Author Archives: Roger W. Sinnott

Roger W. Sinnott

About Roger W. Sinnott

Roger Sinnott is a senior contributing editor at Sky & Telescope.

Porter Garden Telescope Changes Hands

At the Boston auction house of Skinner, Inc., one of the most coveted of telescope collectibles recently went on the block. Barely more than a dozen of these elegant bronze garden ornaments from the 1920s are known to exist today.

January’s Surprise Comet

A major comet, known as Comet McNaught or C/2006 P1, is right now making its way through the inner solar system. It’s already as bright as the brightest stars, but it is also sticking close to the glare of the Sun.

July conjunction

Sky Highlights of 2007

As in any year, the starry heavens unroll with the seasons, and our solar system provides ever-changing sights much closer to home. Here's a taste of special events to watch for in 2007.

4-inch Clark refractor

Boston’s Classy Telescope Auction

The Skinner auction in Boston featured a stunning array of “brass and glass.” Many of the astronomical items came from the collection of Don Yeier (Vernonscope & Co.), himself the organizer of 12 previous auctions of astronomical instruments since 1974.

Pi

How many digits are satisfactory in the measurement of pi?

In the 3rd century BC, Archimedes proved that the ratio of a circle’s circumference to its diameter is less than 3 1/7 but larger than 3 10/71. That’s about 3.141. Later mathematicians have computed what we now call p (pi) to greater and greater accuracy — but how many digits are “enough”? The answer is…

When will (or did) the galactic equator cross the ecliptic very close to the latter’s northern and southern extremes?

As a teenager, when examining an equinox-1950 star atlas, I noticed that the galactic equator crossed the ecliptic very close to the latter’s northern and southern extremes (that is, the solstices at right ascension 6h and 18h). On equinox-2000 charts they are even closer. I’d love to know when the exact coincidence will (or did)…

How large an asteroid could a person jump off?

How large an asteroid could a person jump off? This interesting question goes back to 1952 or even earlier. It turns out that the asteroid must be no bigger than 3.9 v(ρe / ρ) kilometers in diameter, where ρ is the asteroid’s density and ρe is that of Earth in the same units (S&T: July…

Crescent Moon and Venus at sunset

Could the lunar crescent be seen in a telescope at new Moon?

Is the Moon’s orbit inclined sufficiently that, when it misses the Sun by the greatest amount north (or south), the lunar crescent could be seen in a telescope at new Moon? Probably not. The inclination of the Moon’s orbit to the ecliptic varies from 5.0° to 5.3°. French astronomer André Danjon (1890–1967) showed that no…

Rising Moon

How is the time of new (or full) Moon defined?

How is the time of new (or full) Moon defined? Astronomically, the Moon is new when it and the Sun have the same celestial longitude. The Moon is at first-quarter phase when its longitude is 90° greater than that of the Sun. The Moon is full when its longitude is 180° greater, and at last…

Dione

Do Saturn’s moons cast observable shadows on Saturn?

I’ve seen the tiny black shadows cast by Jupiter’s moons. Do Saturn’s moons cast observable shadows on that planet? Shadow transits of Titan, Saturn’s largest moon, have been seen with a telescope as small as 2 7/8-inch (73-millimeter) aperture. In 1891, two English observers saw the shadow of Rhea on Saturn with 6 1/2-inch instruments.…