Under the brilliant summer sun, is there such a thing as a safe, healthful suntan? Let’s take a look, starting with the sun’s mechanics.

Our nearest star, eight light-minutes away, is 330,000 times earth’s mass. Its immense self-gravity tries to crush it down to a hyper-dense neutron star, but the hydrogen from which it’s primarily made resists that compression with the gigantic outward-pushing thermal pressure of a four-and-a half-billion-year-old thermonuclear fusion reaction. Our solar ball is sized precisely at the balance-point between gravity and the heat of fusion.

In fusion, four protons crush together to become helium. If you were to use a very, very tiny scale to weigh an output helium particle against the four input protons, you’d find the helium weighs slightly less than the original particles. That delta-mass (.m) weight loss, multiplied by the speed of light squared, becomes pure energy: E = mc2.

Thus does our star shine.

It takes 100,000 years for the energy released in the core to reach the sun’s surface and radiate earth. This radiation is a mixed blessing. On the one hand, earth’s life depends on the sun. If its rays were to fail, the only life remaining after a few weeks would be some bacteria in thermal springs and ocean floor volcanic vents.

On the other hand, the sun is a blazing nuclear reactor that emits copious quantities of radiation that can break molecular bonds in things like, oh, cellular DNA. Our earth’s magnetic field and atmosphere filter out lethal solar particles and X-rays. But DNA-damaging ultraviolet (UV) radiation gets through.

(By the way, Martian astronauts will need shielding from ionizing solar radiation, as Mars’ absent magnetic field and thin atmosphere filter out nothing. Caves, anyone?)

The higher you go in altitude, the worse your UV exposure. In Nederland, we see a third more UV than at sea level.

UV damages skin. Full stop. No arguing. People with darker skin are less susceptible than lighter-skinned compatriots, but everybody experiences some damage. All people are adversely affected by UV radiation.

A suntan is the skin’s radiation-damage response. It might seem cool, but a tan says, “I’ve been hanging out in an ionizing radiation bath from a nuclear shot.” Which is not cool. Plus, tanning ages your skin prematurely, potentially giving you a gnarly look later in life.

And a sunburn? Well, that says, “I just got nuked by a radiation bomb.” It was not good at Bikini Atoll and it’s not good now.

Suntans and sunburns yield mutated DNA that can turn cancerous, even decades after exposure. Cancer is uncontrolled cellular growth; skin cancer can easily spread into the rest of the body. The result can range from difficult treatments to an unwanted meeting with The Grim Reaper.

Bottom line: There’s no “good” suntan.

Fry now, pay later.

When you’re in the sun, slather SPF-30 (or higher) sun-blocker. Remember your ears—I knew a paleontologist whose cancer started inside an ear where he’d habitually skipped sunblock. Wear a brimmed hat, collared shirt with long sleeves, and long trousers. Plus, get an annual dermatological exam.

Sunscreen safety note: UV blockers do not cause cancer; people who promote that ridiculous urban myth should be ashamed of themselves. As for Vitamin D, it’s in fortified food and over-the-counter capsules, if you think you’re short on it.

Now, get some happening sunglasses and have a great rest of your summer.

In July Skies:

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: New July 5; First Quarter July 15; Full (Buck or Thunder) Moon July 21; Last Quarter July 27.

July Meteor Showers: The Piscis Austrinids (parent unknown), Southern delta-Aquariids (parent, Jupiterfamily 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 to dawn. The Aquariids peak around 4 a.m., and the Capricornids are best around 2 a.m.

Best Sky Viewing Nights (Minimal Moon): July 1-14.

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 reaches its highest altitude above the horizon in the evening sky on July 12. Look for it from the western end of Barker Reservoir.

Venus is very low in the western evening sky, barely visible after sunset.

Mars rises around 2 a.m., and is low in the east at dawn. For a challenge, train a pair of binoculars on July 15 and spot Uranus above and to the left, about a full moon’s width away.

Jupiter rises just before 3 a.m. and is low in the east at sunrise.

Saturn rises around 11 p.m.; it is high in the south at dawn.

Notable Space Missions: This month we remember Apollo astronaut Bill Anders, who passed away in June at age 90. He flew to the moon with Frank Borman and Jim Lovell in the historic, first-people-to-the moon Apollo 8 mission in December 1968. In lunar orbit, the crew saw the earth rising above the lunar horizon. Grabbing their color-film camera with seconds to spare as the earth rose higher and higher, Anders took some on-the-fly photos while he had the shot. One of those became Earthrise, arguably the most famous and impactful photograph ever taken. It showed the earth as a blue-and-white speck in the vastness of space, in stark contrast to the lifelessly grey lunar surface in the foreground. Earthrise started the environmental movement, with the first Earth Day in 1970.

We will miss you, Bill, and your heroic cohort. Thank you for going to the moon, so that we could finally see our fragile paradise for what it is, a blue and white gem in the universe’s dark vastness.

Frank Sanders, a spectrum scientist at the U.S. Department of Commerce in Boulder, takes science and astronomy-related inquiries at backyardastronomy1@gmail.com.