Cumberland Times-News

Bob Doyle - Astronomy

June 9, 2012

Use sun, moon, stars to find your direction

Most of the time, you don’t need to know the compass directions — north, east, south or west. But knowing them can be useful.

For instance, if you are going to park your car for a few hours, you don’t want the interior of your car to be like an oven or sauna when you open up the doors. (I’m assuming that you would roll up the windows and lock the car doors to keep the contents secure.)

By knowing that the sun always moves to the right during the day, might allow you to park the car so the sun doesn’t shine onto the dashboard or steering wheels while you are gone, making both quite hot. I have found sunshades to be helpful as well.

At the start of the day, the sun seems to rise in the eastern part of the sky and ascends towards the south during the morning. (Really, the Earth is spinning or rotating, making the sun appear to roll across the sky.)

In midday, when shadows are shortest, the sun is due south and shadows point North. After midday, the sun continues to move rightward, slowly descending and then drops out of sight in the western part of the sky.

One approximate way of getting directions would be to face the direction where you last saw the sun, then your right shoulder will point roughly to the north while your left shoulder will point roughly to the South.

What if you miss sunset? If the crescent moon is in the western or southwestern sky, imagine the bow of the moon to be shooting an arrow towards where the sun earlier set, the direction west.

Or you can make a line from the moon’s upper tip through the lower tip and extend it downward; this line will point to the southern horizon.

What if you arise before the sun rises? If the crescent moon is also visible, imagine it to be a bow whose arrow will be aimed at the sun and to the eastern horizon where the sun will soon be rising.

You can also make a line from the upper tip of the moon through its lower tip, and extend it downward to the southern horizon.

In late March or in late September, the sun rises fairly close to East and sets fairly close to west.

Another way to get your directions at any time of the day is to stick a pencil into the ground. Mark the tip of the pencil’s shadow by a small rock. Then wait at least one half hour.

You will see that the tip of the shadow has moved. Mark the new shadow tip with another small rock. A line from the first small rock to the second small rock will point east, the opposite direction that the sun seems to move (towards the West).

What about at night? If you are in the Northern Hemisphere (north of the equator), the Big Dipper may be seen. It is a seven-star asterism (not an official constellation) that really looks like a Dipper with a bent handle.

The three handle stars are very well matched while the star joining the scoop with handle is a bit dimmer. The remaining three stars of the scoop are about as bright as the three handle stars. The end stars of the scoop can be extended about five times (towards the open side of the bowl) to find the North Star.

This star, named Polaris, is about as bright as the stars of the Big Dipper. The North Star is less than one degree from the North Celestial Pole (the extension of the Earth’s North Pole into space) so finding it will give you the direction north even more accurately than a compass (which points to Magnetic North).

The height of the North Star is approximately your latitude. (Our Tri-State area is about latitude 40 degrees north.)

If you are in the Southern hemisphere south of the equator), the North Star will be below the horizon.

You then must rely on the Southern Cross, a compact group that could fit into the scoop of the Big Dipper.

Extend a line from the top star of the Cross through its bottom star and extend this distance about four and half times; you will then be at the South Pole of the sky, where there is an absence of bright stars.

A line dropped straight down to the horizon from the celestial South Pole will give you an accurate fix on the direction South.

Can you get your directions from the moon in the middle of the night? If you see a moon with its lighted half downward (like a bowl) slowly descending, you are seeing the first quarter (half full) moon setting in the west.

If you see a moon with its lighted half downward but slowly getting higher, you are seeing the last quarter (half full) moon rising in the east. In the middle of the night, a nearly full moon will be in the south and its shadows will point north.

A few of these tips have come from “The Natural Navigator” by Tristan Cooley. This guide instructs how you can use trees, sand dunes, mosses, algae, even puddles and other natural features to get your directions.

This paperback was published in 2012 by the Experiment, LLC, has ISBN 978-1-61519-046-1 and is also available as an e-book.

THIS WEEK’S SKIES: The moon has fled into the morning sky, so the evening stars and planets shine without the interference of moonlight. Nearly overhead in the evening sky is the bright golden star Arcturus.

If you extend the Big Dipper’s handle outward, you can “arc” to Arcturus. Further along this arc is the bright planet Saturn and Virgo’s white-blue star Spica. (Saturn shines steadily while Spica noticeably twinkles.)

To the right of Saturn is the yellowish planet Mars. further to the right of Mars is the white-blue star Regulus of Leo. High in the east is another very bright star named Vega.

Two other bright stars below Vega form the Summer Triangle. Low in the southeast is the bright pink star Antares, marking the head of the Scorpion.

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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