Finding time to Sunrise with star maps

Finding time to Sunrise with star maps

by tonytran2015 (Melbourne, Australia).

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#determine, #find, #find North, #time, #Sunset, #Sunrise, #time to Sunrise, #time to Sunset, #sky disk, #star disk,
Finding time to Sunrise is needed for traveling across deserts as the travellers may want to be on time to avoid excessive heat and coldness. It is also needed by long distance traders and country people who have to schedule their peak activities around Sunrise time.
Finding time to Sunrise is harder than to Sunset because the Sun is not seen before Sunrise (for people in tropical and temprate zones)! This method relies on the symmetry between Sunset and Sunrise to work out the time to next Sunrise using a circular sky map.

1. Mark the direction to the setting Sun

sunrise1

Use two rocks or a stick lying on the ground to mark the direction of the setting Sun.

2. Start a stop-watch.
The interval from Sunset to alignment of star maps may be significant (See the note at the end of step 5.).

3. Aligning stars and the Sun to star map

sunrise2

sunrise3

sunrise

Figure 1: Aligning the sky map to the stars and Celestial axis OP. Figure 2: Constructing the half-plane containing the Celestial axis OP and the half-line pointing to Sunset position. Figure 3: The intersection between the sky map and the Sunset half-plane gives the radial line OC.

Accurately align one of the star maps (such as of this article) to the stars and align its axis to the Celestial axis so that it points to the upper Celestial pole P. Work out the half-plane of constant R.A. containing the Celestial axis and the Sunset direction half-line. This half-plane intersects the polar sky map along a radial line which is often non-horizontal. Use a paper clip to mark the intersection C of the rim of the star-map disk and the half-plane.

4. Stop the stop watch.

PolrNorthNC20const8

 

polrsouthp4

 

Figure 1: The sky map for use in Northern hemisphere. Figure 2: The sky map for use in Southern hemisphere.
Stop the stop watch and note the time from Sunset to time of alignment of the sky map. This time varies from 5 minutes in the tropic to nearly one hour in the cold temperate zones (See the note at the end of step 5.).

5. Adjustment of alignment of the Sun
Use the stop-watch reading to determine the small amount of time from Sunset to the successful alignment of the star map. The paper-clip on the rim should be moved to a new position toward the bottom of the sky map by an angle corresponding to the time interval given by the stop-watch.
The paper clip should now be on the R.A. half-plane containing the Celestial axis and the Sun. The Sun has moved further down under the horizon corresponding to the rotation of sky map since Sunset to alignment time.
The stop-watch of steps 2, 4 and 5 is not necessary if the rotation of the Celestial sphere during that time interval can be worked out by any other mean such as from the rotation of an early Moon which is visible both before and after Sunset.
6. Coarse time to Sunrise.
The rising Sun will be the left-right reflection image of the setting Sun through the true North-South plane . So are the two corresponding positions of the paper clip. The sky map will rotate during the night and the paper clip will move through the position for Sunrise. The time to Sunrise is the time for the sky map to rotate between its current position and Sunrise position. (One full circle is 24 hours).

7. Alternative coarse time to Sunrise by the late Moon.
A late Moon remains in the sky until Sunrise. The shape of the Moon indicates the direction of the out-of-view Sun. The Celestial axis can be determined from the declination of the Sun and the local latitude. So time for the Sun to reach the horizon can be estimated. This method has been given previously.
8. Fine time to Sunrise.

Sunrise5

Observe the identifiable stars near the 90 degree Eastern horizon. They always rise up at the same angles (along the constant declination lines) from the same terrestrial directions on the horizon. Before the stars fade at Sunrise, pay attention to those that have risen about 1 to 5 degree from their rising positions and take notes of their travel (at angle to the horizon, along the constant declination lines) from the initial rising positions on the horizon. The stars rise 1 additional degree early for each subsequent day and new stars will appear to take their role. Using these stars close to the Eastern horizon, the time to Sunrise on subsequent days are determined with better accuracy.
Notes.
1. The motion of a new or early Moon in the sky can be used to time the interval from Sunset to alignment of the star map (by checking its rotation with the sky map). A stop-watch is not required in such a case.
2. If a large sky map is drawn on a wheel mounted on its axis aligned along the Celestial axis then a time keeper only needs to align the sky map to the stars at night and the paper clip to the Sun during day time to read fairly accurate local time from the travel of the rim of the wheel. The paper clip will make one complete rotation everyday and its position on the sky map needs adjustment by only 1 degree each day.
References

[1]. tonytran2015, Finding North direction and time by stars, Additional Survival Tricks, http://www.survivaltricks.wordpress.com/, posted on Aug 28, 2015
[2]. tonytran2015, Finding North and time with unclear sky, Additional Survival Tricks, http://www.survivaltricks.wordpress.com/ , posted Oct 17, 2015.
[3]. tonytran2015, Finding time to Sunset with bare hands, Additional Survival Tricks, https://survivaltricks.wordpress.com/2015/11/11/finding-time-to-sunset-with-bare-hands/, posted Nov 11, 2015.

[4]. tonytran2015, Finding North direction and time using the hidden Sun via the Moon, Additional Survival Tricks, http://www.survivaltricks.wordpress.com/ , posted Jul 06, 2015.un/, posted May 24, 2017,

 

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Finding time to Sunset with bare hands

Finding time to Sunset with bare hands

by tonytran2015 (Melbourne, Australia).

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#bare hands, #determine, #find, #find North, #time, #Sunset, #Sunrise, #time to Sunrise, #time to Sunset.

Finding time to Sunset with bare hands (Blog No. 11).

There are times when you have no watch or when it is not practical to carry a watch (such as when going for a swim in the sea) and you need to know the time from Sunrise or to Sunset. This time can be determined reasonably accurately using only your bare hands.

1. Hand postures

image

Figure. Hand posture for determining time to Sunset in the Northern hemisphere.

Cup your hand as if about to hold water. Position the wrist to have the thumb on top with four fingers horizontal and close together. Then stretch your arm, keeping all fingers at right angle to the stretched arm. Stand with your chest facing the Sun but DO NOT LOOK INTO THE SUN. Interpose the bent fingers on your stretched arm between the Sun and your aiming eye on the same half of your body. Twist the stretched arm to have the bent fingers forming with the horizon an angle equal to the local latitude angle and the contact line between middle finger and ring finger being on the same plane with the Celestial axis (Tilting the fingers from the horizontal by an angle equal to latitude angle is close enough).
The Sun will travel at right angle to your fingers to its setting position on the horizon .
Count the finger widths from the Sun to its setting position. Each finger width is about 1.5 degrees distance and is equal to 1.5×4 = 6 minutes of time to setting on equinoxes or is equal to 6.6 minutes of time to setting on solstices.
(At solstices, the length of the trajectory of the Sun is only (6.24radius)x cos(23.5degrees), so each 1degree of length corresponds to 4.4minutes of time).
For example, four finger widths to setting point gives 4×1.5×4 minutes of time to setting at equinoxes or 4×1.5×4.4 minutes of time to setting at solstices.

2. Notes

1/- In the Northern hemisphere the Sun moves to the right (North) when setting.
2/- In the Southern hemisphere the Sun moves to the left (South) when setting.
3/- The Sun is between the middle and ring fingers if any small gap between them let through strong rays of light.
4/- Your finger width on your stretched arm may sustain an angle different from 1.5 degree. You need to check it against the diameter of 0.5 degree of the rising or setting Moon.
5/- In Northern hemisphere, the Sun rises to the right (South).
6/- In Southern hemisphere, the Sun rises to the left (North).

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Finding North direction and time using the Moon surface features

Finding North direction and time using the Moon surface features.

by tonytran2015 (Melbourne, Australia).

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#find North, #finding North, #compass, #direction, #time, #Moon, #surface features, #natural compass rose, #navigation, #survival

This article shows how to use the Moon for finding direction and time.
The surface features of the Moon can be used as a compass rose for Earth inhabitants.

1. An upside down natural compass rose

Near to full Moon the phase (waxing-waning) and horn-line methods are not accurate. Right at full moon they are not applicable. However at those times we may obtain directional information from the global map of the Moon using the colour and shade of its surface (soil) features. Since moonlight is only reflected light from the Sun and is not intense and we may look at the Moon’s surface for the features.

We have to identify the features of the Moon associated with Lunar own rotational poles, so that the Moon can be placed and aligned on an upside down compass rose aligned for the rotation of the Earth.

Each of us may have have different individual visualization (or a simplified picture) of the Moon to orientate its poles on such compass rose. My own visualization for the shades on the Moon is a small lion licking the face of a kneeling monkey and it is drawn on the Moon in the title figure.

image

Figure: The surface features of the Moon is used as the core of a compass rose.

2. An oscillating core of the compass rose !

image

Figure 1: Moon as an oscillating core of a compass rose.

image

Figure 2: Moon as an oscillating core of a compass rose.

image

Figure 3: Moon as an oscillating core of a compass rose.

Consider that compass rose an UNDERNEATH view of a normal compass rose and you can use it for finding directions when it is high in the sky. (The leading side of the Moon, with a lion visualization, is on our West and its trailing side, with a monkey visualization, East). However the North of the Moon is the North pole of Lunar rotation axis and it makes an angle with the axis of the Earth, the angle sometimes reaches 23.5 + 1.5 = 25 degrees. Imagine that you can walk on the Celestial equatorial plane and the Lunar axis is planted on it at an angle of 90-25 degrees and you go around it once every 27.3 days.

Looking at that inclined Lunar axis, you will see that axis alternately tilted to your right hand then to your left hand. Looking from the earth, the axis of the Moon appears to oscillate clockwise and anti-clockwise (with amplitude equal to the lunar orbit angle, which requires complex calculations, and can be up to up to 25 degrees ) as the Moon orbits around the Earth. This compass rose only gives correct orientation when the Moon is made oscillating inside it ! The North of the Moon is aligned to 0 degree only when the Moon goes through its maximum or minimum value of Lunar declination (at furthest distance to the Celestial equator). When the Moon crosses the Celestial equator, the angle between Moon axis and Celestial axis is highest in absolute value..

So we have a natural compass rose but we must remember that Moonscape features does not easily give accurate direction and the Moon oscillate inside our Earth aligned compass rose between up to +25 and -25 degrees as well as tilling its poles toward or away from us. The title figure of this article is made for the reference, mean orientation of the Moon, when its axis is at right angle to the line of view and its equator is aligned to 90-270 degree marks of the graduation ring. Users intending to use the compass rose on any full Moon should check the orientation of the surface features against the East West directions (given by Waxing-Waning rule and by adjusted horn line method) two or three nights prior to the full Moon. Otherwise an uncertainty of up to 25 degrees should be allowed with this compass rose.

3. Lunar navigation needs a combination of methods.

MoonShapesNAngles5C

Figure 1: Moon phase chart for a Solar declination of (-20) deg (South).

tiltedhornlinec2.jpg

Figure 2: Panoramic view of the travel of the Moon.

MoonRosePath
Figure 3: Panoramic view of the travel of the Moon.

Navigating by the Moon becomes easier when we do it nightly on consecutive nights and keep records from previous nights. At half-Moon times we can use the Waxing-Waning rule and my improved horn-line method (given in p2) to draw the Celestial axis line on the Moon then record the position of the horn-line on the featured surface. At full Moon times we use Lunar surface features with the angle for the Moon obtained previously from the 3/4 Moon nights.We have to remember that the horn-line rotates almost steadily about each full-Moon.

Alternatively, the if we form the habit (when we have to navigate) of daily recording the direct measurements of Lunar declination, from the Moon and the Celestial pole (by either stars at night or the Sun before Sunset), we have accurate values of Lunar declination. The Moon and its declination can then replace the Sun in my method of determining direction and time (reference [3]). The accuracy is further improved if we combine the knowledge of our latitude, the phase and elevation angle of the Moon to predict its trajectory for the night (therefore we already have had an initial estimation of the North-South direction).

After the North-South direction has been found it is easy to tell time from a full Moon as the Moon is trailing the Sun by about 12 hours.The estimation is more accurate if we apply extrapolation to our own records of Moon rises and Moon sets on previous nights. When there is no Moon, we have to use stars and that will open new topics.

With lots of switchings among methods, the navigators may find that finding direction and time via the hidden Sun as given in reference [1] the simplest.

References

[1]. tonytran2015, Finding North direction and time using the hidden Sun via the Moon,https://survivaltricks.wordpress.com/2015/07/06/finding-north-direction-and-time-using-the-hidden-sun-via-the-moon/, posted on July 6, 2015

[2]. tonytran2015, Finding North direction and time accurately from the horn line of the Moon. https://survivaltricks.wordpress.com/category/moon-horn-line/
posted on August 12, 2015

[3]. tonytran2015, Finding North direction and time using the Sun and a divider, http://www.survivaltricks.wordpress.com/, 06 May 2015.

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Using polarized light to locate the Sun when it is hidden from view.

Using polarized light to locate the Sun when it is hidden from view.

by tonytran2015 (Melbourne, Australia).

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#find, #finding, #Sun, #North, #navigation, #survival, #find the Sun, #polarize, #light, #ray, #Sunlight, #Sunray, #sunglasses, #compass, #direction, #time

Anti-glare polarizing sunglasses reduce horizontally polarized rays. They can also be useful in locating the Sun even when it is hidden from view by clouds or by the horizon. Locating the Sun enables determination of compass direction and time for navigation without any compass.

1. Basic information

Two walkie-talkies are in the best condition for communication when their two antennas are parallel and at right angle to their line of view. The electric waves traveling between them have their electric field parallel to the emitting antenna and the varying electric field is at right angle to the line of transmission. The electromagnetic waves is said to be polarized in the direction of the emitting antenna.

Light is just electromagnetic waves at much higher frequencies than our familiar radio waves. Light can be polarized too. Light rays from incandescent sources are randomly polarized like radio waves coming from a walkie-talkie which is randomly orientated before each transmission. On the average we don’t see any polarization from a source with randomly changing orientation. However after a partial reflection (accompanied by a partial transmission) at an interface between two transmission media, the reflected and the transmitted rays from any non-polarized ray becomes partially polarized.

Polarizing sunglasses can favour light polarized in one direction and discriminate against light polarized in the other direction. With the same pair of sunglasses we can see two different colours and brightnesses depending on the orientation of the glasses when viewing the same source. This is illustrated in the following figure.

Be certain that your polarizing glasses really reduces sunlight reflecting off horizontal road surfaces before trying subsequent instructions here; each of the glasses must be individually tested and its direction of polarization verified.

2. Different colours and degrees of brightness seen from the same source of light through polarizing sunglasses

skylight through polarizing sunglasses

The cross with two different colours on the source denotes the two different colours seen through two orientations of the same sunglasses.

3. Seeing the polarized lights of the sky

polarization of scattered blue sunlight

The polarization of scattered blue sunlight in the sky

Blue light from the sky is the result of Rayleigh scattering of photons from sunlight by molecules in the sky. This scattered light is highly polarized as seen in the following practice:

Search for a large clear patch of sky with no cloud. Look through the polarizing glasses. Rotate the glasses about the axis of view to see the sky lightens and darkens alternatingly with the angle of rotation. The darkening is most profound when the Sun is at right angle to the line of view.

4. Locating the hidden Sun.

Locating the hidden Sun using polarized light

Locating the hidden Sun from two patches of clear sky.

1/- Search for a large clear patch of sky with no cloud. Rotate the glasses about the axis of view until the clear sky becomes most darkened. The Sun is then on the great circle perpendicular to the line joining the left and right spectacles (Being the intersection of the Celestial sphere and the symmetry plane of the sunglasses). The darkening is most profound when the Sun is at right angle to the line of view.

2/- Repeat with a second clear patch of the sky. Two large clear patches of the sky can give out the position of the hidden Sun. It is at the intersection of the two so obtained great circles in the sky.

3/- The position of the Sun below the sky-line can also be found using polarized light-rays from the clear sky above its (underground) line of view. If the illustration picture of this section is turned up side down with a horizon line added above its Sun it will illustrate how to find the Sun when it is below the horizon (The polarization is most profound on the clear sky at 90 degree to the (underground) line of view of the Sun.).

Reference [2] gives some interesting history of the early applications of polarization of light. Currently there have even been hypotheses that the Vikings had used polarized light to locate the Sun since antiquity with pieces of birefringent calcite crystals [1].

References.

[1]. Cahal Milmo, Not just the stuff of legend: Famed Viking ‘sunstone’ did exist, believe scientists,
The Independent, http://www.independent.co.uk/news/science/archaeology/not-just-the-stuff-of-legend-famed-viking-sunstone-did-exist-believe-scientists-8521522.html, 06 March 2013, 21 May 2015.

[2]. Unknown Authors, Polarization (waves), Wikipedia, http://en.wikipedia.org/wiki/Polarization_%28wave… 26 May 2015

[3]. Unknown Authors, Following the Light of the Sky, polarization.net, https://www.polarization.com/compass/compass.html… Accessed 16 May 2015 05:40:14 GMT.

[4]. tonytran2015, Finding North direction and time using the Sun and a divider, http://www.survivaltricks.wordpress.com/, 06 May 2015.

(The following is added after 20 May 2017)

[5]. Israel Ramirez, https://www.quora.com/What-can-animals-that-can-see-the-polarization-of-light-see-that-other-animals-cannot, 28 Nov 2016.

[6]. tonytran2015, Finding North in the polar zones using equatorial stars and the Sun, https://survivaltricks.wordpress.com/2017/05/24/finding-north-in-the-polar-zones-using-equatorial-stars-and-the-sun/, posted May 24, 2017,

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