Southern Colorado Skies / October 23 – 29, 2016

Consider a planetarium program to help you plan your observations. There are many commercial products available, and an excellent program (STELLARIUM) is available free at


All right, the approximate diameter. But it’s surprising how close you can get!

The high-tech equipment for this calculation is a piece of cardboard, a white piece of paper, and a tape measure. Make a pinhole in the cardboard as shown here.


Go outside on a sunny day and place your white paper 36 inches from your pinhole cardboard. You should see a faint circle (an image of the Sun) on the white paper (I used graph paper). Measure the diameter of the Sun’s image.


Here’s a diagram that labels the pertinent dimensions in your setup.


Now for the math. The ratio of the distance to the Sun (D) to the diameter of the Sun (S, which is what we’re trying to calculate) is equal to the ratio of the distance to the white paper (d, or 36 inches) to the diameter of the Sun’s image (s, which I measured as 11/32 inch). Because this is only a rough estimate, I used the average distance to the Sun of 93 million miles in the following calculation for D.



The actual mean diameter of the Sun is 865,000 miles, so I came within about 3% of the correct answer. Not bad, considering the method!


Wednesday (October 26)

Look to the southwest just after dark and you will be treated to Saturn, Venus, and Antares (in that order, from top to bottom) forming a nearly vertical curve.

Thursday (October 27)

Saturn, bright Venus, and Antares straighten out into a nearly vertical line.

Friday (October 28)

Saturn, Venus, and Antares in the southwest now bend the other way.


Mercury (in Virgo)

Mercury is lost from sight in the Sun’s glare.

Venus (in Ophiuchus)

Low in the southwest in the evening twilight..

Mars (in Sagittarius)

Look in the south-southwest at nightfall.

Jupiter (in Virgo)

Very low in the east at dawn.

Saturn (in Ophiuchus)

Look in the southwest at dusk. Saturn is to the upper left of Venus early in the week, then above Venus.

NASA’s Cassini mission is finishing up its final year of exploration (click here for NASA press release).

Uranus (in Pisces)

High in the east by nightfall Uranus will be at opposition on October 15th.

Neptune (in Aquarius)

High in the southeast by nightfall.


Sunday (October 23): 6:42 p.m. / Magnitude -6.3 / S / elevation 45 degrees

Monday (October 24): 8:09 p.m. / Magnitude -7.4 / NNE / elevation 30 degrees

Tuesday (October 25): 8:03 p.m. / Magnitude -4.5 / NNE / elevation 32 degrees

Wednesday (October 26): 7:20 a.m. / Magnitude -5.7 / SE / elevation 25 degrees

Wednesday (October 26): 7:57 p.m. / Magnitude -2.6 / NNE / elevation 34 degrees


These are too numerous to list here! If you’re serious, load the ISS DETECTOR app on your smart phone or tablet.

Have fun!

Dave Furry, SCAS Director of Education

SCAS rework Logo 3 Color copy

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