The astronomical sky over Edinburgh this month
August witnesses a rare Blue Super Moon, the first of four consecutive supermoons, and the glorious Perseid meteor shower.
The Sun leaves Cancer (The Crab) on 10 August at 5:11 am and enters Leo (The Lion). Daylight
shortens from 16:01 (16.023 hours) on 1 August to 13:53 (13.876 hours) on 31 August so we gain
a whopping 2 hours and 9 minutes of night time, by month’s end. Summer’s perpetual twilight
ends on 8 August and we will enjoy darker astronomical skies until next June!
The new Moon appears on 4 August at 12:13 pm in Cancer (The Crab) beginning a new synodic
(Lunar) month. Lunar apogee (furthest from Earth) occurs on 9 August at 2:39 am and takes the
Moon to 405,328 km away from Earth – around 20,928 km further than average – subtending an
angle of 29.5 arc-minutes. The first quarter of the new cycle shows up on 12 August at 4:19 pm
in Libra (The Scales). The full Sturgeon Moon makes an appearance on 19 August at 7:26 pm in
Aquarius (The Water Bearer). Lunar perigee (closest to Earth) on 21 August at 6:10 am finds
the Moon some 360,184 km away from Earth – around 24,216 km closer than average – subtending
an angle of 33.2 arc-minutes. Finally, the Moon enters last quarter on 26 August at 10:26 am
in Taurus (The Bull).
A further word about the August full Moon: it is an astronomical Blue Moon. The summer
(astronomical) season exists between the summer solstice, on 20 June, and autumnal equinox on
22 September. This period of 93.66 days contains 4 full Moons on 22 June, 21 July, 19 August
and 18 September. In such circumstances, the 3rd full Moon of the 4 full Moons within the same
season is known as a Blue Moon. Note that the lay definition of a Blue Moon – two full Moons
within the same calendar month – does not apply here.
We are not finished, however, as the August full Blue Moon also qualifies as a supermoon, the
first of 4 consecutive supermoons. A supermoon occurs when the Moon is full or new and close
to perigee and is technically referred to as a perigee syzygy. When at apogee syzygy, it is
called a micromoon. http://astropixels.com/ephemeris/moon/fullperigee2001.html provided by
Fred Espernak is a good source. So, we can see that the August full moon can be described as
the Sturgeon Blue Super Moon.
For the inferior planets: Mercury appears to wobble on the sky by changing direction twice but
this is only an artifact of astronomical geometry. Since it reaches inferior conjunction (in
front of the Sun when viewed from Earth), it is impossible to see but it emerges as a morning
object after 28 August very low in the east. We fare slightly better with Venus as an evening
object, setting 30 minutes or so after the Sun, all month. Steady at -3.8 magnitudes, it
starts August at 1.64 AU and ends the month at 1.52 AU, some 18 million km closer. It will
conjunct with Regulus in Leo (The Lion) before setting on 4 August and will be joined by the
waxing crescent Moon the following night. All will be close to the western horizon, though.
For the superior planets: both Mars and Jupiter remain in Taurus (The Bull) and are improving
morning planets, rising after 1 am or so. They form an interesting triangle with Aldebaran on
4 August when Mars will be 4.9 degrees north of Taurus’ brightest star in the wee hours. In
fact, Mars and Aldebaran (the Bull’s eye) will be almost equal in brightness at 0.9 magnitude
and both have a reddish hue so make sure you can tell them apart! Over the next 10 days, they
will get closer in the sky. By 14 August, Jupiter (-2.0 mag) and Mars (0.84 mag) will be
within 0.3 degrees of each other with Jupiter outshining Mars by some 14 times.
Saturn rises well after sunset and rises higher as the month progresses. On 21 August around 4 am,
the waning gibbous Moon will occult (pass in front of) Saturn and it will be lost to view for the
remainder of the night. Since the Moon will be 93 per cent illuminated, it will far outshine Saturn
so this event will be difficult to see.
Uranus, also in Taurus (The Bull), comes closer to Earth by some 78 million km. It reaches
western quadrature on 19 August when the angle between Sun, Earth and planet will be an exact
right angle. It is an improving morning planet all month and lurks near the Pleiades (M45)
open cluster of bright stars. When it rises on 25 August, it will be roughly half a degree
below the waning gibbous Moon but the said Moon will be 52 per cent illuminated. Neptune, always
requiring optical assistance to see, will peak in altitude, due south, from mid-month.
The Perseid meteor shower is one of the brightest and best of the year which run from 17 July
though 24 August. They peak around 9 – 13 August and the optimum night for observation in
Edinburgh and Lothian will be 12/13 August. These meteors are radiant from Perseus (The Hero)
near the principal star Mirfak (shown on our sky map). They should produce up to 100 meteors
per hour and visibility is excellent since the Moon sets at 10:36 pm. The parent comet is
109P/Swift-Tuttle discovered in 1862. In Roman Catholic lore they are known as the ‘Tears of
Saint Lawrence’ because mourners first saw the meteor shower when carrying the saint’s body
after being martyred by roasting over hot coals. 10 August is also the saint’s feast day.
On 31 August the Aurigid meteor shower peaks with, perhaps, 10 shooting stars per hour. The
waning crescent Moon sets early at 7:55 pm allowing excellent visibility. The parent comet is
C/1911 N1 Kiess. Although Auriga (The Charioteer) is at low altitude, the bright star Capella
may help with finding the radiant point.
Comet 13P/Olbers starts August at 287 million km from Earth at magnitude 8.0 making it a
telescope or binocular object only. It will be in Ursa Major (The Great Bear), one of the
easiest constellations to spot. On 11 August, it moves into Coma Berenices (Berenice’s Hair)
at 293 million km from Earth and dims to 8.3 magnitudes. Thereafter, it loses altitude for the
rest of the month and ends up unobservable at 9.2 magnitudes and 318 million km from Earth.
We are fortunate that the Blaze Star (T CrB) has not yet erupted as a recurrent nova during
the summer months when visibility would have been poor. So we continue to monitor Corona
Borealis (The Northern Crown) for this very rare event which is expected to occur sometime
before year’s end.
At the time of our sky map, some constellations visible are Draco (The Dragon) at zenith,
Camelopardalis (The Giraffe) in the north, Cygnus (The Swan) in the east, Bootes (The
Herdsman) in the west, and Ophiuchus (The Serpent Bearer) in the south. The ecliptic hosts
Aquarius (The Water Bearer), Capricornus (The Sea Goat), Sagittarius (The Archer), Scorpius
(The Scorpion), Libra (The Scales), Virgo (The Maiden), and Leo (The Lion).
The ‘Summer Triangle’ – Vega in Lyra (The Lyre), Altair in Aquila (The Eagle) and Deneb in
Cygnus (The Swan) – is prominent high in the south-east. Below the summer triangle is the
small constellation of Delphinus (The Dolphin). The two brightest stars are Sualocin
(alpha-Dephini) and Rotanev (beta-Delphini). Odd names, you might think, until your read them
backwards and they spell out Nicolaus Venator. This is the Latin version of the Italian name
Niccolo Cacciatore (Nicholas Hunter) who was the director of Palermo Observatory in 1814 when
the stars were first included in their atlas of the heavens! Who says astronomers have no
sense of humour?
Circumpolar constellations—always above the horizon—include Cassiopeia (The Seated Queen),
Cepheus (The King) and Ursa Major (The Great Bear).
