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# Looking Up: Travelers can witness the changing sky

Peter Becker
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How much of the sky can you see at any one time? This, of course, assumes you are looking up from a wide-open, flat field or out on an ocean liner with nothing but a flat horizon no matter which way you look.

The entire sky includes every direction you can look from any point on the Earth’s globe. The total sky is referred to by astronomers as the celestial sphere. Thousands of years ago, the assumption was that the stars were points of light on a great overhead dome, seen from inside. It does look that way.

One may think the amount of this inverted sphere that you could see from a flat field is one half. That’s only true if you are positioned at the very north or south pole, or from the equator.

From the poles, however, all you ever see is the same half of the celestial sphere. From the equator, as the year goes along, you can see the entire celestial sphere, but only one half at any one time.

The Earth’s equator is directly under its counterpart on the celestial sphere, the celestial equator. The north and south poles, which mark the axis of the turning Earth, points directly to the north celestial pole (NCP) and south celestial pole, respectively. (The North Star is very close to the NCP.)

If you have an opportunity to travel a few hundred miles north or south, you can easily notice how the sky changes. I’ve made a few trips to Florida, and have always been fascinated to see how far down in the sky the North Star appears, as compared to my view in Pennsylvania.

The measure of the North Star above the northern horizon in degrees gives you your approximate latitude. From home, my latitude is almost 41 degrees 30 minutes. From mid-Florida, where we have relatives, the latitude is just shy of 27 degrees. The entire sky shifts approximately 14.5 degrees every time I travel to Florida.

The whole celestial sphere is measured in degrees. All the way around the entire sky is 360 degrees, a complete circle. The NCP is at (+) 90 degrees; the celestial equator is at 0 degrees. Latitude has its counterpart on the celestial sphere; it is referred to as “declination.” Longitude on the sky is referred to as “right ascension.”

From where I live, I cannot see any stars below 48 degrees south of the celestial equator.

There is an entire portion of the starry heavens awaiting me, from (-) 48 degrees to the south celestial pole (SCP) which is at (-)180 degrees.

It’s an incredible experience if you are familiar with the constellations, to see how they shift. The farther south I travel, the more stars are visible in the far south, which never break the horizon from home.

From Florida around Christmas time, in early evening, I am fascinated at the fact that the Big Dipper partly dips below the northern horizon, which never happens in Pennsylvania. The marvelous constellation Orion is rising in the east, but from Florida what an odd angle it makes!

FYI: The celestial equator, by the way, passes right through Orion’s three-star “belt.” From the ice at the north pole, during the 24-hours of night, you would see the top of Orion slowly moving around the horizon as the Earth spins.

From Florida on an early winter evening, I am amazed to see in the far southern sky the beautiful, bright star Canopus, far below Orion’s stars and the bright star Sirius. Canopus is invisible from Pennsylvania. At certain times from Florida, I have glimpsed the bright star Alpha Centauri, the closest star system to the sun. Alpha Centauri is very low in the southern sky from mid-Florida; it is better to travel even farther south to see it.

A whole new sky unfolds the more you head south. Perhaps you have had a chance to see the stars from the Southern Hemisphere; I have not had that chance. You can trace the Southern Cross and many more constellations never seen far north. Constellations you are familiar with seeing are upside down when viewed from below the equator. The moon even flips on its head!

Traveling north and south, you witness that the Earth is indeed round like a ball, and you can better appreciate the vast wonder of the stars all the way around.

Full moon is on Jan. 10.

Keep looking up!

Peter Becker is managing editor at The News Eagle in Hawley, Pennsylvania. Notes are welcome at news@neagle.com. Please mention in what newspaper or website you read this column.