Meet The Sun, Our Home Star – Sky & Telescope


The Sun’s Vitals

Apparent magnitude -26.7
Distance from Earth 150 million km = 1 astronomical unit
Type Main sequence, G2
Color White
Mass 1,988,500 x 1024 kg = 1 M
Radius 695,700 km = 1 R
Constellation varies
Right ascension varies
Declination varies
Multiple system? No
Variable star? Yes, slightly variable over an 11-year cycle
Exoplanets status 8 planets
5 recognized dwarf planets
2 major debris disks
Probable fate White dwarf

Physical Characteristics

The Sun with trees in the foreground
The Sun
Daniel Johnson

In most cases, other stars appear as points of light. We can record their brightness over time or divide it by color and study the spectrographs to infer a great deal of information about their compositions and distances. But, with a few notable exceptions, we can’t visually observe stellar surfaces in any significant detail.

Not so with the Sun. Its proximity offers us an unequaled chance to study an individual star. But how typical is the Sun? It’s not the most common type: much smaller red dwarfs make up about 75% of all the stars in our galaxy. It’s also a singleton, whereas almost half of Sun-like stars, are part of a stellar group.

Regardless whether the Sun is typical, it’s certainly stable: As a main sequence G2 star in the prime of its life cycle, the Sun’s consistent luminosity is critical to life on Earth. While the Sun is technically a variable star, the energy output over the course of an 11-year solar cycle changes by only 0.1%. 

Compared to some other types of stars, the Sun is stable in other ways, too. It’s not whirling around so fast that it threatens to tear itself apart, the way Regulus is; it’s not a red or yellow giant rapidly consuming its fuel at a breathless pace, as are Betelgeuse or Antares. And while the Sun does exhibit the occasional flare or eruption, it does so in a fairly gentle manner, unlike irregular stars such as Proxima Centauri. Whether the Sun’s typical or not, it’s extraordinarily friendly to life.

Like Earth, the Sun contains a complex internal structure with multiple layers. The immense gravity in Sun’s core, the inner quarter of the star, heats it to an unbelievable 29 million ºF as hydrogen atoms squeeze together into single helium atoms. This sustained nuclear fusion releases tremendous levels of light and heat (not to mention neutrinos), which escape to the churning surface and beyond. The Sun, as a result, shines like a blacksmith’s iron glowing in a blazing forge.

Inside the solar onion
This cutaway of the Sun shows its core, where nuclear fusion occurs. Around the core are additional layers: the radiative zone, convection zone, and the three layers of the solar atmosphere: photosphere, chromosphere, and corona.
NASA

The Sun’s surface churns, though it may look smooth through solar scopes. Granules, the convection cells akin to boiling water in a pot, cover the Sun like an irregular honeycomb. Occasionally, dark sunspots intrude on the surface, created as regions with intense magnetic fields trap and cool gas.

With only a few exceptions, all life and activity on Earth is powered directly or indirectly by the Sun’s energy. Solar panels are becoming ever more popular, but plants are the original and ultimate solar collectors. The leaves of trillions of trees worldwide (not to mention other plants) transform solar photons into energy every day.

Sunrise through a tree
Sunrise shining through tree, plants and the sun work together to power all life on earth.
Daniel Johnson

The Sun’s influence extends far past Earth. Only the Voyager 1 and 2 spacecraft have traversed the heliopause, a region where the Sun’s influence gives way to that of interstellar space.

Origin / Mythology

The Sun’s impact on daily life is so enormous that every ancient culture wove the Sun into its traditions and myths. We’ll explore just a sampling of interesting examples:

  • Greek — The Olympian character most commonly associated with the Sun is the archer Apollo, while Helios personified the Sun itself. Helios still has a significant presence in modern science; the element helium, first discovered in the Sun, was named for him. There is also the heliocentric model of the solar system, and the region of the Sun’s solar wind influence called the heliosphere. The Roman culture, which inherited or assimilated many Greek concepts, replaced Helios with the Latin Sol, a name also still in widely use today.
  • Egyptian – For thousands of years, the Egyptian culture recognized Ra as a deity who piloted the Sun across the sky in a boat. However, Aten was the name for the actual solar disk. The Aten was famously promoted by the revolutionary pharaoh Akhenaten, father of Tutankhamun.
  • Hebrew – In the book of Joshua, the Sun famously stood still in the sky (perhaps an annular eclipse), allowing for an extended day that permitted the Israelites victory over their enemies.
  • Ancient Central and South America – Despite the challenging jungle conditions of their home in Central America, ancient Mayan astronomers kept careful records of sky events. They built their observatories, like the one still standing at Chichen-Itza in the Yucatán, to align with the Sun on solstices and equinoxes. The Sun featured in nearby Incan and Aztec cultures as well.
Chichen-Itza
The pyramid of Kukulcán in Chichén Itzá is aligned to showcase the solar equinoxes.
Daniel Schwen / CC BY-SA 4.0
  • Chinese – Evidence suggests ancient Chinese astronomers observed and recorded sunspots millennia ago.
  • Polynesian – In one Polynesian tale, the Sun once sped along in the sky too fast for anyone to accomplish work during the short day. Popular folk hero Maui catches the Sun with net of rope and holds it still until the Sun promises to move more slowly. 
  • Cherokee – A Cherokee myth begins with the Sun being jealous of her brother, the Moon, because the people of Earth always look up at the Sun with squinted, unpleasant expressions, but they look at the Moon with a gentle smile because he isn’t so bright.

How to See the Sun

Obviously, you don’t need directions to find the Sun the way you might search for a dim star on a star map. But on the other hand, the Sun can be tricky to observe precisely because it’s so bright — it can cause eye damage when viewed directly.

Basic and inexpensive eye protection such as eclipse glasses can reduce the amount of light reaching your eyes to a safe amount, and you can watch for sunspots in this manner. But they don’t offer magnification, and it’s easy to forget (because we don’t typically look right at it) that the Sun isn’t that big. It’s the same apparent size on the sky as the full Moon, so it’s challenging to make out much detail without optical aid.

For this reason, many fans of solar astronomy use solar filters on their telescopes to reduce the light intensity to a safe level and block harmful radiation like UV rays. Another technique involves projecting the magnified image of the Sun through the telescope onto a wall or piece of paper. Both options will permit you to view and record interesting phenomenon like sunspots, prominences, and other details.

Pinhole projection
The author using a simple cardboard tube and a tinfoil pinhole to project an image of the Sun.
Daniel Johnson

Another DIY option is to magnify the Sun using a simple pinhole projector. A long tube can produce a satisfyingly large image of the Sun on a piece of paper on the other end.

Pinhole projection image of eclipsed Sun
A one-inch image of the Sun, from a simple pinhole projection during the 2017 solar eclipse.
Daniel Johnson

The Sun is fun to explore at other wavelengths, too. Amateur radio astronomy offers another way to enjoy the Sun, and you can see ultraviolet images from NASA’s Solar Dynamics Observatory.

Finally, remember the Sun is a solar system object that generally follows the ecliptic, as the Moon and planets do. Tracking these movements and recoding the positions of the rising or setting Sun over the course of the seasons can help you better grasp our place in the cosmos.


Daniel Johnson is a Wisconsin-based freelance writer and professional photographer and the co-author of over a dozen books. He’s a longtime amateur astronomer and fortunate enough to live in a rural region with excellent seeing conditions. You can view some of Dan’s photography (he does a lot of animals!) at foxhillphoto.com.


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