The Earth reaches the furthest point from the Sun all year and we still anticipate the eruption of the Blaze Star in Corona Borealis (The Northern Crown).
Aphelion is the term used for when the Earth and Sun are furthest apart and occurs on 5 July at 6:16 am
when the Earth will be 152,099,962 km away from the Sun. This is 4,999,330 km further than perihelion
(closest to the Sun) last January. To put it in terrestrial terms, if you were driving your car at a
zippy 100 km/h, it would take you 5.7 years travelling 24/7 to cover the extra 3.13 million miles!
The Sun passes from Gemini (The Twins) on 20 July at 6:07 am and enters Cancer (The Crab). The good news
is that we are getting longer nights now that the Solstice has passed. Daylight shortens from 17:29 (17.487
hours) on 1 July to 16:05 (16.087 hours) on 31 July so we gain 1 hour and 24 minutes of night time,
by the end of the month. The bad news is that we are still within the summer months of perpetual twilight,
so reducing astronomical visibility to the brightest objects in the sky. The Sun, however, is reaching
‘Solar Max’ which is the peak of the 11 year Sun spot cycle. This, coupled with the recent solar flares,
should herald better aurorae between now and the end of the year.
The new Moon appears on 5 July at 11:57 pm in Gemini (The Twins) beginning a new synodic (Lunar) month.
Lunar apogee (furthest from Earth) occurs on 12 July at 9:15 am and takes the Moon to
404,400 km away from Earth—around 20,000 km further than average—subtending an angle of 29.5 arc-minutes.
The first quarter of the new cycle shows up on 13 July at 11:49 pm in Virgo (The Maiden).
The full Buck Moon makes an appearance on 21 July at 11:17 am in Capricornus (The Sea Goat). This is also known as
the Thunder Moon. Lunar perigee (closest to Earth) on 24 July at 6:50 am finds the Moon some
364,895 km away from Earth—around 19,505 km closer than average—subtending an angle of 32.7 arc-minutes.
Finally, the Moon enters last quarter on 28 July at 3:52 am in Aries (The Ram).
For the inferior planets: Mercury reaches greatest eastern elongation, at 26.9 degrees, on 22 July at 7:40 am.
On 27 July at 4:34 pm it reaches aphelion at 70 million km. Since it never reaches more than 7 degrees above the
horizon after sunset, it is difficult to observe. Venus is still lost in the Sun’s glare but reaches perihelion
at 107.5 million km on 10 July at 6:20 am.
Around 3:30 am throughout July, all the superior planets should be viewable. It helps that they all get closer to
Earth over the month with the consequent increase in brightness. On 15 July, around 3:30 am, Mars at 1.1 mag will
conjunct with Uranus at 5.8 mag being separated by less than 1 degree. Jupiter—around -2.0 mag—conjuncts with
the waning crescent Moon at 5 degrees separation on 3 July after 3:30 am in Taurus (The Bull). It does so again when
it rises, around 1 am, on 31 July. Saturn conjuncts on 25 July, after rising at 11 pm, with the waning gibbous Moon
which will be less than half a degree away.
We should take this moment to herald the re-awakening of Voyager I. Launched on 5 September 1977, Voyager I is now
in interstellar space and holds the record as the furthest man-made object in the cosmos. At 15 billion miles from
Earth it takes almost a day to send data back to us. Some science highlights include: discovery of Jovian rings, 2
new Jovian moons, Saturn’s multi-banded ring system (including B-ring spokes), 5 new Saturnian moons and Titan’s
Earth-like (nitrogen rich) atmosphere. Perhaps, though, the most significant contribution to human culture from
Voyager I is the image known as the ‘Pale Blue Dot’: a family snapshot taken as it left the outer Solar system in 1990.
After a computer glitch caused a hiatus of several months in data streaming, NASA scientists fixed
the spacecraft and it is now returning data from interstellar space. We might expect to collect data from this remarkable
spacecraft until the 2030s!
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 peak on 10 July are radiant from Pegasus (The Winged Horse) near the star Markab (alpha Pegasi).
Only 5 meteors per hour are expected. The parent body is thought to be comet C/1979 Y1 (Bradfield).
On 28 July, we have the gamma Draconids radiant from Draco (The Dragon) near the star Rastaban (beta Draconis).
The parent body is unknown.
On 31 July, we have the southern delta Aquariids, 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 comet may be 96P/Machholz.
Also on 31 July, we have the alpha Capricornids radiant near the horns of the sea goat.
Discovered in 1871, the parent comet is 169P/NEAT but the Earth won’t pass through the main cometary
debris for another 2 centuries!
Comet 13P/Olbers begins July at 7.5 mag in Lynx (The Lynx) and ends the month at 8 mag in Ursa Major (The Great Bear).
It will reach the closest approach to Earth on 20 July at 284 million km. This Halley-like comet has a period of 69
years and was last visible in 1956 but you will be lucky, even with binoculars or a telescope, to catch it this time around.
The recurrent nova called the Blaze Star (T CrB) is expected to pop sometime before the end of the year.
We eagerly anticipate this once in a lifetime event but, of course, would prefer it later in the year and,
certainly, outside the summer’s perpetual twilit sky! Vigilant observers should continue to monitor the sky
near CrB epsilon-13 to see if the 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, Cygnus (The Swan) in the east,
Leo (The Lion) in the west, and Ophiuchus (The Serpent Bearer) in the south.
The ecliptic hosts Sagittarius (The Archer), Scorpius (The Scorpion), Libra (The Scales),
Virgo (The Maiden), and Leo (The Lion).
Around mid-July, after sunset and into the wee hours, look south for the tail of Scorpius (The Scorpion) featuring the red
super-giant star Antares and the M4 cluster of more than 1000 stars.
The ‘Summer Triangle’—Vega in Lyra (The Lyre), Altair in Aquila (The Eagle)
and Deneb in Cygnus (The Swan)—is prominent in the 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
prominent in the south-west.
Circumpolar constellations—always above the horizon—include Cassiopeia (The Seated Queen),
Cepheus (The King) and Ursa Major (The Great Bear).
Phil Daly is a former employee of the Royal Observatory Edinburgh (now UKATC) on Blackford Hill.
He has worked on the UK's overseas telescopes in Hawaii (UKIRT, JCMT) and on large telescopes
at major astronomical observatories worldwide. He is currently part of an international collaboration
searching for optical counterparts to gravity wave events using multi-messenger astronomy.
