Countdown to the Great American Eclipse
With two eclipses and a major meteor display, August is 2017’s most interesting month for sky-watchers. Admittedly, Scotland is on the fringe of visibility for both eclipses while the annual Perseids meteor shower suffers moonlight interference.
The undoubted highlight is the so-called Great American Eclipse on the 21st. This eclipse of the Sun is total along a path, no more than 115km wide, that sweeps across the USA from Oregon at 18:17 BST (10:17 PDT) to South Carolina at 19:48 BST (14:48 EDT) – the first such coast-to-coast eclipse for 99 years.
Totality is visible only from within this path as the Moon hides completely the dazzling solar surface, allowing ruddy flame-like prominences to be glimpsed at the solar limb and the pearly corona, the Sun’s outer atmosphere, to be admired at it reaches out into space. At its longest, though, totality lasts for only 2 minutes and 40 seconds so many of those people fiddling with their gadgets to take selfies and the like may be in danger of missing the spectacle altogether.
The surrounding area from which a partial eclipse is visible even extends as far as Scotland. From Edinburgh, this lasts from 19:38 to 20:18 BST but, at most, only the lower 2% of the Sun is hidden at 19:58 as it hangs a mere 4° high in the west. Need I add that the danger of eye damage means that we must never look directly at the Sun – instead project the Sun through a pinhole, binoculars or a small ‘scope, or use an appropriate filter or “eclipse glasses”.
A partial lunar eclipse occurs over the Indian Ocean on the 7th as the southern quarter of the Moon passes through the edge of the Earth’s central dark umbral shadow between 18:23 and 20:18 BST. By the time the Moon rises for Edinburgh at 20:57, it is on its way to leaving the lighter penumbral shadow and I doubt whether we will see any dimming, It exits the penumbra at 21:51.
Our charts show the two halves of the sky around midnight at present. In the north-west is the familiar shape of the Plough while the bright stars Deneb in Cygnus and Vega in Lyra lie to the south-east and south-west of the zenith respectively. These, together with Altair in Aquila in the middle of our southern sky, make up the Summer Triangle. The Milky Way flows through the Triangle as it arches overhead from the south-west to the north-east where Capella in Auriga rivals Vega in brightness.
Of course, many of us have to contend with light pollution which swamps all trace of the Milky Way and we are not helped by moonlight which peaks when the Moon is full on the 7th and only subsides as last quarter approaches on the 15th. New moon comes on the 21st and first quarter on the 29th. The Sun, meantime, slips another 8° southwards during the month as sunrise/sunset times for Edinburgh change from 05:17/21:20 BST on the 1st to 06:15/20:09 on the 31st.
Meteors of the annual Perseids shower, the tears of St Lawrence, are already arriving in low numbers. They stream away from a radiant point in the northern Perseus which stands in the north-east at our map times, between Capella and the W-pattern of Cassiopeia. We spot Perseids in all parts of the sky, though, and not just around Perseus.
Meteor numbers are expected to swell to a peak on the evening of the 12th when upwards of 80 per hour might be counted under ideal conditions. Even though moonlight will depress the numbers seen this time, we can expect the brighter ones still to impress as they disintegrate in the upper atmosphere at 59 km per second, many leaving glowing trains in their wake. The meteoroids concerned come from Comet Swift-Tuttle which last approached the Sun in 1992.
Although Neptune is dimly visible through binoculars at magnitude 7.8 some 2° east of the star Lambda Aquarii, the only naked-eye planet at our map times is Saturn. The latter shines at magnitude 0.3 to 0.4 low down in the south-west as it sinks to set less than two hours later. It is a little higher towards the south at nightfall, though, where it lies below-left of the Moon on the 2nd when a telescope shows its disk to be 18 arcseconds wide and its stunning wide-open rings to span 40 arcseconds. Saturn is near the Moon again on the 29th.
Jupiter is bright (magnitude -1.9 to -1.7) but very low in our western evening sky, its altitude one hour after sunset sinking from 6° on the 1st to only 1° by the month’s end as it disappears into the twilight. Catch it just below and right of the young Moon on the 25th.
Venus is brilliant at magnitude -4.0 in the east before dawn. Rising in the north-east a little after 02:00 BST at present, and an hour later by the 31st, it climbs to stand 25° high at sunrise. Viewed through a telescope, its disk shrinks from 15 to 12 arcseconds in diameter as it recedes from 172 million to 200 million km and its gibbous phase changes from 74% to 83% sunlit.
As Venus tracks eastwards through Gemini, it passes below-right of the star cluster M35 (use binoculars) on the 2nd and 3rd, stands above-left of the waning earthlit Moon on the 19th and around 10° below Castor and Pollux as it enters Cancer a few days later. On the 31st it stands 2° to the right of another cluster, M44, which is also known as Praesepe or the Beehive.
This is a slightly-revised version of Alan’s article published in The Scotsman on July 31st 2017, with thanks to the newspaper for permission to republish here.
We had a fantastic time at the Scottish Parliament this morning! A solar eclipse doesn’t come along all that often and it was great to share this one with members of the Society, local school children, members of staff and several hundred members of the public. My weather forecast from yesterday predicted 90% cloud cover, so I was delighted, when we set off at 7.00 am, that I had to put down the sun-visor in the car!
I gave a talk to school-children from James Gillespie’s High School and members of staff, while Seán talked to Holyrood Primary School children. The Parliament staff were brilliant! Everything was laid on for us and they had large plasma screens set up inside streaming live images from the Faroes and the BBC’s airborne ‘observatory’, so the children missed nothing.
Meanwhile outside, our band of around 14 volunteers manned the Society’s solar telescope, 6 ‘white-light’ telescopes, binoculars and a solar projection set up. As the crowds gathered, there was great excitement as the shadow bit into the Sun. Other members of the Society arrived during the morning to lend their support and enjoy the spectacle. Some cloud blew in as the maximum approached, but it didn’t dampen spirits at all.
The Parliament put together a video record of the morning – https://www.youtube.com/watch?v=f8rNj9S2G_4 – which very nicely summed up the general feeling of excitement and enjoyment of what was a truly memorable day.
Ken is the Society’s current President and also leads the Imaging Group. He can be seen being interviewed in the video above, explaining what made this such a special experience.
Our thanks go to the Scottish Parliament for hosting this event, and for all their assistance up to and during the event. Thank you as well to all the ASE members who came along to support this event – we couldn’t do this without you!
Comet Lovejoy heralds an exciting year in astronomy
The coming year promises to be an exciting one in astronomy and space research. NASA’s New Horizons mission is due to make the first flyby visit to Pluto in July while Comet Churyumov–Gerasimenko is nearest the Sun a month later, hopefully with Europe’s Rosetta probe still alongside and in prime position to observe the comet in full flow. Whether we hear again from the Philae lander remains to be seen, but its controllers are hopeful that it may come back to life in the spring.
Closer to home, the highlight is surely the solar eclipse on the morning of 20 March. This is total for the Faroe Islands and Svalbard while from Scotland the Moon hides all but a thin sliver around the Sun’s lower limb. From Edinburgh 94% of the Sun is obscured but for observers in Kirkwall, Lerwick and Stornoway this jumps to 97%.
January should be interesting in its own right. Not only are all the planets on view, but the constellations centred on Orion dominate our evening hours and we have the prospect that Comet Lovejoy may be a naked-eye object as it climbs to the right of Orion.
The year begins with the Quadrantids meteor shower which is active from the 1st to the 6th but reaches a rather sharp peak at around midnight on the 3rd/4th when as many as 80 medium-speed meteors per hour might be seen under ideal conditions from a dark location. Sadly, the Moon is full on the 5th so all but the brighter meteors will be swamped in the moonlight this year. Quadrantids appear in all parts of the sky but their paths trace back to a radiant point that is plotted low in the north at our star map times. Later in the night the radiant follows the Plough as it climbs through our north-eastern sky.
You may find it surprisingly that the Earth is at perihelion, our closest to the Sun, at 06:36 on the 4th. The centre of our planet then lies 147,096,204 km from the Sun, 5 million km closer than it does at aphelion on 6 July. Sunrise/sunset for Edinburgh change from 08:44/15:49 on the 1st to 08:10/16:43 on the 31st as the duration of nautical twilight at each dawn and dusk shrinks from 96 to 85 minutes. That full moon on the 5th is followed by last quarter on the 13th, new moon on the 20th and first quarter on the 27th.
As the Moon climbs in the east on the evening of the 1st, it stands below the Pleiades and above-right of Aldebaran, the eye of Taurus. By 19:00 the whole of Orion is unmistakable in the east-south-east, moving into the south-south-east by our map times as the Pleiades glimmer on the meridian.
Our chart traces the path of Comet Lovejoy as it climbs from Lepus the Hare, at Orion’s feet, through Eridanus the River and Taurus as it approaches the star Almach in Andromeda as the month ends. Discovered in August by the Australian amateur astronomer Terry Lovejoy, the comet has brightened more than most people expected and reached the threshold of naked-eye visibility, the sixth magnitude, in mid-December.
During January I expect it to shine at around the 4th or 5th magnitude, fainter than the stars on our chart but perhaps similar in brightness to the Orion Nebula. As such, it should be visible easily through binoculars as a hazy smudge, probably smaller than the Moon and with brighter core around its nucleus. Indeed, it should be a naked-eye object in a dark sky once the current moonlight has subsided. Photographs show a greenish hue and a narrow striated tail more than 5° long pointing up and to the left, away from the Sun.
Comet Lovejoy takes about 13,500 years to orbit the Sun and reaches perihelion on 30 January at a distance of 193 million km. It comes closest to the Earth, 70 million km, on the 7th.
Jupiter remains our pre-eminent planet as it rises in the east-north-east some 90 minutes before our map times. Blazing at magnitude -2.5 to -2.6, it is now creeping westwards to the west (right) of the Sickle of Leo and crosses the meridian in the early hours. A telescope shows it to be 44 arcseconds wide when it stands above the Moon on the morning of the 8th.
Venus is a brilliant magnitude -3.9 evening star very low in the south-west as the night begins. It sets for Edinburgh at 17:07 on the 1st and at 18:58 by the 31st. Use it (and binoculars) to locate Mercury which shines at magnitude -0.8 as it moves from 3° below-right of Venus on the 1st to lie less than 0.7° to the right of Venus on the 11th. It then tracks to the right of Venus and lies 7° away by the 22nd when it is a difficult magnitude 0.9 object in the twilight. On that evening, the thin earthlit Moon lies 9° above Venus and 7° to the right of the orange-hued planet Mars (magnitude 1.2) which otherwise remains the brightest object low in the south-west at nightfall.
The other naked-eye planet, Saturn, rises in the south-east at about 05:20 on the 1st and almost two hours earlier by the month’s end, becoming the brightest object low in the south-south-east to south before dawn. This month it tracks eastwards from Libra to pass 1° north of the star Graffias in Scorpius. Look for Saturn 2.6° below-left of the waning Moon on the 16th when a telescope shows its globe to be 16 arcseconds wide within rings that span 36 arcseconds and have their north face tipped 25° towards the Earth.