Solar Eclipse Viewing

The solar eclipse starts at 6:20 pm and will attain maximum coverage around 50 percent at 7:20 pm.  We'll check that out from Open to the public viewing at Sommers-Bausch Observatory.  Then we'll head across the street to K's China rooftop deck to watch the sun sink behind the mountains while still partially covered just after 8:00pm.

6:30 -
Sommers-Bausch Observatory
Regent Drive
University of Colorado   map

8:00pm - K's China
1325 Broadway St   map
Boulder, CO 80302 

Maximum Eclipse View from the Moon A partial eclipse of the Sun will take place the afternoon of Monday, June 10th, 2002. This will be the last solar eclipse visible from Boulder for nearly a decade!

As seen from Boulder, 50% of the diameter of the Sun (39% of its area) will be obscured by the Moon at maximum eclipse, which occurs late in the afternoon, at 7:20 pm Mountain Daylight Time. Nowhere on the Earth will the eclipse be seen as total ... on the other hand, observers on ships off of the coast of Baja California in the Pacific will be treated to an annular eclipse, where the Moon appears to remove a round hole from the center of the Sun.

Sommers-Bausch Observatory and Fiske Planetarium, at the University of Colorado in Boulder, will be hosting a special Public Open House between 5 pm and 9 pm the afternoon and evening of June 10th to allow visitors to safely view the eclipse, and also to learn more about eclipses and to explore and the early evening skies. Weather permitting, visitors will be able to watch the Moon move across the face of the Sun during the hour-and-a-half eclipse, and will be able to pick out the outlines of lunar craters seen in profile against the glare of the Sun.

Because the eclipse begins late in the afternoon and occurs so low to the horizon, most of the the conventional astronomical instruments at the Observatory cannot be utilized this time around. Fortunately, our main solar instrument, the heliostat, will be just barely able to follow the eclipse until the Sun disappears behind the dome just after maximum eclipse (see below). Earlier visitors to the Observatory ... while the Sun is higher in the sky ... may have the opportunity (weather permitting, of course) to use the heliostat to view details of sunspots, solar prominences, and perhaps even a flare in real-time.


alt-az graphic

Although the other instruments of the Observatory won't be able to follow the eclipse, we do plan on having the 18-inch and 16-inch telescopes up and running to point out some bright objects, such as Venus and Jupiter, that can be viewed even in broad daylight!

In conjunction with the viewing at Sommers-Bausch Observatory, our next-door sister institution, the Fiske Planetarium, will also be showing visitors alternate ways to safely view the Sun and the solar eclipse using small telescopes: the full-aperture solar-filter telescope arrangement, and the image projection method. Also on hand will be pinhole projection cards, solar literature, as well as mylar eyeglasses (see below) for sale.

Following sunset at 8 pm, Fiske will be offering a free public show in the star theater about solar eclipses in general ... and meanwhile the Observatory will remain open until 9 pm to permit additional twilight viewing of the planets.


eclipw timetable




Some Q&A About Eclipse Observing

Safety First!

How does one view a partial eclipse of the sun safely? Any suggestions for contraptions people can make at home?

Let me first mention what NOT to do!

First, don't try to use your "naked" eyes to stare at the Sun .... although you'll find that your natural reflexes will probably prevent you from doing so anyway. People often ask, "Why is it more dangerous for people to look at the Sun during eclipses?". The simple truth is, "It's not ... staring at the bright disk of the Sun is ALWAYS potentially damaging to your eyes ... But ordinarily, you simply aren't motivated to look directly at the Sun, so you don't.

Second, DON'T try to view the eclipse with that new telescope or pair of binoculars! Partial blindness can instantly result as the intensified light enters your eyeball and sears your retina. And by all means, DO NOT even think about viewing the Sun with a telescope equipped with a solar filter that threads into the eyepiece - the glass can crack as it absorbs the intense solar heat, and instantly flood your eye with damaging light!

Now, there ARE ways to use these optical tools to indirectly view the Sun via the technique of "eyepiece projection" ... but unless you know EXACTLY what you're doing, and take great care to prevent someone from accidentally trying to "take a peek" to see where the light is coming from .... then it's best to leave this approach to the experts.

Third, don't rely on using dark photographic negatives, sunglasses, or conventional means to cut the solar glare; many of these materials may let invisible ultraviolet or infrared light through, so that even though you think it "feels" comfortable on your eyes, you may in fact be causing them damage.

So, what can you do? The safest and cheapest approach is to observe the Sun using "pinhole projection". Simply take two sheets of ordinary paper, and punch a pinhole in the middle of one. Go outside and hold the paper-with-pinhole flat towards the Sun. Then hold the second sheet in the shadow of the first. The sunlight will pass through the pinhole and form an image of the Sun on the second piece of paper! Ordinarily, this image is round, so most people just think it's an unfocussed blob ... in fact, you've almost certainly seen multiple versions of this kind of image on the ground already ... as sunlight filters through the leaves of a tree. However, as a "bite" is taken out of the Sun by the Moon during the partial eclipse, you'll easily be able to watch a chunk taken out of your projected image of the Sun as well. If the view is too dim in your pinhole projector, simply make the pinhole bigger. This will pass more light, although some detail becomes lost. If the Sun appears too small, simply move the two pieces of paper farther apart to magnify the image.


pinhole projector examples

To make things REALLY convenient, many people use paper plates instead of sheets of paper; and glue or nail them to each end of a wooden yardstick or other wooden frame so as to hold them with flat surfaces parallel to each other, but held rigidly apart. That way, you can hold the entire apparatus with one hand, and easily align the pinhole light from the upper plate onto the white surface of the lower one.

Others convert long carboard boxes into pinhole solar viewers: One side is cut away, so that the observer can peek in obliquely and see a white piece of paper (the viewing screen) glued to the inside of the lower end of the box. A pinhole is made in the opposite end of the box (because cardboard is thick, you'll probably want to cut a larger hole and cover it with a pin-pricked piece of tinfoil) ... and you're done!

Alternately, some forms of aluminized mylar sheets available at hobby shops reflect a sufficient amount of light at all wavelengths, visible and invisible, to be used as viewers. But beware, some of these let unseen light through, and some may have tiny pinholes from incomplete coating. To be safe, use only sheets that have been tested and approved for solar viewing material.

Better yet, you can pick up a pair of cardboard eyeglasses made from tested and safe mylar material from your local planetarium or hobby shop. For example, Fiske Planetarium, here at the University of Colorado here in Boulder, will be selling these safe, approved "glasses" for one dollar apiece while supplies last.


mylar viewing glasses


Other Eclipses

When was the last partial solar eclipse visible in Colorado? What about total solar eclipse? When will the next one be visible here in Colorado?

The last partial solar eclipse in Colorado occurred last year on December 14th, 2001... but the maximum coverage was only about 10%, and the whole event barely peeked out from behind the clouds.

The last one with good clear skies here in Boulder happened on May 10th, 1994. People living several hundred miles further south or east of Colorado got to see this one as an "annular eclipse" ... where the Moon passed fully in front of the Sun, but doesn't appear large enough in the sky to completely cover it up.

The next partial solar eclipse won't happen again for Boulderites for almost another ten years, the afternoon of May 20th, 2012. This one, however, will be a dramatic one, with over 80% of the solar disk being covered by the Moon.

As far as total solar eclipses are concerned, it depends upon whether you were, or are, willing to travel. The path of totality is so narrow, that any one fixed spot such as Boulder typically experiences a total eclipse only every 300 years or so. So, for instance, if you refuse to leave Boulder, then you'll experience a few "close calls", including an annular eclipse in 2348 ... but you'll have to wait until June 17th, 2672, to have complete totality come to you!

On the other hand, if you're willing to drive about 50 miles north of Cheyenne, you'll get to experience a total eclipse of the Sun on August 21st, 2017. And there was a total eclipse that passed over Castle Rock back on June 8th, 1918.


Partial versus Total Solar Eclipses

What causes a partial solar eclipse and why is the Sun only partially blocked out? How is this different from total eclipse?

It's simple experience that whenever something passes between you and a source of light ... any source of light ... that object blocks your view of it; alternately, you could say that the object's shadow fell across your eyes. It occurs everytime you hold up your hand to shade your eyes from the Sun.

And that's exactly what is happening during a solar eclipse ... except tht the intervening object is the Moon, not your hand.

The Moon can ONLY block the Sun at the time of a "new Moon" if it passes between us here on the Earth, and the Sun. We should probably call the new Moon a "no-Moon" instead, since at this time it's completely invisible to earthlings: first, because its illuminated face points towards the Sun and away from Earth; and second, because the darkside of the Moon - the side facing us - is up in the sky only in broad daylight and is completely lost in the glare of the Sun. We only infer its presence during those times when it passes almost exactly in a straight line between us and the Sun and blocks our view of it.

Then why don't we have an eclipse every month, at the time of every New Moon?

true shadow scale The way they draw eclipse diagrams in magazines and schoolbooks, that would certainly appear that that's the way things should happen. It's been made to appear that it is virtually impossible for the Moon not to pass directly in front of the Earth .... but in fact, it's quite easy for the lunar shadow to miss the Earth altogether.

The problem is, the Moon orbits the Earth MUCH farther away than can be sketched in any diagram that fits nicely in a textbook. In order to visualize the distance, we have to scale things down to a managable size. If the Earth is one foot in diameter (the size of a standard desk globe), then the Moon is the size of a softball, and orbits the Earth 30 feet away! It's the shadow cast by the softball that must fall somewhere across the surface of the globe, 10 yards distant, before an eclipse occurs. If the Sun-Moon-Earth alignment deviates by more than about one degree from a straight line, the shadow misses the Earth and no eclipse - not even a partial one - happens.

And since the Moon routinely can pass as much as 5 degrees above or below the Sun at new moon, then obviously we don't get even partial eclipses very often.

The conditions for a total solar eclipse ... where 100% of the bright disk of the Sun is blocked by the Moon .... are much more stringent. By a strange and fortuitous quirk of nature, the apparent size of the Moon and the apparent size of the Sun are virtually exactly the same to an earthling - both appear as disks in the sky almost exactly one-half degree across. In reality, the Sun is 330 times bigger than the Moon, but it is also about 330 times more distant. Hence, to get a total solar eclipse, you must completely cover up a certain-sized disk with another nearly-identically sized disk ... which requires that they must be lined up virtually perfectly. On the average, the alignment must be exact to within one one-hundredth of a degree! This precision arangement can only achieved, at best, at certain locations on the Earth, usually along a path only a few tens of miles wide .... so that's why you must be willing to travel if you hope to see a total eclipse in your lifetime!

And even if the alignment is perfect, that's still no guarantee that you'll experience a total eclipse - if the moon is near apogee (its greatest distance from the Earth in its elliptical orbit around us), then its disk will appear too small to completely cover the disk of the Sun - and we'll have an annular eclipse instead.

It is amazing - and some would say, perhaps by grand design - we live in only a brief period of the Earth's history during which spectacular total solar eclipses are created by the Moon. In several more million years, the Moon - which is spiralling away from the Earth at a rate of about one inch each year - won't be able to completely cover the Sun anymore, and total eclipses will be things of the past. And several million years in the past, the Moon was so close that when a total eclipse DID occur, it covered up the solar chromosphere that gives the Sun much of its interesting eclipse appearance.


See ya there! 

Jim's cell - 303.819.0053