The Earth reaches the furthest point from the Sun all year and 3 planets appear to reverse orbit.
As many readers will have seen, a new astronomical research facility came
online in the past few months: the Vera Rubin Observatory which hosts the Large
Synoptic Survey Telescope. Your present interlocutor had a (very) small part in
the design process. The telescope is designed to automatically image the
northern sky over the next decade. It will utilize the large 3.2 GigaPixel
camera footprint—equivalent to 7 full moons across—to visit each 10 square
degree tile 825 times on average. This means that any transient phenomena
should be picked up by the data pipelines. Of particular interest are near
Earth objects (NEOs and potential Earth impactors) and supernova that will
probe the dark energy content of the universe. You can explore these new images
(and more to come) via https://rubinobservatory.org/ or using their web
application at https://skyviewer.app/.
Aphelion is the term used for when a planet and Sun are furthest apart and, for
Earth, this occurs on 3 July at 9:04 pm when the Earth will be 152,087,735 km
away from the Sun. Over the whole of July, though, the Sun comes closer to
Earth by 248,314 km.
The Sun passes from Gemini (The Twins) on 20 July at 11:51 am and enters Cancer
(The Crab). We are getting longer nights now that the Solstice has passed.
Daylight shortens from 17:30 (17.493 hours) on 1 July to 16:06 (16.102 hours)
on 31 July so we gain 1 hour and 23 minutes of night time, by the end of the
month. We are still within the summer months of perpetual twilight, though, so
reducing astronomical visibility to the brightest objects in the sky. The Sun,
however, is still close to ‘Solar Max’ which is the peak of the 11 year Sun
spot cycle. This may herald better aurorae between now and the end of the year.
The Moon begins the month in Leo (The Lion) and ends in Virgo (The Maiden). The
first quarter of the new Lunar cycle shows up on 2 July at 8:30 pm in Virgo
(The Maiden). Lunar apogee (furthest from Earth) occurs on 5 July at 3:26 am
and takes the Moon to 404,662 km away from Earth—around 20,262 km further
than average—subtending an angle of 29.5 arc-minutes. The full Buck Moon
makes an appearance on 10 July at 9:37 pm in Sagittarius (The Archer). This is
also known as the Thunder Moon. The Moon enters last quarter on 18 July at 1:38
am in Pisces (The Fishes). Lunar perigee (closest to Earth) on 20 July at 2:48
pm finds the Moon some 368,012 km away from Earth—around 16,388 km closer
than average—subtending an angle of 32.5 arc-minutes. Finally, the new Moon
appears on 24 July at 8:11 pm in Cancer (The Crab) beginning a new synodic
(Lunar) month which will last 29 days, 10 hours and 55 minutes.
For the inferior planets: Mercury remains in Cancer (The Crab) all month but
comes closer by 43,342,913 km. The ‘Swift Planet’ decreases in magnitude from
0.40 to 5.41 (101.23 times in brightness) over the month. Mercury reaches
greatest eastern elongation (from the Sun) on America’s Independence Day and
aphelion (furthest from the Sun) on 14 July. On 17 July, Mercury appears—at
least on sky—to reverse orbit to retrograde. From then on, Mercury approaches
Earth coming closest on 28 July but is lost for observing by 31 July when it
reaches inferior conjunction. After this time is transitions from an evening
planet to a morning planet. Venus begins the month in Taurus (The Bull) and
ends in Gemini (The Twins) but recedes by 33,872,820 km. The ‘Morning Star’
planet decreases in magnitude from -4.14 to -4.00 (1.14 times in brightness)
over the month.
For the superior planets: Mars begins the month in Leo (The Lion) and ends in
Virgo (The Maiden) but recedes by 28,884,201 km. The ‘Red Planet’ decreases in
magnitude from 1.49 to 1.60 (1.11 times in brightness) over the month. Mars
visits the Moon on the evening of 28 July passing 1.3 degrees north of the waxing
crescent Moon. Jupiter remains in Gemini (The Twins) all month but comes closer
by 18,057,658 km. This does not alter the brightness much which remains steady
at -1.75 magnitudes. The ‘Gas Giant’ is emerging from (solar) conjunction last
month becoming visible just before sunrise. In fact, on 23 July, in the
pre-dawn hours, Jupiter will be 4.9 degrees south of the waning crescent Moon.
Saturn remains in Pisces (The Fishes) all month but comes closer by 70,506,621
km. Saturn increases in magnitude from 0.96 to 0.80 (1.16 times in brightness)
over the month. The ‘Ringed Planet’—still appearing ringless until November
or so!—crosses to a retrograde orbit on 14 July. You may catch a glimpse of
Saturn during civil twilight on 16 July. Uranus remains in Taurus (The Bull)
all month but comes closer by 62,919,841 km. Neptune remains in Pisces (The
Fishes) all month but comes closer by 71,422,081 km. Neptune increases in
magnitude from 7.76 to 7.71 (1.05 times in brightness) over the month. The
‘Blue Giant’ also crosses to retrograde on 5 July.
There are four meteor showers in July but visibility is nigh on impossible
either due to twilight, Moon illumination, latitude or shooting star rates but
we mention them for completeness. The July Pegasids (175 JPE) peak on 10 July
and are radiant from Pegasus (The Winged Horse) near the star Markab. Only 3
meteors per hour are expected during a full Moon. The parent body is thought to
be comet C/1979 Y1 (Bradfield). We fare slightly better with the other 3
showers which occur between new Moon and first quarter. On 28 July, we have the
Gamma Draconids (184 GDR) radiant from Draco (The Dragon) near the star
Rastaban. The parent body is unknown but the ZHR is a lowly 5. Overnight on
30/31 July, we have the southern Delta Aquariids (005 SDA), radiant from
Aquarius (The Water Bearer) near it’s namesake star. There may be up to 25
meteors per hour but, as the name implies, viewing is much better at southern
latitudes. The parent body is thought to be comet 96P/Machholz. Also on 31
July, we have the Alpha Capricornids (001 CAP) radiant near the horns of the
sea goat. The ZHR is, again, low at 5. Discovered in 1871, the parent comet is
169P/NEAT but the Earth won’t pass through the main cometary debris for another
2 centuries!
Although both amateurs and professionals eagerly anticipate the recurrent nova
known as the Blaze Star, we would prefer it to be later in the year and,
certainly, outside summer’s perpetual twilit sky! Vigilant observers should
continue to monitor the sky near CrB epsilon-13 to see if Corona Borealis
(The Northern Crown) gains another jewel. Alphecca (sometimes called Gemma or
alpha-CrB) is the brightest star in the constellation, at 2.2 mag, and should
guide you to this transient event.
At the time of our sky map, some constellations visible are Draco (The Dragon)
at zenith, Camelopardalis (The Giraffe) in the north, Pegasus (The Winged
Horse) in the east, Coma Berenices (Berenice’s Hair) in the west, and Serpens
Cauda (The Serpent’s Tail) in the south. The ecliptic hosts Pisces (The
Fishes), Aquarius (The Water Bearer), Capricorn (The Sea Goat), Sagittarius
(the Archer), Scorpio (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 at mid-to-high altitude in the
south-east. The ‘Diamond of Virgo’—Arcturus in Bootes (The Herdsman), Cor
Caroli in Canes Venatici (The Hunting Dogs), Denebola in Leo (The Lion) and
Spica in Virgo (The Maiden)—is low in the west.
Circumpolar constellations—always above the horizon—include Cassiopeia (The
Seated Queen), Cepheus (The King) and Ursa Major (The Great Bear).
