Astronomy Club of Asheville July 2018 Sky Events
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Astronomy Club of Asheville
July 2018 Sky Events
The Planets this Month – page 2
July 9th - Conjunction of Venus and Regulus – page 4
July 14th - Crescent Moon Meets Mercury and Venus – page 5
July 24th - Moon, Saturn and a Teapot – page 6
Planet Highlights – page 7
Moon Phases - page 9
July 6th - Earth Reaches Aphelion - page 10
July 2018 - All Eyes on Mars – page 12
July 27/28 - Delta Aquarid Meteors - page 15
www.AstroAsheville.org
Astronomy Club of Asheville
July 2018 Sky Events – the Planets
July 2018 reintroduces all five bright planets to evening skies, a sight not
seen for many months. Unfortunately, they aren’t visible simultaneously; a
few hours will be required to track down the quintet, which are spread
through a three hour window in the sky.
Quick moving Mercury is challenging to spot at the best of times. The solar
system’s innermost planet never wanders far from the Sun; the result is that
seeing Mercury often means hunting through dawn or dusk twilight. Start
with binoculars. Once located, keen eyes are usually able to resolve this
object without visual aid.
Find Mercury moving through the constellations Cancer and then Leo, low
to the western horizon, about 30 minutes after sunset. After the third week
in July the planet dims and quickly dives toward the Sun, lost now before
reappearing in morning skies at the end of August.
In contrast to elusive Mercury, extroverted Venus shouts out to all whose
eyes wander upward. Shining at magnitude –4.1, this beacon glows in the
west after sunset. Telescopes will reveal a waning gibbous phase, increasing
in diameter (and brightness) and moving through Leo as the month
progresses.
Astronomy Club of Asheville
July 2018 Sky Events – the Planets
Jupiter, high overhead near the meridian as darkness falls, remains in
excellent observing position this month. This dynamic gas behemoth is the
King of the Skies – even modest telescopes (and larger binoculars) will reveal
four Galilean moons and distinctive cloud bands spread across its disk. The
–2.2 magnitude planet is found meandering through Libra in July.
Saturn is now the property of evening skies, having reached opposition – its
closest approach of the year – at the end of June. Rising in the E-SE just after
sunset and found directly above the teapot’s “lid” in Sagittarius, it approaches
the meridian near midnight. July is still a fantastic month to enjoy Saturn’s
ring system; their northern face remains tilted near their maximum extant
(26°) toward the Earth.
While Jupiter may be the King of the Skies, July offers up some serious
competition – Mars – to Jupiter’s throne. This month the Red Planet makes
its nearest approach to the Earth since 2003 (see page 12). Not until 2035 will
Mars be as large or bright in our skies.
While the five bright planets grace evening skies, much dimmer Uranus and
Neptune are relegated to morning duty. Located in the water constellations
of Pisces and Aquarius, respectively, both can be observed before sunrise in
July.
Astronomy Club of Asheville
July 2018 Sky Events – the Planets
Conjunction of Venus and Regulus
On the evening of Monday, July 9th, catch an
appealing conjunction of the star Regulus and a
much brighter object – the planet Venus –
separated by 1 degree.
Look to the west about 9:30 p.m. EDT to locate
this pretty duo. Regulus, the alpha star in the
constellation Leo, forms the end of its famous
sickle asterism (also known as an “inverted
question mark”) and is about 77 light years
distant. Compare this to Venus’ relatively close
position at only 92 million miles!
A multiple star system, Regulus is an optical
binary star. Try your luck splitting this close pair
with binoculars while also enjoying brilliant
Venus. And with binoculars in hand, don’t forget
to attempt spotting Mercury, partially hidden by
Image courtesy of Sky & Telescope
twilight’s glow on the western horizon.
Astronomy Club of Asheville
July 2018 Sky Events – the Planets
A Crescent Moon Meets Mercury and Venus
On the evening of Saturday, July 14th, a
thin crescent Moon accompanies Mercury
in the fading glow of sunset. On the following
night, Sunday the 15th, Venus shines with
its own crescent lunar companion.
On Saturday, around 9:30 p.m. EDT with
an unobstructed view low to the western
horizon, try your luck detecting the crescent
Moon. Use this lunar guidepost to spot
elusive Mercury just below. The task will
benefit greatly from the aid of binoculars.
Sunday evening’s pairing of brilliant Venus
and a larger crescent Moon will be much less
challenging, requiring no optical aid other
than your keen eyes! Image courtesy of Sky & Telescope
Astronomy Club of Asheville
July 2018 Sky Events – the Planets
The Moon, Saturn and a Teapot
On the evening of Tuesday, July 24th,
the waxing gibbous Moon accompanies
the planet Saturn, separated by about 2
degrees and found in the constellation
Sagittarius, the Archer.
Situated in the south-southwest, above
Sagittarius’ well-known “teapot”
asterism, these two celestial objects
appear close in our 2-dimensional view.
Saturn is, however, positioned some 851
million miles behind the Moon.
While reflected sunlight from the Moon
reaches the Earth in just over one second,
Saturn is some 76 light-minutes distant!
Image courtesy of Sky & Telescope
Astronomy Club of Asheville
July 2018 Planet Highlights
Chart courtesy of
Sky & Telescope
Astronomy Club of Asheville
July 2018 Planet Highlights
Movement of the Sun, Moon and Planets this month
Chart courtesy of Sky & Telescope
Astronomy Club of Asheville
Moon Highlights – July 2018
**
** The “Thunder” Moon
Times shown are in Universal Time (UT) – subtract 4 hours to convert to EDT
Illustration and info courtesy of Sky & Telescope
Astronomy Club of Asheville
July 2018 Sky Events
July 6th - Earth Reaches Aphelion
Earth reaches aphelion – the farthest position from
the Sun in its annual elliptical orbit.
Distances in miles:
Aphelion ≈ 94.5 million
Perihelion ≈ 91.5 million
Average ≈ 93 million or Earth >
1 astronomical unit (AU)
~ the Earth-Sun distance < Sun
There is a 3.3% change in
the distance from aphelion Not to scale
to perihelion.Astronomy Club of Asheville
July 2018 Sky Events
July 6th - Earth Reaches Aphelion
On July 6th this year you may notice that you are
orbiting on planet Earth slower than usual! Here’s
why:
Kepler’s 2nd Law of
Planetary Motion Perihelion Aphelion
states that an
imaginary line joining
a planet and the Sun
sweeps out an equal
area of space in equal
amounts of time. Not to scale
As determined by Kepler’s 2nd Law of Planetary Motion, the speed of a planet along
its elliptical orbit is fastest when it is closest to the Sun (perihelion) and slowest when
it is farthest from the Sun (aphelion).Astronomy Club of Asheville
July 2018 Sky Events
All Eyes On MARS
The Red Planet’s Closest Approach for 32 Years
Avid skywatchers have had an appointment with July 2018 for years. Not since
2003 have the planet Mars and the Earth been positioned so closely together – an
occurrence not repeated until 2035 – making this summer’s Mars a “must-see-TV”
(telescopic-views) event!
Images courtesy of Sky & Telescope
Big changes in Mars’ apparent size as it approaches, and then recedes, from the Earth, providing detailed
views of surface features such as its southern white polar cap (shown at top in these images).
The planet makes its closest approach on the night/morning of July 30-31, when it
lies just 35.8 million miles away. Mars won’t be difficult to find; the rusty planet
peaks at magnitude –2.8, rivaling Jupiter at its brightest, and even outshines our
sky’s brightest star Sirius (magnitude –1.4) from June through September.Astronomy Club of Asheville
July 2018 Sky Events
All Eyes On MARS
The Red Planet’s Closest Approach for 32 Years
Why does this distance from
Earth vary so greatly? The Opposition Opposition
reason is the Red Planet’s March 2012 July 2018
highly elliptical orbit and how
the two planets align at their
closest points (called
opposition), about once
every 26 months.
When opposition occurs at or 100.78 million km 57.59 million km
near Mars’ perihelion (the (62.6 million mi) (35.8 million mi)
nearest point to the Sun in its
orbit), observers are blessed diagram not to scale
with a fine close apparition.
In contrast, oppositions which coincide with Mars at aphelion (its farthest point from
the Sun) provide shrunken telescopic views of the ruddy world, with few decipherable
planetary details. In 2018, Mars is at opposition with the Earth on July 27th; it reaches
perihelion on September 16th.Astronomy Club of Asheville
July 2018 Sky Events
All Eyes On MARS
The Red Planet’s Closest Approach for 32 Years
Locate Mars in the constellation Capricornus, rising in the
E-SE around 11:00 p.m. as July begins; Mars makes its
entrance just after 9:00 p.m. by month’s end.
Along with the excitement of a close peek at Mars, however,
there is bad news – the planet’s southern trajectory through
the ecliptic remains low in our skies, and sharp telescopic
views will likely be compromised by Earth’s thicker
atmosphere near the horizon. Just when you’re yearning for
perfect atmospheric seeing to discern fine details, unsteady,
True color image of Mars, taken turbulent air could spoil your enthusiasm!
by the Rosetta spacecraft in 2007
To improve your chances of capturing an unforgettable view, try when Mars is at its
highest and near the meridian – meaning well after midnight – and observe over multiple
nights for two (or more) weeks before and after the July 31st closest approach.
Mars was the Roman god of war. This summer a battle will wage to capture a glorious view
of the Red Planet before it recedes to more humble flanks in our skies – elude the engaging
action at your own peril…Astronomy Club of Asheville
July 2018 Sky Events
Delta Aquarid Meteor Shower
The Delta Aquarid Meteor Shower peaks in late July, with
estimates of 10-20 meteors per hour. These meteors tend to be
faint.
The peak night for 2018 is predicted to be Saturday, July 28th
and into the early morning hours of Sunday , July 29th.
The meteors, however, should be visible for a few weeks on either
side of the estimated peak dates, appearing to radiate from the
direction of the Delta star (called Skat) in the constellation
Aquarius – hence their name.
Look for these meteors between midnight and dawn, and an
unobstructed view of the sky at a dark location will increase your
observing success.
Unfortunately, in 2018 the shower’s peak night coincides with a
Moon just past its full phase, assuring that bright moonlight will
interfere with all but the brightest meteors!Astronomy Club of Asheville
July 2018 Sky Events
Delta Aquarid Meteor Shower
The view about
1:00 a.m. local time
on July 29th.
The Delta Aquarid meteors will appear to radiate from this area of the sky.End
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