The Nearest Star

Today, we’re kicking off a new series on observing the solar system.  And we’re starting at the center of it all with the sun, the closest star to the Earth.

Many stargazers don’t bother observing the sun, and that’s a shame.  Solar observing has the delightful advantages of doubling your available observing time and helping you indulge your interest in astronomy without staying up far past your bedtime.  And solar observing gives you the singular opportunity to see the drama and raw power of a real star in grand detail.  Even in a small telescope, when properly equipped, can show you fascinating and dynamic phenomena on a star that even the biggest telescope could never hope to reveal on any of the stars in the night sky.

Some particulars about the sun:

Diameter: 109x Earth
Volume: 1.3 million x Earth
Mass: 330,000x Earth
Density: 1500 g/cubic centimeter in the core, 0.0000002 g/cubic centimeter in the photosphere (the part that we see)
Surface gravity: 28x Earth
Composition: 73.46% hydrogen, 24.85% helium, 0.77% oxygen, 0.16% iron
Rotation period: 25.4 days (yes, the sun rotates, just like the Earth and all the other planets)
Luminosity: 3.846 x 10^26 watts
Spectral type: G2V (a yellow-white main sequence star)

Like all stars, the sun was formed out of clouds of gas and dust that condensed into a nebula much like the Orion Nebula.  Once the dust cleared, our star found itself nestled in the loose gravitational embrace of its sibling stars in a small open cluster.  After a hundred million years or so, the sun’s birth cluster was dispersed into the galaxy, and our sun carried on alone in its 250 million year revolution about the center of the Milky Way.  Astronomers would dearly love to identify the stars that formed along with the sun, but so far, they have not succeeded.

An image of the sun through a H-alpha filter, showing solar flares

Finally today, some words of warning.  In your budding enthusiasm for solar observing, here are some things you should NEVER do:

• Never look at the sun directly, even with your unaided eye, even through thick haze, for any length of time

• Never look at the sun through a telescope, even your finder scope.  Although you’ll feel no pain because your retina has no nerve endings, you will be permanently blinded almost instantly.

• Never leave a telescope unattended outside in the daylight, especially around children, unless caps or solar filters are securely place over the main objective and the finder objective.  At the sight of a telescope, the curious and uninformed just might try a little solar observing, either accidentally or deliberately.  You should treat a telescope in daylight like a loaded gun.

• Never use a solar filter designed to thread into the eyepiece.  These filters are often supplied with cheap telescopes.  All the light from the sun is focused through the telescope onto these sad little filters, which eventually crack or melt allowing concentrated sunlight to suddenly hit your eye.  This happened to me once, and I just pulled my eye away in time!

• Never use as a solar filter smoked glass, sunglasses, layers of photographic film, photographic filters, sheets of Mylar from a camping blanket, or the bottom of a beer bottle (yes, it’s been done, though it’s not wise); none of these will protect you sufficiently.

Astronomy presents few opportunities for grievous personal injury, but solar observing is one such opportunity.  Be CAREFUL.

In the next installment on solar observing, we’ll give you some insight into simple solar filters you can use with your unaided eye or with your telescope to help you get started as a solar observer.