. Its tail is impressive in photographs and will be pointing up and to the left from the comet’s fuzzy head. Pons-brooks passes 3° below Jupiter on the evening of the 13th but by then it may be a difficult catch in our western twilight.
The comet’s 71-year orbit brings it to perihelion, 117 million km from the Sun, on the 21st and, at least from Scotland, we won’t see it again for a lifetime.
Jupiter has another conjunction on the 20th when it passes only 0.5° south of the planet binocular-brightness (magnitude 5.8) Uranus, an encounter which occurs every 14 years.
Edinburgh’s sunrise/sunset times change from 06:42/19:52 BST on the 1st to 05:30/20:51 on the 30th. The Moon’s last quarter on the 2nd is followed by new during the eclipse on the 8th, first quarter on
the 15th and full phase on the 24th.
Regulus in Leo, the brightest star in the south-western sky at our map times, is a little fainter than Spica in Virgo, lower in the south-south-east. Even brighter and higher is Arcturus in Bootes in the southeast and found by following the curve of the Plough’s handle down from the zenith.
The Virgo Cluster, plotted between Denebola in Leo and Vindemiatrix in Virgo, comprises 1,300 or more galaxies in a swarm centred 54 million light years away.
The brightest are around the tenth magnitude and therefore need a telescope, but they include the supergiant elliptical galaxy M87, whose black hole became the first to be imaged in 2021.
Alphard is the leading star in the long winding constellation of Hydra the Water Snake. It lies 23° directly below Regulus at our map times and is sometimes called the Solitary One since it has few comparable stars nearby. Tycho Brahe, perhaps the greatest observational astronomer of pre-telescopic days, called it Cor Hydrae for the “Heart of Hydra”.
Tycho was an eccentric and aristocratic 16th-century Dane who lost part of his nose in a duel. He used a range of sighting instruments that included sextants, but it is probably coincidental that the constellation of Sextans the Sextant was placed adjacent to Alphard when it was introduced in 1687.
Its stars are below the usual brightness cut-off for our charts, but this month I’ve made an exception.