Finding North by stars for beginners

Finding North by stars for beginners.

by tonytran2015 (Melbourne, Australia).

Click here for a full, up to date ORIGINAL ARTICLE and to help fighting the stealing of readers’ traffic.

(Blog No.85).

#find North, #finding North, #by stars, #star disk, #star map, #Mercator, #beginner,

Finding North by stars for beginners.

Beginners only need to know few stars to practice finding North by stars.

1. Common viewing instructions for all beginners.

1. From the following three maps select and print the one suitable for your zone.

Sky map Northern 3/4 sphere

Figure: Sky map (Inversion type) of the Northern Celestial 3/4-sphere showing only 20 brightest stars and some constellations. 24hr of R.A. is on the top and R.A. increases in the clockwise direction.

Sky map Southern 3/4 sphere

Figure: Sky map (Inversion type) of the Southern Celestial 3/4-sphere showing only 20 brightest stars and some constellations. 24hr of R.A. is on the top and R.A. increases in the anti-clockwise direction.

star map mercatorx1p6

Figure: The Mercator map of the sky for inhabitants of Tropical Zone. North direction is on its top. 24hr of R.A. is near the center and R.A. increases towards the left (East) of the map. The map is to be read South side up in the Southern hemisphere.

2. Use a shadow stick or a compass to find out the (true) North direction at your location.

shadow stick to tell time and find North

Figure: A shadow stick for finding North and time is drawn here in blue colour. The shadow of its tip always move WEST TO EAST along a conical curve C (drawn in red). The axis of symmetry of the curve C is the terrestrial North-South direction. (Conical curve: Elliptical, parabolic or hyperbolic curve).

3. Find out the latitude of your location.

4. Find out the current date in the calendar year.

5. Use the following simplified instructions to identify the stars at mid-nights.

2. Viewing instructions for inhabitants of Polar and Temperate Zones.

1. Place one of your straightened arm horizontally, pointing to North if you are in Northern hemisphere and South if in Southern hemisphere.

2. Raise your straightened arm by an angle equal to your latitude. Your straightened arm now points to the Celestial pole at your location.

3. Hold the circular star map on the hand of that arm, with its axis pointing to the Celestial pole and the MARKING FOR CURRENT MONTH ON ITS RIM AT ITS BOTTOM.

4. You can now see the images of stars on the map pointing to the actual stars.

sky disk alignment

Figure: Aligning the center of the paper star disk to the Celestial pole in the sky to identify the stars at midnight.

5. Beginners only need to recognize the circumpolar stars for their own hemisphere.

Inhabitants of Northern hemisphere need only to identify Little Dipper, Big Dipper (11hr R.A., 60° declination) and Cassiopeia (1hr R.A., 60° declination).

Figure: Finding North by stars for beginners (Northern hemisphere).

Inhabitants of Southern hemisphere need only to identify Agena, Alpha Centauri (pointer stars) and Acherna in the anticlockwise direction (all at 60° South declination). Acherna is 60 degree from the pair (alpha Centauri, Agena) and is on the opposite side across the Southern Celestial Pole.

Figure: Finding North by stars for beginners (Southern hemisphere).

Extending the line alpha Centauri-Agena by 8 degrees gives the Southern Cross Constellation. Then turning clockwise by 50 degrees and extending by another 50 degrees gives the very bright Canopus star.

In the opposite direction, extending the line Agena-alpha Centauri by about 30 degrees gives the stinger tail of the large, distinctive Scorpius constellation.

6. The knowledge of other stars will follow naturally with time.

3. Viewing instructions for inhabitants of Tropical Zone.

1. Hold the Mercator star map above your head, with North direction pointing to true North.

2. The length of the map corresponds to 13 months. Select and view only 6 month centered on the CURRENT MONTH. The line for the current month is worked out from the markings along the vertical lines of this Mercator map.

3. You can now see the images of stars on the map pointing to the actual stars.

4. Beginners only need to recognize some bright stars near to the Celestial equator: Orion Rigel and Betelgeuse of the large, distinctive Orion constellation, Procyon, Leo Regulus, Spica, Bootes Arcturus, Altair, Antares of the large, distinctive Scorpius constellation. They are associated with various different months of the year.

Equatorial Stars2

Figures: Finding North by stars for beginners (Tropical zone). Click to enlarge figure.

5. The knowledge of other stars will follow naturally with time (see Slide Sky-Map for displaying tropical stars.).

Bright Stars 20 Plus 2

Figure 2: Table of 20 brightest +2 stars in order of appearance.

4. Common Identifying instructions.

Sun on Celestial Sphere

Figure: The Sun, the Moon and the stars are attached to a Celestial sphere which encloses the Earth like a giant rotating cage.

1. Beginners should observe the identified stars in subsequent night as well as at various different time.

2. The circumpolar stars will remain visible all year round for cold temperate zones. Beginners only need to know them well.

3. The tropical stars appear in sequences and tropical inhabitants have to associate tropical stars with their months in the year.

4. Tropical constellations are seen upright from Northern Hemisphere and upside down from Southern Hemisphere

References.

[1]. tonytran2015, Shadow-stick-navigation-and-graph-of-solar-paths, posted on August 19, 2016.

[2]. wiki, Astronomical_ceiling_of_Senemut_Tomb.

[3]. Suchow map, http://www.adlerplanetarium.org/exhibits/planetary-machines.

[4]. wiki, Chinese_star_maps

[5]. tonytran2015, Finding directions and time using the Sun and a divider, survivaltricks.wordpress.com , Finding directions and time using the Sun and a divider., posted on May 6, 2015.

[6]. tonytran2015, Finding North direction and time using the hidden Sun via the Moon, survivaltricks.wordpress.com, Finding North direction and time using the hidden Sun via the Moon . Posted on July 6, 2015.

[7]. tonytran2015, Finding North direction and time by stars, survivaltricks.wordpress.com, Finding North and time by stars. Posted on August 28, 2015

[8]. tonytran2015, Finding accurate directions using a watch, posted on May 19, 2015 .

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Sky map Northern 3/4 sphere

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Slide Sky-Disks with grid masks showing azimuths and altitudes.

Slide Sky-Disks with grid masks showing azimuths and altitudes

by tonytran2015 (Melbourne, Australia).

Click here for a full, up to date ORIGINAL ARTICLE and to help fighting the stealing of readers’ traffic.

(blog No.28)

#find North, #finding North, #direction, #time, #slide, #sky, #star, #map, #disc, #disk, #star disk, #slide sky map, #slide sky disk, #slide star disk, #navigation, #declination, #right ascension.
Feature Figure: Illustration of a rotatable Sky map with an overlaid grid mask showing azimuths and latitudes of stars for a user at 40 degree latitude.

(Note: There was a software error which initially set the publication date wrongly on October 19th, 2016. The true publication date is Nov 3rd, 2016.)

It is an advantage to know the arrangement of stars for the nights before engaging in nightly activities such as going to the country side or navigating your way by stars. It is difficult to have a good display of the night sky with current commercially available circular star maps as they are equidistant-azimuthal and have a lot of distortion for visualization whereas easy visualization requires that groups of stars should appears with the same shape as actually observed in the sky and the constant altitude curves should be nearly circular around the zenith point.

The device given in this posting gives the desired displays with low distortion for the night sky. I give it the name Slide Sky-Disk (which is similar to the name Circular Slide Rules of similar looking mathematical devices used before the age of calculators).

It is made of two maps of stars and of interchangeable viewing grids to give elevation and azimuth angles of stars to observers located near to 0 degree, 20 degrees, 40 degrees and 60 degrees in latitude.

It will be useful to people who want to learn the stars by themselves or need to refresh their nightly detailed knowledge of the sky before going out. It is low cost, light weight, small, flexible, durable and quite portable. If made from waterproof materials, it may also be used as a low cost standby star maps for pilots, travelers, hikers and seamen (My is made from CD discs, flexible CD cases and plastic films, they are all waterproof).

The device is made by following instructions in the next 4 steps. PLEASE READ THROUGH ALL STEPS BEFORE STARTING ANY CONSTRUCTION.

Step 1: Making the base maps for the Slide Sky-Disks.

Sky-disk for Celestial Northern 3/4-sphere

Sky-disk for Celestial Southern 3/4-sphere

Figures 1, 2: Two base maps.

The two maps of the North and South regions of the Celestial sphere made by Inversion Projection (Stereoscopic Projection) are used for the Northern and Southern hemispheres respectively.

The maps are to be printed on both sides of a thick sheet of A4 paper to make a base disc. Alternatively they can be printed on ordinary A4 papers and pasted on the opposite sides of a thick disk used as the base disc. I used 2 CD discs and print the maps as their labels.

Step 2: Making rotatable overlaying masks giving azimuth and elevation on the Slide-Sky-Disks.

altitude azimuth grid mask for 00 degrees of latitude

altitude azimuth grid mask for 20 degrees of latitude

altitude azimuth grid mask for 40 degrees of latitude

altitude azimuth grid mask for 60 degrees of latitude

Figures 1, 2, 3, 4: The grid masks for observers at 0 degree, 20 degrees, 40 degrees and 60 degrees in latitude.

A grid mask is placed on top of the base map to read the azimuth and the elevation of the stars drawn on the map. The grid masks must match the type of coordinates used for drawing the Celestial sphere. An observer must use the mask drawn for his latitude.

Description of curves on grid masks:

The smallest circle of each grid is graduated into 12 intervals of 30 degrees each to show the azimuth angle of the star or direction from True North (or True South for Southern latitudes). The curves radiating from the center represent the great circles from the zenith to the terrestrial points of 0 degree (North), 30, 60, 90 degree (East) , 120, 150, 180 degree (South), 210, 240, 270 degree (West), 300, 330 (The North line points toward the map’s center in Northern hemisphere and away from it in Southern hemisphere.). The red circular arcs represent the constant elevation circles in the sky. They are placed at 30, 60 and 90 degrees from the zenith. The circle at 90 degrees from the zenith represents the horizon on flat locations. The graduation can also be read from the horizon circle toward the center to show the elevation angle of the star. The position of any star in the sky can be read against the grid.

Four grid masks are given here for use with both Celestial spheres. You have to select one that is based on a latitude nearest to your current latitude.

For latitude between 0 degree and 10 degree select the mask based on 0 degree latitude.

For latitude between 10 degree North and 30 degree select the mask based on 20 degree latitude.

For latitude between 30 degree North and 50 degree select the mask based on 40 degree latitude.

For latitude between 50 degree North and 70 degree select the mask based on 60 degree latitude.
You can make all four masks as each can be easily fit into and removed from the device as you move to a location with a different latitude.

Make each mask with the CORRECT size and print it at the CENTER of an uncut A4 waterproof transparent film by a photocopier. If this cannot be done you may have to print the mask on an ordinary piece of paper, place a transparent film on top of it and trace the grid lines onto the waterproof transparent film using a pen with waterproof ink.

Step 3: Making the grid holder for a Slide-Sky-Disk.

Figure: The grids holder is made from a flexible CD case.

The grid holder is made from a flexible plastic CD box. The front circular window has been cut for viewing the map. A small rear window is cut for moving the map. A grid is drawn onto a square transparent film and fitted to the front cover. It is to be held in place by the four plastic lugs (visible in the picture). The base map will be fitted on to the holding stub on the back cover and it can be rotated relative to the case and the grid on the front cover.

Step 4: Final assemblage of a Slide-Sky-Disk.
slide-sky-disk

Figure 1: Photograph of an actual Slide Sky-Disk fitted with a mask for 40 degree.

slide sky disc rotated

Figure 2: Photograph with Sky-Disk rotated anti-clockwise by about 25 degrees.
Push the CD with the picture of the chosen hemisphere onto the holding stub of the CD case. Make sure that it can be easily rotated inside the holder. Close the case and the Slide Sky-Disk is ready for use. The disc is rotated by access through the small window on the back cover.

Step 5: Using the Slide-Sky-Disks.

The sky at night is represented by the circular sky map centered on the corresponding Celestial pole under the transparent window carrying the grid showing azimuth and altitude (that is the disc rotates under the viewing window).

1/- Check that the center cross of the grid is on the declination line corresponding to your required latitude.

2/- Rotate the map to place the current date on the opposite side of the window. The map and the grid gives the view of the mid-night sky for the date.

3/- Then rotate the core map by half a division (15 degree on the equator or half a month) to decrease or increase the Right Ascension for every hour ahead of or after midnight. R.A. increases in the clockwise direction for Northern and counter-clockwise for Southern hemisphere.

4/- As the latitude for the grid is not being exactly that of the observer and the true time at the location is not being equal to the zonal time the slide star disk may not give very accurate values of elevation and azimuth angle for the stars within 30 degree of the zenith. However the lines joining these stars still give accurate directions and they help identifying other stars near the horizon. The stars near the horizon can be read from the Slide Sky-Disk with more accurate values of azimuth and elevation angles.

Examples:

The sky of December 21st can be visualized for any latitude using these Slide Sky-Disks in combination with a Slide Sky Map [3] .The view is CORRECTLY ORIENTED WHEN its December marking ON EACH DISK IS AT THE BOTTOM. You may have to click on each image to have a clearer view.

Sky map for Dec 21st at latitude of 60°N

 Sky map for Dec 21st at latitude of 40°N

Figures 1,2: Night sky on Dec 21st at latitudes of 60°N, 40°N, up side down view. The view is CORRECTLY ORIENTED WHEN its December marking ON EACH DISK IS AT THE BOTTOM.

 Sky map for Dec 21st at latitude of 20°N

 Sky map for Dec 21st at latitude of 20°N

Figures 3,4: Night sky on Dec 21st at latitudes of 20°N, upside down view. The view is CORRECTLY ORIENTED WHEN its December marking is AT THE BOTTOM ON THE DISK.

 Sky map for Dec 21st at latitude of 0°

 Sky map for Dec 21st at latitude of 0°

 Sky map for Dec 21st at latitude of 0°

Figures 5,6,7: Night sky on Dec 21st at latitude of 0°N. The view of Figure 5 is CORRECTLY ORIENTED WHEN its December marking is AT THE BOTTOM ON THE DISK.

 Sky map for Dec 21st at latitude of 20°S

 Sky map for Dec 21st at latitude of 20°S

Figures 8,9: Night sky on Dec 21st at latitudes of 20°S.

 Sky map for Dec 21st at latitude of 40°S

 Sky map for Dec 21st at latitude of 60°S

Figures 10,11: Night sky on Dec 21st at latitudes of 40°S and 60°S.



References.

[1]. tonytran2015, Finding North and time by stars. Posted on August 28, 2015

[2]. tonytran2015, . Posted on May 25, 2016

[3]. tonytran2015, Slide Sky-Map for displaying tropical stars, posted on October 7, 2016

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, posted on Circumpolar Stars Nth
, posted July 22, 2016

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Navigating with an AM MW radio receiver, posted January 17, 2017, The Scorpius constellation, posted January 8, 2017, The Orion constellation., posted December 26, 2016, Rice as emergency food., Using GPS in off-grid situations, Slide Sky-Disks with grid masks showing azimuths and altitudes, Slide Sky-Map for displaying tropical stars.

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Slide Sky-Map for displaying tropical stars.

Slide Sky-Map for displaying tropical stars

by tonytran2015 (Melbourne, Australia).

Click here for a full, up to date ORIGINAL ARTICLE and to help fighting the stealing of readers’ traffic.

#find North, #finding North, #direction, #time, #by stars, #Mercator, #sky map, #star map, #slide sky map, #navigation, #tropic, #declination, #right ascension.

slide sky map

Figure 1: Illustration of the Slide Sky-Map using the mask for 15 degree North latitude.
Slide Sky-Map for displaying tropical stars (blog No. 26).

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It is an advantage to know the arrangement of stars for the nights before engaging in nightly activities such as going to the country side or navigating your way by stars. It is difficult to have a good display of the tropical night sky with current commercially available circular star maps as they have a lot of distortion for tropical visualization whereas easy visualization requires that groups of stars should appears with the same shape as actually observed in the sky and the constant altitude curve should be nearly circular around the zenith point.

The device given in this posting gives the desired displays with low distortion for the tropical night sky and has been designed for use with latitudes between the two tropical lines. I give it the name Slide Sky-Map (which is similar to the name Slide Rules of similar looking mathematical devices before the age of calculators).

It is made of Mercator map of stars and of the viewing grids to give elevation and azimuth angles of stars to observers located near to 0 degree, 15 degree North and 15 degree South in latitude.

It will be useful to tropical people who want to learn the stars by themselves or need to refresh their nightly knowledge of the sky before going out. It is inexpensive, light weight, small, flexible, durable and quite portable. If made from waterproof materials, it may also be used as a low cost standby star map for travelers, hikers and seamen traveling in the tropic (my is made from waterproof sheets).

The device is made by following instructions in the next 4 steps. PLEASE READ THROUGH ALL STEPS BEFORE STARTING ANY CONSTRUCTION.

1. Making the maps for the core.

mercatorx1p6

Figures 1a: The Mercator map for the front of the core of the Slide Sky-Map.
star map mercatorx1p6

Figures 1b: An alternative Mercator map with star names for the front of the core of the Slide Sky-Map

mercator8fx1.6polarc30.jpg

Figures 2: The map on the reverse side of the core.

The map on the front of the core of the slide sky-map is a Mercator map with continuation by its repeat copy. The map here wraps around the Celestial equator by 600 degrees, meaning that it has about 1.7 times the width of the minimal Mercator map. The extra length allows the slider covering 180 degree in the East-West direction to be centered on any given longitude.

The two inversion maps of the North and South polar regions of the Celestial sphere are overlaid at the two ends of the same Mercator map and the combined map is placed on the reverse side of the core. The two insets represent the two polar regions of the Celestial sphere not displayed on the Mercator map. They help visualizing the two polar zones of the Celestial sphere, they can be easily joined to the polar sides of the Mercator map using shared common constellations present in both types of maps as stitching guides.

The core maps are to be printed on both sides of a thick sheet of A4 waterproof paper. This thick sheet of paper forms the core fitting inside the sleeves of next few steps. Alternatively the core maps can be printed on waterproof A4 papers and glued onto the opposite sides of a piece of thick waterproof board used as the core.

 

2. Making azimuth and elevation masks for the slider

mercator grid 00deg mask

Figure 1: The grid mask for 0 degree latitude.

mercator grid15d N.jpg

Figure 2: The grid mask 15 degree North latitude.

mercator grid 15d S.jpg

Figure 3: The grid masks for 15 degree South latitude.

A grid mask is placed on top of the core map to read the azimuth and the elevation of the stars drawn on the map. An observer must use the mask drawn for his latitude.

Description:
The smallest circle of each grid is graduated into 12 intervals of 30 degrees each to show the azimuth angle of the star or direction from True North. The curves radiating from the center represent the great circles from the zenith to the terrestrial points of 0 degree (North), 30, 60, 90 degree (East) , 120, 150, 180 degree (South), 210, 240, 270 degree (West), 300, 330. The concentric nearly circular curves represent the constant elevation circles in the sky. They are placed at 30, 60 and 90 degrees from the zenith. The curve at 90 degrees from the zenith represents the horizon on flat locations. The graduation can also be read from the horizon circle toward the center to show the elevation angle of the star. The position of any star in the sky can be read against the grid.

There are 3 grid masks given for this design. Select one that is based on a latitude nearest to your current latitude.

For latitude between 8 degree North and 8 degree South select the mask based on 0 degree latitude.

For latitude between 7 degree North and 23 degree North select the mask based on 15 degree latitude North.

For latitude between 7 degree South and 23 degree South select the mask based on 15 degree latitude South.

You can make all three masks as each can be easily fit into and removed from the device as you move to a location with a different latitude.

Make each mask with the CORRECT size and print it at the CENTER of an uncut A4 transparent sheet. Print the selected grid on a waterproof transparent film by a photocopier. If this cannot be done you may have to print the mask on an ordinary piece of paper, place a transparent film on top of it and trace the grid lines onto the waterproof transparent film using a pen with waterproof ink.

3. Making the slider (improved design, 2017, August 31).

slideskymap00

Figure 1: Photograph of an actual Slide Sky-Map fitted with the mask for the equator.

BrightStars20Plus2

Figure 2: Table of bright stars for the back side of the double layered slider sleeve.

Figure : The Mercator map of the sky for inhabitants of Tropical Zone. North direction is on its top. 24hr of R.A. is near the right side and R.A. increases towards the left (East) of the map.

The slider consists of a double layer white sleeve fitted with a transparent rectangular strip carried between its front layers.

Wrap a waterproof, white, thick sheet around the rectangular core map to make a white sleeve of no less than 360 degree along the East West direction of the core map (that is wrapping no less than two third of the length of the core map). The core should fit snugly inside the white sleeve and should be able to slide smoothly along its East West direction inside the white sleeve.

Cut a rectangular window on the front center of this white sleeve to reveal 180 degree width of the core map. The back of this white sleeve should be glued or taped to make it a proper sleeve.

Wrap another layer of the same waterproof, white material around the inner sleeve just made to make a white outer sleeve that fits snugly on the inner sleeve. The sleeve has now two layers.

Make sure that there is SUFFICIENT GAP between the two sleeves so that the core map can also be inserted into and can also slide in the GAP between the two front layers of the double layered slider.

Make the two layers stick together on their back sides by tapes or glue. Then cut the window through the outer layer so that the core map can be observed through the front window as if the slider sleeve was made of only a single layer.

Figure: The sleeve has two layers.

You may like to add the table of bright stars (Fig. 3) to the (uncut) back side of the double layered white sleeve to facilitate calling star names.

Choose the transparent sheet with the printed mask for your latitude. Cut it into a rectangular shape with 2 long arms extending from the East and West sides of the transparent grid mask. The rectangular transparent sheet has its width slightly wider than the width of the core map.

Insert the rectangular transparent sheet BETWEEN the two FRONT LAYERS of the double layered slider sleeve. Align the printed window of the transparent sheet to the cut window of the double layered sleeve. The East-West arms of the mask should be trimmed so that they only protrude slightly out of the double layered sleeve just enough to make easy insertion and removal of the mask.

In this way, any of the transparent mask can be fitted into or removed from the double layered sleeve whenever the user requires a new mask for his new latitude.

4. Final assemblage.

slideskymap15s

Figure 1: Front view of a Slide Sky-Map fitted with the mask for 15 degree South latitude.

slideskymap2backc100.jpg

Figure 2: Back view of a Slide Sky-Map.
Slip the core map into the inside of the double layered sleeve. The core map is now behind the transparent grid mask.

5. Usage.

The sky at night is represented by the core map going toward its west under the transparent window (that is it goes from left to right under the viewing window).

1/- Check that the center cross of the grid is on the declination line corresponding to your required latitude.

2/- The four vertical lines for equinoxes and solstices are printed on the core map. Other date lines are interpolated from them.

Place the center of the sliding window on the current date to see the mid-night sky for the date.

3/- Then slide the core map by half a division (15 degree on the equator or half a month) to the east or to the west for every hour ahead of or after midnight.

4/- The latitude for the grid not being exactly that of the observer and the true time at the location is not being equal to the zonal time causes the stars inside the smallest circle around the zenith to have slightly inaccurate position relative to the grid. However the lines joining these stars still give accurate directions and the stars still help identifying other stars near the horizon. The stars near the horizon have their values of azimuth and elevation angles given more accurately by the Slide Sky Map.

6. Record of a previous design.

(For reference only, do not use this obsolete design).

The slider consists of a white inner sleeve and a transparent outer sleeve tightly fit together.

Wrap a waterproof, white, thick sheet around the core (printed with maps) to make a white sleeve of no less than 360 degree along its East West direction (that is wrapping no less than two third of the length of the core map). The core should fit snugly inside the white sleeve and should be able to slide smoothly along its East West direction inside the white sleeve.

Cut a rectangular window on the front center of this white sleeve to reveal 180 degree width of the core map. You may like to add the table of bright stars (Fig. 3) to the (uncut) back side of the white sleeve to facilitate calling star names.

Choose the transparent sheet with the printed mask for your latitude. Cut it into the shape of a cross with 4 long arms extending from 4 sides of the transparent grid rectangle window. Each arm has its width equal to the size of the corresponding side of the adjoining window. Its North and South arms will be joined together to make a second, transparent sleeve fitting tightly outside the white sleeve, its long East and West arms will be slipped into the inside of the white, inner sleeve to anchor it on the white, inner sleeve. The East-West arms should protrude slightly out of the inner sleeve to make easy insertion of the sliding core into the white sleeve.

Wrap the transparent sheet tightly outside the inner sleeve and tape its North and South arms together to form a transparent sleeve with its grid right on the cut window of the inner sleeve. The East and West arms of the transparent sheet are slipped into the inside of the inner sleeve to lie along the East West direction underneath the white layer to anchor the transparent sheet on the white, inner sleeve.

In this way, any of the transparent outer sleeve can be fit into or removed from the inner sleeve whenever the user requires a new mask for his new latitude.

Slip the core map into the inside of the cardboard sleeve. Make sure that it goes behind the two transparent arms inside the sleeve so that it can travel fully from East to West.

Reference.

[1]. tonytran2015, Finding North and time by stars in the tropics, survivaltricks.wordpress.com, https://survivaltricks.wordpress.com/2016/05/25/finding-north-and-time-by-stars-in-the-tropics/, posted on May 25, 2016

RELATED SURVIVAL blogs

Navigating with an AM MW radio receiver, posted January 17, 2017, The Scorpius constellation, posted January 8, 2017, The Orion constellation., posted December 26, 2016, Rice as emergency food., Using GPS in off-grid situations, Shadow Stick Navigation, posted on 19 Aug 2016

, posted on

Circumpolar Stars Nth

. Posted on May 25, 2016

star map Mercator

Slide Sky-Disks with grid masks showing azimuths and altitudes, posted on 03 Nov 2016 ,

, posted July 22, 2016DirectionTimeByStars

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Finding time to Sunrise with star maps

Finding time to Sunrise with star maps

by tonytran2015 (Melbourne, Australia).

Click here for a full, up to date ORIGINAL ARTICLE and to help fighting the stealing of readers’ traffic.

#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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