An invisible ‘Black Moon’ ghosts the sky in August plus Venus and Jupiter rise
together.
The Sun passes from Cancer (The Crab) on 10 August at 10:55 am and enters Leo
(The Lion) but comes closer by 854,171 km. We emerge from perpetual
astronomical twilight. Daylight shortens from 16:02 (16.038 hours) on 1 August
to 13:54 (13.893 hours) on 31 August so we gain 2 hours and 9 minutes of
night time, by the end of the month.
The Moon begins the month in Virgo (The Maiden) and ends in Ophiuchus (The
Serpent Bearer) but comes closer by 2,631 km. The first first quarter (sic) of
the new Lunar cycle shows up on 1 August at 1:41 pm in Virgo (The Maiden). The
first Lunar apogee (furthest from Earth) occurs on 1 August at 9:37 pm and
takes the Moon to 404,201 km away from Earth—around 19,801 km further than
average—subtending an angle of 29.6 arc-minutes. The full Sturgeon Moon makes
an appearance on 9 August at 8:55 am in Capricornus (The Sea Goat). Lunar
perigee (closest to Earth) on 14 August at 7:07 pm finds the Moon some 369,254
km away from Earth—around 15,146 km closer than average—subtending an angle
of 32.4 arc-minutes. The Moon enters last quarter on 16 August at 6:12 am in
Aries (The Ram). The new Moon appears on 23 August at 7:07 am in Leo (The Lion)
beginning a new synodic (Lunar) month which will last 29 days, 13 hours and 48
minutes. This is an astronomical ‘Black Moon’ being defined as the 3rd new moon
within the same astronomical season. The second Lunar apogee occurs on 29
August at 4:38 pm and takes the Moon to 404,585 km away from Earth—around
20,185 km further than average—subtending an angle of 29.5 arc-minutes.
Finally, the second first quarter (sic) of the new Lunar cycle shows up on 31
August at 7:25 am in Scorpius (The Scorpion).
For the inferior planets: Mercury begins the month in Cancer (The Crab) and
ends in Leo (The Lion) but recedes by 93,949,967 km and, contrarily, increases
in magnitude from 5.41 to -1.35 (509.25 times in brightness) over the month.
Mercury’s see-saw orbit sees it return to a prograde path from retrograde on 10
August and reach greatest western elongation on 19 August. The ‘Swift Planet’
closes out the month with another perihelion passage on 27 August. Meanwhile,
Venus begins the month in Gemini (The Twins) and ends in Cancer (The Crab) but
recedes by 28,990,238 km. Venus decreases in magnitude from -4.00 to -3.95
(1.05 times in brightness) over August. Between 6–18 August, Venus and Jupiter
will rise side-by-side around 3 am in Gemini (The Twins). The optimum day will
be 12 August when Venus will be 0.9 degrees south of Jupiter in the pre-dawn
hours.
For the superior planets: Mars remains in Virgo (The Maiden) all month but
recedes by 21,598,312 km and maintains a steady brightness of 1.6 magnitudes.
Jupiter remains in Gemini (The Twins) throughout August but comes closer by
43,919,235 km. The ‘Red Giant’ increases in magnitude from -1.92 to -1.99 (1.07
times in brightness) over the month. On 20 August, around 4:30 am, Jupiter,
Venus and the waning crescent Moon will form a triangle in the eastern sky.
Keen-eyed observers may also glimpse Mercury photo-bombing the event but much
nearer the horizon! Turn around, roughly 140 degrees in azimuth, and, there,
in Pisces (The Fishes) will be Saturn.
Saturn remains in Pisces (The Fishes) but comes closer by 45,899,569 km and so
increases in magnitude from 0.80 to 0.65 (1.15 times in brightness). Uranus
remains in Taurus (The Bull) but comes closer by 77,262,177 km. Uranus
maintains a brightness of 5.8 magnitudes and reaches western quadrature on 24
August. Neptune remains in Pisces (The Fishes) and comes closer by 46,820,627
km. Observing Neptune requires binoculars or a telescope but it will lurk very
close to Saturn all month. Our skymap shows how close they are in the south-east.
If you are still unsure of how to find the elusive ‘Blue Planet’, try using the
waning gibbous Moon on 13 August at 1:30 am to find Saturn: Neptune will then be
about 1 degree north.
The Perseid (007 PER) meteor shower is one of the most active of the year and
peak overnight on 12/13 August with up to 100 shooting stars per hour. The
radiant point is close to the principal star, Mirfak. This year, however, the
82% illuminated waning gibbous Moon will hamper observing. The parent comet is
109P/Swift-Tuttle discovered in 1862 but last seeding the meteor shower in
- In the Catholic church they are called the ‘Tears of Saint Lawrence’
because mourners first saw these shooting stars when carrying the saint’s body
(after he had been martyred by roasting over hot coals). 10 August is also the
saint’s feast day.
Within Perseus (The Hero) is the 3-solar radii star Algol—sometimes
unfavorably named the ‘Demon Star’—whose surface temperature is 12,500 Kelvin
lying at some 90 light years. It was discovered to be variable in 1667 but the
reason behind the variability was not explained until the late 19th century
when it was discovered to be the first ever eclipsing binary. The companion
star is slightly bigger but fainter and lies less than 10 million km away.
As these 2 stars rotate around their barycentre, they eclipse each other
with the larger occultation dimming the magnitude from 2.1 to 3.4 over a
10-hour period. This eclipse takes place every 2.867 days but the secondary
eclipse is too faint for the naked eye. Today, we know that Algol is actually a
triple star system but the third companion is much fainter and much further
away from the 2 principal components.
You may read about the newly discovered comet 3I/ATLAS (C/2025 N1) which is
designated as an ‘interstellar object’ (ISO). It is the fastest ISO ever
discovered and, being an interstellar object, it comes from another planetary
system inside our galaxy. By studying this comet in detail in the coming
months, astronomers will get a fix on the chemistry and physics in potential
exoplanet systems. Although it is moving fast, around 68 km/s, it will not come
anywhere near Earth but will fly-by tantalizingly close to Mars. It emanates
from Sagittarius (The Archer) and appears as if he has aimed a ‘free sample
return mission’ our way!
At the time of our sky map, some constellations visible are Cepheus (The King)
at zenith, Lynx (The Lynx) in the north, Andromeda (The Chained Maiden) in the
east, Corona Borealis (The Northern Crown) in the west (which contains our, so
far, elusive recurrent nova known as the Blaze star) and Microscopium (The
Microscope) in the south. The ecliptic hosts Taurus (The Bull), Aries (The
Ram), Pisces (The Fishes), Aquarius (The Water Bearer), Capricorn (The Sea
Goat) and Sagittarius (The Archer).
The ‘Summer Triangle’—Vega in Lyra (The Lyre), Altair in Aquila (The Eagle)
and Deneb in Cygnus (The Swan)—is prominent at high altitude in the south.
Also, highly visible in the east is the great square of Pegasus (The Winged
Horse) with the sentinel stars Scheat, Alpheratz, Algenib and Markab.
Circumpolar constellations—always above the horizon—include Camelopardalis
(The Giraffe), Cassiopeia (The Seated Queen), Draco (The Dragon) and Ursa Major
(The Great Bear).
