TUNGSTEN VALLEY - This month, the sun’s eleven-year activity cycle culminates with a peak in sunspot activity as its magnetic poles flip themselves over. That’s right, the sun’s magnetic field is only quasi-stable; its north and south magnetic poles reverse themselves every decade. (Our own planet’s magnetic field does the same thing, but the flipping interval is more like 250,000 years.)

As the sun’s poles approach their somersault moment, two things happen. One is that the overall magnetic field becomes squishy and blurry. It develops all sorts of little zones and islands where the field goes one way, neighbored by other areas where the field is the opposite. The sun develops a whole family of little, local magnetic fields instead of having a single, big unified field.

The second thing is that the field lines become extremely twisted, like yarn skeins or a bunch of twisted rubber bands. Where those twisted groups pass through the sun’s surface, energy flow through the surface is blocked and the surface cools. Those cool spots look dark; we call them sunspots.

As the eleven-year cycle culminates, the number of sunspots peaks. This particular go-around (called Solar Cycle 25) has been moderately active. On any given day between now and the end of this year, you will likely see at least a half-dozen sunspots, looking like pimples on the sun’s face. (For safe viewing, go to https://skyandtelescope.org/observing/observing-the-sun/.)

If you get around to watching some sunspots, here are a few things worth knowing. They are more than just dots. Each one has a dark inner zone called the umbra surrounded by a medium-dark area called the penumbra.

They superficially resemble Pacific island atolls. They evolve in a time period of many hours to several days. When a very large spot or even an archipelago of spots grows up, it will persist for at least a few days.

Although the spots look rather tiny on the sun’s face, their diameters are roughly the same size as our earth. That’s right, you could drop our entire planet into a single sunspot. That’s the operational size scale of our nearest star.

A few historical notes on sunspots and our sun in general: When Galileo first documented sunspots four hundred years ago, their existence added to his argument that the Universe was not centered on a corruptible earth surrounded by a divinely perfect firmament.

The reasoning? If God’s celestial heaven was unchangeable, then the sun couldn’t very well be having unsightly pimples breaking out all over its face, randomly coming and going every few days.

In the 1800s, British physicist Lord Kelvin argued that the sun could only be a few million years old, based on the heat of gravitational contraction from the solar system’s formation. His computation contradicted geological and biological evolutionary evidence that earth must be more like hundreds of millions to billions of years old.

The contradiction was only resolved in the twentieth century when nuclear fusion was identified as the sun’s power source.

Currently, the sun’s physical processes are still the subject of intensive scientific research, although our current administration is trying to kill our scientific research and erase its results in every way that it can manage.

Back to the days of Lord Kelvin!

July Fun Astro-Fact: It takes about one million years for the energy generated in the sun’s super-dense core to make its way to the solar surface and be radiated into space.

In July Skies:

Solar Max ramp-up: The sun’s 11-year sunspot cycle peaks in July; it’s climbing now. The next few months are your best opportunity to see sunspots. 

The sun begins the month in Gemini, entering Cancer on July 20. At mid-month, days and nights are 14 and 10 hours long, respectively. On July 5, we are at our maximum (not minimum!) yearly distance from the sun, called aphelion.

The moon’s dates are: First Quarter July 2; Full (Buck or Thunder Moon) July 10; Last Quarter July 17; New July 24.

July meteor showers: The Piscis Austrinids (parent unknown), Southern delta-Aquariids (parent, Jupiter-family comet P/2008 Y12), and alpha-Capricornids (parent, Jupiter-family Comet 169P/NEAT) peak on July 29 and 30. The Piscis Austrinids are best seen between midnight and dawn. The Aquariids peak around 4 a.m., and the Capricornids are best around 2 a.m.

Best sky viewing nights (minimal moon): July 7-21.

Sunset (mid-month): Altair is rising in the east and Deneb is low in the northeast. Hercules with the beautiful M-13 globular cluster is nearly overhead. Libra (twin bright stars Zubeneschamali and Zubenelgenubi) is low in the south with brilliant Spica to the right.

The box of Corvus is low in the southwest. The Big Dipper is high in the northwest, and Arcturus is high in the south. Distinctive Scorpius with red Antares is rising in the southeast

Midnight (mid-month): Sagittarius, marking the center of the Milky Way, our home galaxy, glows in the south. Scan its varied wonders with tripod-mounted binoculars or a wide-angle telescope.

Sunrise (mid-month): Orion is rising while the bright Pleiades cluster glints high in the east. Our nearest neighbor galaxy, M-31 Andromeda, is perfect for binocular viewing directly overhead.

Mercury, in Cancer, is as high above the horizon as it can get in the western sky at sunset on July 4.

Venus, in Taurus, is the Morning Star, high in the east and next to Aldebaran at sunrise.

Mars, in Leo, is low in the west at sunset. 

Jupiter, in Gemini, is very low in the east at sunrise.

Saturn, in Pisces, is high in the southeast at sunrise. With binoculars, go straight up two moon diameters and then very slightly leftward for Neptune.

Notable space missions: NASA’s TRACERS mission launches this month. It is a pair of synchronized spacecraft that will study our planet’s magnetosphere, which shields us from cosmic radiation.

Frank Sanders, a spectrum scientist, takes astronomy-related inquiries at backyardastronomy1@gmail.com.