Follow the path of the two stars that make up the far edge of the Big Dipper's pan up to the first bright star. How does the sky move? For an observer on the earth, objects move from east to west this is true for both northern and southern hemispheres. More accurately put, when looking north, objects in the sky move counter-clockwise. Though all objects rotate in the sky , the observed path stars make in the sky depend on the observer's latitude. Do stars move? The stars move along with fantastic speeds, but they are so far away that it takes a long time for their motion to be visible to us.
You can understand this by moving your finger in front of your eyes. Even when you move it very slowly, it may appear to move faster than a speeding jet that is many miles away. In which country sun rises first? Why is the sky blue during the daytime? A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light.
When we look towards the sun at sunset, we see red and orange colours because the blue light has been scattered out and away from the line of sight. Can Sun rise from west? Planet Earth will move in the opposite direction some day and the sun will rise from the west!! Does the sun move? Answer: Yes, the Sun - in fact, our whole solar system - orbits around the center of the Milky Way Galaxy.
But even at that high rate, it still takes us about million years to make one complete orbit around the Milky Way! What is the position of the moon today? The Moon today is in a Waning Crescent phase.
In this phase the Moon's illumination is growing smaller each day until the New Moon. During this phase the Moon is getting closer to the Sun as viewed from Earth and the night side of the Moon is facing the Earth with only a small edge of the Moon being illuminated.
Where is Sun set? Finding The Stars and Constellations. Measuring the Altitude of the Moon. Why Astro? The Importance of Altitude and Azimuth in Celestial navigation. Bearing, Azimuth and Azimuth Angle. Learning from the Polynesians Survival — Star Compass 1. Survival — The Daytime Star. Survival — Calculating altitude without an angle measuring instrument. The Survival Sundial. Exercise 4 — Local Hour Angle. Celestial Navigation. Sight Reduction Forms.
Rising and Setting Times of Stars. Posted on June 9, by Jack Case. Links: Finding stars and constellations How to Locate Polaris. Like this: Like Loading This entry was posted in astro navigation , astronomy , celestial navigation , navigation , Uncategorized and tagged astro navigation , astronomy , celestial , navigation , Planning star and planet observations , Sidereal Time , star and planet observations. Bookmark the permalink. Leave a Reply Cancel reply Enter your comment here Please log in using one of these methods to post your comment:.
The spinning carries each star around in its observed circular path, while a special point in the northern sky, at the center of the circles, remains fixed. The sphere's rigidity accounts for how the shapes of the constellations never change, and its enormous size accounts for how the constellations never grow or shrink, as they would if a particular point on earth were significantly closer to one side of the sphere than the other. To better describe locations in the sky, we give names to the various parts of the celestial sphere.
The fixed point in the northern sky is called the north celestial pole , and is located only about a degree away from the famous North Star which makes tiny circles around it. Ninety degrees from the pole is the celestial equator , a great circle that runs from directly east to directly west, passing high above our southern horizon.
Mintaka , the rightmost star in Orion's Belt, happens to lie almost exactly on the celestial equator, so you can think of the celestial equator as tracing the path of this star. Another important great circle is the meridian , which runs from directly north to directly south, passing straight overhead.
As the sphere turns, the meridian remains fixed in the sky. The point straight overhead is called zenith. What about other locations? Moving east or west makes no difference, except to determine when you see things.
If you live farther east, you'll see any given star rise and set sooner; if you live farther west, each star rises and sets later. We compensate for these differences, in an approximate way, by setting our clocks according to different time zones. Moving north or south is more interesting.
The farther north you go, the higher in the sky you'll see the north celestial pole and the stars around it—and the lower all the stars will appear in the south. In fact, the angle between your northern horizon and the north celestial pole is precisely equal to your latitude. At the earth's north pole, you would see the north celestial pole straight overhead, and the celestial equator would lie along your horizon, so you would never see any stars rise or set; they would just move in counter-clockwise circles if you're facing upward, or horizontally to the right if you're facing the horizon.
Stars below your horizon that is, south of the celestial equator would always be hidden from your view. The Big Dipper will no longer always be visible, setting in the northwest and rising in the northeast instead. But in the southern sky, you'll see stars that are never visible in Utah, including the famous Southern Cross. Farther south, at earth's equator , the north celestial pole lies on the northern horizon, and the celestial equator passes straight overhead.
From here , as the constellations rise in the east, they appear to head straight up, rather than along a diagonal. In the west, they head straight down as they set.
Even more stars are visible in the southern sky, making clockwise half-circles about a point on the southern horizon, the south celestial pole. From the southern hemisphere, you can't see the north celestial pole at all. The south celestial pole, however, will appear above your southern horizon, by an angle equal to your southern latitude. Stars rising in the east will head upward and to the left , toward the northern sky. The celestial equator will also pass through the northern sky, lower and lower as you head farther south.
This several-hour-long time exposure, taken from tropical northern Australia, shows the clockwise motion of the southern stars around the south celestial pole.
The trails of the Southern Cross start at the top of the image, with the top of the cross initially above the edge. The ancient Greeks conceived the universe as a giant sphere of stars, surrounding the much smaller spherical earth. In this modern plastic model, however, the size of the earth is greatly exaggerated in comparison to the celestial sphere.
Finally, if you visit earth's south pole, you'll see the south celestial pole straight overhead , with the stars making clockwise circles around it. The celestial equator will lie on your horizon, with the stars moving parallel to it, from right to left.
You always see the same half of the celestial sphere, completely distinct from the half that you would see from earth's north pole. The explanation for all these effects is simply that the earth's surface is curved.
So when you travel to a different location, your horizon tilts with respect to the stars. Today every school child is taught that the earth is approximately a sphere. Even in ancient times, however, astute travelers realized that the changes in the stars as you travel north or south must be caused by the curvature of the earth. The ancient Greeks even reasoned that the earth must be a sphere, and thus pictured the universe as a pair of spheres: an enormous celestial sphere, carrying the stars around us once a day, and the much smaller spherical earth, fixed at the center of the universe.
The photo at right shows Orion near the western horizon. The photo was not taken from Utah. Once you understand how the earth's curvature makes the stars shift as you travel, you can easily determine the earth's circumference.
All you have to do is travel directly north or south for some measured distance, and measure the angular shift of stars near the meridian. Since the North Star is always very close to the meridian and easy to learn to recognize , it's probably the most convenient reference star. The only real difficulty with this measurement is that you have to travel pretty far before the shift becomes noticeable. If you're careful, though, you can measure an angular shift of one degree whenever you travel directly north or south by about 70 miles.
Now imagine continuing your journey southward. As you cross the equator, the North Star would disappear below your horizon, but you could continue to measure the shifts in the new stars that you see in the south.
Eventually you would come to the south pole, then continue past it, now traveling northward, back to the equator, then to the north pole, and finally around to your starting point. The stars have now shifted by a full degree circle, back to their original positions. And to accomplish this, you would have to travel a total distance of approximately. The earth's circumference is therefore about 25, miles. The circumference around the equator is also about 25, miles, though this is a little harder to measure.
You may find it easy to remember that at the equator, each of the 24 idealized time zones is about miles wide. Question: Did you check my calculation of the earth's circumference? If not, check it now! Which statement best describes my accuracy? Exercise: Use this value of the circumference to calculate the diameter of the earth in miles, rounded to the nearest thousand.
The first person known to have done this calculation was the ancient Greek astronomer Eratosthenes. Instead of using the North Star for reference he used the noon sun, which is also on the meridian.
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