Perseids back in force as Mars and Jupiter clash before dawn
Author: Alan Pickup
The maps show the sky at midnight BST on the 1st, 23:00 on the 16th and 22:00 on the 31st.
As darkness returns to the middle of our nights, so do the spectacular meteors of the Perseids shower, probably the most reliable of our annual displays. The month’s other highlights include an impressively close conjunction between Mars and Jupiter on the 14th and an occultation of Saturn by the Moon a week later.
The Summer Triangle, formed by the bright stars Vega in Lyra, Altair in Aquila and Deneb in Cygnus, stands high on the meridian on our star maps. The only two stars that rival these three at the map times are Arcturus in Bootes, much lower as it sinks in the west, and Capella in Auriga which is beginning its climb in the north-north-east. Above and to the right of Capella are the constellations of Perseus and Cassiopeia and between these we have the radiant point for the Perseids shower.
Perseid fireball 2022-0-02 captured by an ASE meteor camera, leaving a changing trail
This point marks the direction in space from which the Perseid meteoroids, debris from Comet Swift-Tuttle, are travelling as they disintegrate in the Earth’s upper atmosphere at 59 km per second. The resulting meteors are seen in all parts of the sky, with the brighter ones leaving glowing “trains” in their wake.
We encounter the Perseids stream between about 17 July and 24 August but we expect to hit its densest part on the afternoon of the 12th, making our best nights probably the 11-12th and 12-13th. The radiant climbs through the north-east after nightfall to stand very high in the east before dawn, so meteor rates should be higher later in the night. Under ideal dark conditions, an observer might count more than 80 Perseids per hour, but most of us would be thrilled to glimpse even half this number. Fortunately, the near-first-quarter Moon sets before it is properly dark, so moonlight hardly matters this year.
Edinburgh’s sunrise/sunset times change from 05:18/21:19 BST on the 1st to 06:16/20:09 on the 31st while the Moon is new on the 4th, at first quarter on the 12th, full on the 19th and at last quarter on the 26th.
With our night-long twilight gone until next summer, it is possible again to glimpse the Milky Way as it arches overhead at our map times from Sagittarius on the south-south-west horizon to Auriga in the north-north-east. On the way it flows through the Summer Triangle and close by Deneb.
I highlighted the Coathanger cluster, one third of the way from Altair to Vega in my July note, but our August spotlight falls on two planetary nebulae, so-called because these glowing disks or rings reminded early observers, most notably William Herschel, of the appearance of planets. Of course, they are not planets but the expanding shells of ionized gas ejected from dying red giant stars.
M27 Dumbbell Nebula by Mike Christie using ASERO-Murrell data
Perhaps the most famous is the Ring Nebula or Messier 57 (M57), between the two stars Sulafat and Sheliak (see chart) in Lyra. At magnitude 8.8 and a little over one arcminute wide, we certainly need a telescope for this. The Dumbbell Nebula or M27 measures 8 by 6 arcminutes and its magnitude 7.4 makes it easier to see through binoculars in a dark sky. The first planetary nebula to be discovered, we can find it 3° north of the brightest star in the small constellation of Sagitta the Arrow, 10° above Altair.
Saturn rises in the east during our evening twilight to become the brightest object low in the south-east at our map times. Edging westwards against the stars of Aquarius, it shows a flattened disk, 19 arcseconds wide, through a telescope. The rings span some 43 arcseconds and are inclined at only 2.5° towards us on the 1st, but at 3.5° by the 31st, and are the main reason why Saturn brightens a shade from magnitude 0.8 to 0.6 this month.
The just-gone-full Moon stands to Saturn’s right on the evening of the 20th, drawing closer overnight until the planet is occulted during our gathering morning twilight. Viewed from Edinburgh, Saturn sinks behind the Moon’s 1-o’clock position at 04:33 BST on the 21st, only to reappear near the 3-o’clock position at 05:10. Use a telescope to watch the slow disappearance and emergence of the planet and its rings and moons, the latter challenging because of our Moon’s glare and the twilight.
Look east before dawn on the 1st for the conspicuous planet Jupiter, magnitude -2.1, shining between the horns of Taurus. It lies some 16° to the right of the waning and earthlit crescent Moon and 7° below-left of Mars, one sixteenth as bright at magnitude 0.9. Mars, in turn, is 5° above the equally-bright Aldebaran and it is interesting to compare their reddish hues. That of Mars is due to the plentiful iron oxide, rust, in its soil while Aldebaran is a giant red-orange star with a surface some 1,800C cooler than that of our Sun.
Mars moves closer to Jupiter over the following days to stand only 24 arcminutes, less than a Moon’s breadth, above Jupiter on the 14th. Telescopes show Mars appearing only 6 arcseconds across on that morning, dwarfed by the 37 arcseconds of Jupiter’s cloud-banded disk. Of course, they are at very different distances, with Mars 229 million km away and Jupiter at 805 million km. Mars lies 23 arcminutes above-left of Jupiter on the 15th and its continuing easterly motion takes it to 8° below-left of Jupiter by the 31st. The Moon skims the southern edge of the Pleiades cluster on the morning of the 26th, stands above Jupiter on the 27th and is above-left of Mars on the 28th.
The other bright planets are poorly placed. Venus is brilliant at magnitude -3.9 but sets less than 40 minutes after Sun. Mercury passes through inferior conjunction on the Sun’s near side on the 19th and might be glimpsed low in the east before dawn at the month’s end. On the 31st it rises for Edinburgh at 04:44, and might be glimpsed through binoculars at magnitude 0.8 when it stands 4° high and 16° below-left of the impressively earthlit waning Moon one hour before sunrise.
Diary for 2024 August
Times are BST
- 3rd 01h Moon 1.8° S of Pollux
- 4th 12h New Moon
- 5th 23h Moon 1.7° N of Venus
- 5th 20h Mars 5° N of Aldebaran
- 10th 11h Moon 0.7° N of Spica
- 12th 15h Peak of Perseids meteor shower
- 12th 16h First quarter
- 14th 06h Moon within 0.01° of Antares
- 14th 18h Mars 0.3° N of Jupiter
- 19th 03h Mercury in inferior conjunction on near side of Sun
- 19th 19h Full Moon
- 21st 05h Saturn occulted by the Moon
- 26th 04h Moon brushes S of Pleiades star cluster
- 26th 10h Last quarter
- 27th 14h Moon 6° N of Jupiter
- 28th 01h Moon 5° N of Mars
- 30th 06h Moon 1.7° S of Pollux
- 31st 07h Moon 3° N of Praesepe star cluster
This is an extended version, with added diary, of Alan’s article published in The Scotsman on 31 July 2024, with thanks to the newspaper for permission to republish here.