2019-08-01_Sky_and_Telescope

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FROM OUR READERS

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Sinusoidal Tendencies

You may have gotten this question

many times previously, but please

explain again: Referring to the plan-

etary almanac (S&T: May 2019, p. 44,

for example), why does the path of the

ecliptic appear to be sinusoidal? Does

the projection or development of the

path of the ecliptic from the surface of

the celestial sphere onto the plane of

the paper result in this geometry?

William Woods

Weyers Cave, Virginia

Roger Sinnott replies: Both the

celestial equator and the ecliptic are

great circles. But, as you note, distortion

occurs in the rectangular projection when

a spherical surface is fl attened out onto a

sheet of paper. If the equator is made to be

a straight line, the ecliptic becomes roughly

sinusoidal. It would also be possible to plot

the ecliptic as a straight line, but then the

equator would become sinusoidal.

There is another type of projection,

the gnomonic, in which all great circles

are straight lines. But in this case there

As a mutual 65th birthday present, my childhood astronomy

buddy Al Bellg arranged for the two of us to tour and view

at the 40-inch refractor at Yerkes Observatory in Williams

Bay, Wisconsin. It turned out to be the very last clear night

for public observation before the observatory ceased public

operations. We brought our own 40-mm and 50-mm eye-

pieces to view Saturn and the Saturn Nebula, and we used

the focuser ourselves.

While driving home, we remarked on how simple that

giant scope was to operate: It uses setting circles, and the

process of fi nding objects is totally manual. We were tickled

to watch our host, a graduate student in astronomy at the

University of Chicago, grasp the wooden handlebars and

swing around the monstrous but fi nely counterbalanced

tube to center objects for viewing, using a 6-inch fi nder.

Wouldn’t amateur astronomy clubs line up for a series

of “rental” nights to use the scope? Could management of

Yerkes Observatory be shared by a consortium of amateur

groups, perhaps with a local college physics department

(there are two within 35 miles) keeping the keys and insti-

tuting a training program for representatives of the partici-

pating clubs? We’d love to see it happen!

Steve Marshall • Milwaukee, Wisconsin

is extreme distortion in scale across the

chart, and less than one hemisphere can be

shown on a gnomonic map. It is, however,

preferred by those who observe and plot

meteor showers. Each meteor’s track is

simply a straight line.

All’s Well with Caldwells

As we approach the 25th anniversary

of the Caldwell catalogue, I’d like to

take a moment to thank a small but

vocal group of curmudgeons for their

whirlwind of negative publicity that has

only helped vault the Caldwell objects

into mainstream use. The Astronomical

League’s Caldwell Observing Program

is thriving. Astronomy apps and Go To

databases identify Caldwells by default.

The public requests target views by “C”

number at outreach events. Even the

redoubtable Wikipedia highlights Sir

Patrick’s gems. Quite an impressive run

for a list of post-Messier suggestions

that started as a single Sky & Telescope

article (Dec. 1995, p. 38).

Stephen Saber

Rock Island, Illinois

Research and You Will Find

The letter titled “Problems at Home”

(S&T: May 2019, p. 6) expressed concern

that money is wasted on space explora-

tion and, in particular, SETI research,

which the writer believes “have little

value or relevance to Earth and its

inhabitants.... ” I strongly disagree.

During fi scal year 2018, the U.S.

federal government spent around $4.

trillion. Less than half of one percent of

that went to NASA and essentially zero

to the SETI Institute, an organization

funded mainly by private contributions.

Space research has already yielded vast

tangible benefi ts. Can you imagine

going back to a world without GPS, tele-

communications, or weather satellites?

Finding even bacterial extraterrestrial

life would be an astounding scientifi c

breakthrough; fi nding intelligent extra-

terrestrial life would be the greatest

discovery in the history of humanity.

That letter reminded me to make a

donation to the SETI Institute.

Bruce Flamm

Riverside, California

More Optical Mishaps

Bill Dellinges’s letter (S&T: June 2019,

p. 9) reminded me of a time when I

imaged the crystal-clear sky all night

with Amherst College’s 18-inch Clark

refractor. As dawn approached and I

enthusiastically gathered up my plates

for development, I couldn’t fi nd the lens

cap anywhere. Eventually I located it

perched safely atop the telescope’s tube.

After throwing away the undevel-

oped plates, I headed home.

Harold Heaton

Damascus, Maryland

In winter, my favorite fi rst look after

collimating my 12.5-inch truss Dob is

the Double Cluster, where I view the

small semicircle of stars a friend has

coined the “Cowboy Asterism” (the

semicircle is his head, and the bright

star beneath it is the medallion in his

string tie). One night I had the hard-

est time picking out the asterism. I fi rst

thought perhaps transparency was worse

than it appeared, then I began to wonder

if something was wrong with my eyes.

Last Look from Yerkes?

pAl Bellg got a look

through the 40-inch

refractor at Yerkes Ob-

servatory on Septem-

ber 26, 2018, the last

clear night for public

observation.

6 AUGUST 2019 • SKY & TELESCOPE