Cumberland Times-News

Bob Doyle - Astronomy

January 5, 2013

Book reveals some interesting sky facts

A while back, I purchased an unusual paperback book called “Night Sky” by Nicholas Nigro.

This book is part of a series of Knack Make It Easy books that cover many types of cooking, house and home topics, music, child and pet rearing and lastly weddings!

This book is intended for sky gazers both in the northern and southern hemispheres.

The topics covered start with those important for beginners, then those for the intermediate sky gazers and at the end, the best objects likely viewed by those using binoculars and small telescopes.

This arrangement makes reading more suited for learning as some topics are covered several times, reinforcing the key ideas but adding more refinements.

“Night Sky” has a nice balance between text, diagrams and real images.

Each topic covers typically two to four pages, assuring some insights but not overloading the reader with details. You don’t have the read this book from cover to cover; you can instead read just one chapter at a time or even just one topic from that chapter.

Aside from a few mistakes, typical for a first edition, “Night Sky” is a book I would recommend for most readers interested in learning what’s over our heads.

Following are some space ideas from “Night Sky,” not usually covered in most novice sky books.

Our atmosphere has four layers, starting with the troposphere that blankets the Earth and contains 80 percent of the atmosphere’s weight.

The coldest part of the atmosphere is the upper layers of the mesosphere (above the stratosphere where jets fly), This is also the region of the atmosphere where pebble sized meteoroids burn up, causing what most call shooting stars.

The hottest part of our atmosphere is the thermosphere, reaching up to 600 km (400 miles) altitude. This region has a extremely low density so the International Space Station is not fried by orbiting through this layer.

Sundials work differently in the northern and southern hemispheres.

When we face the dial to read the time in our hemisphere, we face south. The shadow of the upright rod moves to the left or clockwise.

But in the southern hemisphere, the sun is in the north. As we face the dial to read the time, the shadow of the rod moves to the right or counterclockwise.

The number of stars seen in the southern hemisphere is larger than the star number in the northern hemisphere.

This is due to the center of our galaxy lying in the star group Sagittarius, which appears much higher in the southern hemisphere.

If we consider the stars and constellations visible every night in the north (for our latitude of approximately 40 degrees), there are no bright stars continually in view and just five star groups always on display.

But if we consider the skies of New Zealand (40 degrees south latitude), there are six bright stars always in view and nearly twice as many star groups always on display in the South.

But directions are not as easy “down under” as they can’t see our North Star, nor is there any South Star.

A consolation for those below the equator is that their air is clearer, as only 10 percent of the world’s population lives below the equator. With fewer people, less pollution and better sky gazing.

Why does the moon have grey plains (seen as the man or lady in the moon) and why does Mars look orange when closest to Earth?

The answer to both questions is the higher iron concentration on both the surfaces of the moon and Mars. On the moon, the grey plains are made of basaltic rock (just like our ocean floors) in contrast to the low iron surface of the highlands (where most craters lie).

The surface of Mars is covered with iron oxide (rust), with oxygen (oxide) from the early Martian atmosphere that bonded with iron in the soil.

SKY SIGHTS AHEAD: The moon is now a waning crescent in the morning sky. This Thursday at 6:30 a.m., the crescent moon will appear near the brilliant planet Venus.

With the moon absent from the evening sky, the winter stars and groups are at their best in the South. Orion with his three star belt is easily viewed.

The belt if extended up and to the right will take us to Aldebaran (the Bull’s eye) and beyond to the very bright planet Jupiter.

Orion’s belt if extended down and to the left will take us to Sirius, the night’s brightest star.

From our latitude, Sirius is the closest night star visible to the eye at a distance of 8.6 light years. (Alpha Centauri, a star seen from the tropics but not from our area is about half as far away as Sirius).

Bob Doyle invites any readers comments and questions. E-mail him at rdoyle@frostburg.edu . He is available as a speaker on his column topics.

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Bob Doyle - Astronomy
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