What’s Out Tonight?

A general ASTRONOMY site to get you started exploring the night sky

Our Sun

NEVER observe the Sun with any optical device including cameras, binoculars or telescopes! Permanent eye damage will result with just a brief glimpse. Special filters that cover the optics of these devices must be used to safely observe the Sun.  

Facts about the Sun

• It is the center of our Solar System because of its size.
• It’s energy is the reason for life on Earth. 

Diameter: 865,278 miles. 
Mass: 332,946 Earth’s mass 
Density: 1.41 where water = 1 (Earth is 5.5) 
Gravity: 27.9 times that of Earth 

Rotation on Axis: 25 to 35 days 
Inclination of Axis to Earth’s Orbit: 7.2° 

Composition: 92.1% Hydrogen, 7.8% Helium plus traces of all other elements 

Temperatures: 10,000° F on surface. 
Sunpots are a cool 6,300° F. 
Core of Sun reaches 27,000,000° F 

Age: 4.6 billion years. Will last another 5 billion years or so. 

The Sun
How often do we stop and think of the Sun when we think of the day? I think we take our days and nights for granted because they are natural, automatic cycles, like breathing. And, more importantly, how often do we think of the Sun when we think of life on Earth? The energy from the Sun is the reason that life developed and is sustained on Earth. 

Although the Sun is special to us, it is like all the other stars in the sky. Stars are created in a simple and natural process. They are the most common celestial object in the Universe. And, galaxies represent their abodes, where these fiery balls are congregated, where they are born, live and die. 

Nuclear Fusion and the Sun’s Life 
Our Sun is a typical or average star. Like all stars, its energy comes from nuclear fusion. Four hydrogen atoms are fused (forced) together to create one helium atom in the core of the Sun. The mass of the resulting helium atom is 1% less than the total mass of the four hydrogen atoms. The 1% difference in mass produces the energy that we see as the blazing Sun. About five million tons of matter are converted into energy every second in the core of the Sun. Fusion in the Sun is triggered by the tremendous pressure at the core, brought about by the sheer mass of the Sun. The Sun does not collapse upon itself because of the outward expansive pressure of the generated energy. 

The Sun is about 4.6 billon years old and will last for another 5.5 billion years. Toward the end of its life, it will become a red giant with an outer atmosphere extending to about the orbit of Mercury. During its final days, the Sun will shed its outer layers in one final heave. Outwardly, this heave will produce a planetary nebula while the core shrinks inward to become a white dwarf, an object no bigger than the Earth but with significantly more mass and a high surface temperature. 

Structure of the Sun 

Nuclear fusion occurs in the interior core where the temperature reaches 27,000,000° F. Outside the core is a radiative zone where a process of energy absorption and re-emission takes place. This zone transfers energy from the core to the convection zone that lies below the visible surface. The convection zone has huge circulating currents that transfer the energy from the radiative zone to the surface. It takes about 200,000 years for light to make its way from the core to the surface. 

The visible surface, called the photosphere, is composed of a lattice of cells, each about the size of Texas, called granules. Granules are the tops of the convection currents that bring the energy from the convection zone to the surface. Sunspots are visible on the photosphere and are associated with strong magnetic fields that restrict the convection currents, creating cooler areas that appear darker against the brighter photosphere. Sunspots are about 6,300° F compared to an average surface temperature of 10,000° F. 

Immediately above the photosphere is a thin layer of gases about 2,000 miles thick called the chromosphere. The temperature there ranges from just 7,600° F near the photosphere to 14,800° F at its outer edge. 

Beyond the chromosphere is the corona, the most tenuous part of the Sun’s atmosphere. This rarified hydrogen gas reaches temperatures of up to 1,800,000° F and extends for millions of miles from the surface. The corona is visible during total solar eclipses as the irregular halo surrounding the Moon. 

Prominences (as pictured in the 4th middle picture from the top) are massive protrusions of ionized gas carried from the surface of the Sun into the corona. They usually protrude outward but sometimes loop back to the surface. Large prominences easily extend 10 to 30 Earth diameters from the photosphere. 

A flare is like a prominence but releases enormous amounts of energy and energetic particles into the Solar System, causing the aurorae on Earth as well as radio and communication disruptions. 

The Sun produces a solar wind made of highly ionized gas that permeates the Solar System. This gas can reach speeds up to 435 miles per second with a density varying from 160 to 1,600 particles per cubic inch. Additionally, sunlight itself exerts a small amount of pressure. Both the solar wind and radiating sunlight are responsible for pushing a comet’s tail away from the Sun.

An illustration of our Milky Way Galaxy showing the location of our Sun (the yellow circle). Our Sun is located in the Orion-Cygnus arm. Farther out from us is the Perseus arm and closer in is the Sagittarius arm.

Sunspots on the surface of the Sun that can be seen with amateur telescopes equipped with a white-light solar filter. This is an image from the site solarham.com which provides a great wealth of current images of the Sun.

Close-up of a sunspot with a white-light filter. Each of the small and many granules is about the size of the state of Texas. On a very “clear” day, it is possible to see detail close to what is shown in this picture. The white-light solar filter is the least expensive solar filter that can be purchased. 

Our Sun as imaged through a special Hydrogen-Alpha filter that allows ​prominences to be visible. Amateurs can purchase special filters or telescopes to see the Sun as pictured.


There is only one safe way to view the Sun with a telescope, and that is to use a solar filter that completely covers the front of the telescope (the actual filter may be the same diameter as your telescope or could be smaller). All other types of filters or methods are dangerous! 

Solar filters can be purchased at your local or internet telescope store and/or through retailers that advertise in the popular monthly astronomy magazines. 

DO NOT attempt to make your own filter. Solar filters transmit about 1/100,000 of the Sun’s light and filter out harmful rays. Once the filter is fastened securely to the front of the telescope, use the telescope in a normal fashion. 

IMPORTANT: Remember to cover up your finderscope or reflex-sight finder — better yet, remove it! These also present viewing hazards and/or can be damaged by the Sun if they are not covered. To point the telescope at the Sun, let the telescope’s shadow be your guide. Move the telescope until the shadow of its tube is smallest. The Sun should then be in or near your eyepiece field of view if you are using a low magnification around 50x. 

The Sun emits so much energy that many of its features are overpowered by its brilliance. With a regular, white-light solar filter, only the photosphere and sunspots are visible. A special hydrogen-alpha filter is required to view prominences. 

Sunspots are plainly visible with a regular, white-light solar filter. They form, grow and dissipate, rotating with the Sun, changing their appearance daily. The inner and darkest part of a sunspot is called the umbra, while the surrounding lighter area is called the penumbra. Sunspots often appear in groups composed of many larger and smaller spots. There is an 11-year waxing and waning cycle of sunspot activity, however, the length of this cycle can vary by a few years. 

In order to view prominences, telescopes must be fitted with a special hydrogen-alpha filter or you can buy a small telescope which incorporates a hydrogen-alpha filter. These start at around $700. 

Hydrogen-alpha filters transmit only a very narrow range of light on the red end of the spectrum where prominences are visible. Prominences cannot be seen with regular light-white solar filters because they get “washed out” among all the other colors that these filters transmit. Without a hydrogen-alpha filter, prominences can sometimes be seen around the edge of the Moon during a total solar eclipse.
The hydrogen-alpha filter provides incredible views of the Sun. Not only will you see prominences, but you will also see the Sun’s mottled surface as well as the chromosphere. Changes in prominences occur hourly. I highly recommend making inquires at your local planetarium, club or telescope store about the possibility of observing the Sun through a hydrogen-alpha filter.

A refractor telescope fitted with a white-light solar filter at its front. Notice that the finder has an orange plastic cover for personal and equipment safety. 

A small refractor telescope with a built-in hydrogen-alpha filter. This telescope, called the Personal Solar Telescope or PST is around $700 — this does not include a mount or tripod. It is shown on a home-made mount and tripod. The piece of cardboard at the front is to keep the Sun off of one’s head when observing.