Finding North from unclear sky around April.

Finding North from unclear sky around April.

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.124).

#find North, #finding North, #direction, #by stars, #Spica, #Bootes Arcturus, #Antares, #April, #unclear sky
Around April there are some bright stars shining the whole night. They include Spica, Bootes Arcturus and Antares. These three stars can be used to locate the Celestial poles in the sky and subsequently the terrestrial principal directions.

1. Celestial poles and terrestrial directions.

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.
To an Earth bound observer, the Earth appears to be enclosed by a large rotating spherical shell called the Celestial Sphere with all stars attached to it. This shell rotates around the Earth nearly one revolution every 24 hous. This rotation leaves unmoved only 2 points on the shell. They are called the Northern and Southern Celestial poles of the Celestial Sphere.

If an observer can locate one Celestial pole then the projection to the ground of the line from him to the pole will be along his terrestrial North South direction.

2. Locating the Northern Celestial Pole in Northern hemisphere.

Figure 1: Stars in the Northern hemisphere rotates anticlockwise around the North pole.

An observer in Northern latitude above 30 degrees will see the rotation of three bright stars Vega, Deneb, Capella then Big Dipper constellations in that order.

Big Dipper constellation goes highest around 22 hr.

3. Locating the Southern Celestial pole in Southern hemisphere.

Figure 1: Stars in the sothern hemisphere rotates anticlockwise around the North pole.

An observer in Southern hemisphere or on the tropical zone would see the Southern Cross Pointers for the whole night.

4. Locating the Celestial poles from tropical stars.

Figure 1: 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.

An Earth bound observer in Southern hemisphere or on the tropical zone can identify the forward swept broom (or a duck foot (?), a bird foot (?) or a tree with 3 upper branches (?)). formed by the brightest star Sirius and four surrounding bright stars Canopus, Orion-Rigel, Betelgeuse and Procyon. The line Canopus to Sirius make the 35 degrees long broomstick handle and three lines from Sirius to each of the other three stars form three branches of the forward swept broom head (see the star maps). Sirius to Procyon is the trailing branch of the (three branched) broom head.
Doubling the travel from Sirius to Procyon takes us to another bright star named Pollux.

Two thirds of the line from Procyon to Pollux is a point on the Ecliptic (the great circle containing the.Sun and all planets). Turning anticlockwise 100 degrees at this point and traveling by a distance of 40 degrees takes us to a less bright star Leo Regulus. Keeping the direction from that two thirds point to Leo Regulus and travel for another 50 degrees takes us to a brighter star Spica. Spica is 90 degree in distance from the that two thirds point. (Observers from the Southern Hemisphere may also see that the great circle arc going through the long axis of the Southern Cross goes by 50 degrees to get very close to Spica. Draw the line from Southern Cross to Spica and then turns 30 degrees anticlockwise and continue for another 30 degrees to reach Bootes Arcturus.)

Turning clockwise by 90 degrees at Spica to leave the Ecliptic and traveling by 30 degrees takes us to a much brighter unmistakable star Bootes Arcturus.

Instead of turning right toward Bootes Arcturus, traveling along the Ecliptic for another 50 degrees take us to a bright star Antares in the Scorpius (Observers from the Southern Hemisphere may also see that Antares is 45 degrees clockwise and 45 degrees distance from the direction of dim Pointer to bright Pointer.).

Figure: Antares is the bright star in the Scorpius constellation which has the shape of a declawed scorpion. Two bright objects on the third top of the photo are planets traveling on the Ecliptic. Northern Celestial pole is from the top left (11 o’clock) direction of the photo.

The stars Spica, Bootes Arcturus, Antares form an arrow-head pointing North.

The midpoint of the great circle arc from Spica to Bootes Arcturus is almost on the Celestial equator. Rotating this arc clockwise by 30 degrees makes its extension goes through both Celestial poles. Northern Celestial pole is 90 degrees from the midpoint and on the side of Bootes Arcturus. Southern Celestial pole is 90 degrees from the midpoint and on the side of Spica.

The internal bisector of the angle formed by (Spica, Bootes Arcturus, Antares) points to the Southern Celestial pole while its rearward extension points to the Northern Celestial pole.

Figure: Photograph of Spica (near the bottom edge), Bootes Arcturus (near the right edge) and Antares (1/8 of the width from the left edge) forming a triangle. Celestial North is at 01 o’clock position (30 degree clockwise from vertical) in this photo. There is a very bright planet (1/2 from left edge, 1/3 from bottom) traveling on the Ecliptic in this photo.

Bright Stars 20 Plus 2

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

5. Visibility of the stars.
Orion constellation, Sirius and its surrounding stars are visible after Sunset. Spica, Bootes Arcturus and Antares are all visible for nearly the whole night in April.

Figure 1: Azimuth and elevation angles of stars for equatorial observers.

Figure 2: Azimuth and elevation angles of stars for observers on 30 degrees North latitude.

Figure 3: Azimuth and elevation angles of stars for observers on 30 degrees South latitude.

6. CAUTION with planets
The Moon and planets travel on the Ecliptic. Observers should take care not to mistake any planet for a navigational bright star.
A planet is always brighter than any star, including Sirius, moves from night to night, and does not twinkle in clear sky.

References.

[1]. tonytran2015, Finding North from unclear sky around New Year, survivaltricks.wordpress.com, Finding North from unclear sky around New Year, posted on 2018, April 05.

[2]. tonytran2015, Finding North and time by stars, survivaltricks.wordpress.com, Finding North and time by stars, posted on August 28, 2015

[3]. , posted on

[4]. The Orion constellation., posted December 26, 2016

[5].The Scorpius constellation., posted January 8, 2017

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The Scorpius constellation

The Scorpius constellation

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.45).

#find North, #finding North, #direction, #by stars, #Scorpius, #Antares, #Sagittarius, #Ara, #navigation, #constellation.

Celestial navigators who do not use declination and right ascension begin their navigation by learning the various bright, easily identifiable constellations in the sky (There are no more than 10 to learn.). The Scorpius is usually chosen to be the second constellation to be learned since it is as large as Orion and is useful when Orion is out of sight.

The Scorpius is a crowded, large Southern constellation of June. Part of it is always seen in the sky of June for the whole night, attains its highest elevation (or altitude) about midnight and is immediately South of the most Southern point of the Ecliptic. Scorpius can be seen on the rising side before sunrise in January, seen for the whole night in May and seen on the setting side after sunset in November.

It has the size of 30 degree (in angle) and has the shape of a hook oriented 55 degree clockwise from the great circle arc through the Celestial poles. Arabian sky watchers see a resembling to the body and tail of a (now declawed) scorpion and gave it the name Scorpius.

The brightest star of Scorpius is Antares but it is so close to the ecliptic that it is often outshone by the Moon and bright planets traveling on the ecliptic. Antares often requires extra care for proper identification. Identifying Antares give a good practice to star identifying.

1. The Scorpius on a Mercator sky-map.

mercator8gc30.jpg

Figure 1: The Scorpio constellation is in the shape of a hook, is close to the ecliptic and one third from the left edge of this Mercator sky-map.

Figure 2: A common Asian scorpion.

The Scorpius has too many stars and its brightest star Antares can even be over-shone by planets wandering near to it. Therefore its identification often requires additional care.

An observer in the Southern hemisphere can check that the hook shaped stinging tail of the Scorpius is just touching the great circle arc (drawn in yellow) through the two Pointers to the Southern Cross.

Figure 3: The Scorpius is seen as a hook in the top left quadrant of this Polar Inversion map of the Southern hemisphere. Its hook shaped stinging tail is just touching the great circle arc (drawn in yellow) through the two Pointers to the Southern Cross.

2. An alternative method of recognizing stars in the Scorpius

Figure 1: Scorpius Sagittarius and Ara are easily recognized together.

I found that it is easier to recognize the bright stars of three constellations Scorpius, Sagittarius and Ara together. They resemble a tree with two side roots rising at right angle from a ground line.

The two brightest stars of all three constellations are Antares and Shaula in the Scorpius.They are separated by 17 degrees in angle. They line up with two other dim stars to form a straight line (delta Scorpius, Antares, Shaula and kappa Scorpius) which is slightly longer.

The South-trailing end of this line continues to be the bisector of a right angle line formed by five stars zeta Sagittarius, Kaus Australis, Shaula, theta Scorpius, alpha Ara.

The line of two brightest stars looks like a tree sticking up at right angle to the ground line formed by dimmer stars in line with alpha and epsilon Ara. The tree has two side roots (Shaula-Kaus Australis. and Shaula-theta Scorpius-alpha Ara) originating from Shaula and each is at 45 degree from the tree trunk.

After the bright stars have been identified, each constellation can be identified using its conventional map as given in [1] and [2].

3. Taking photos of the Scorpius.

The Scorpius is adequately bright and its photos can be taken using a smart phone such as a Samsung Galaxy Note 2 with no extra attachment.

Figure 1: A photo of the Scorpius Constellation taken with a Samsung Galaxy Note 2. This photo was added on 2018Feb26 and has been digitally enhanced.

The Scorpius constellation is in the center of this picture. There are four brightest dots on the top half of this picture. The far right and far left dots are very bright and are two planets traveling on the ecliptic. The planets on the ecliptic sometimes make it hard to identify this constellation. (This added photo was taken on 2018 Feb 26).

Scorpius

Figure 2: Photo of the Scorpius Constellation taken with a Samsung Galaxy Note 2. The original photo was taken prior to 2017Jan09 and has been digitally enhanced.

Scorpius

Figure 2: Another photo of the Scorpius Constellation taken with Samsung Galaxy Note 2. The original photo was taken prior to 2017Jan09 and has been digitally enhanced. There are three bright dots in a straight line at the top of the first photo. The two on the left are two planets on the ecliptic. The third one on the right is delta Scorpius. Antares is the bright dot under the three in line.

4. Easy identification of Scorpius by a slide sky map.

starmap18april0130c.jpg

Figure 1: The Scorpius position by the Mercator slide sky map, with an altitude grid for an observer on 10 deg North (South of India, Thailand, Malaysia, South of Vietnam, the Phillipines, Central America) .

Observers who are not quite familiar with the Scorpius constellation can use the slide sky map described in reference [2] to confirm its identity. The latitude of the observer, time, and North direction are required for identification using a slide sky map. The figure here gives its altitude (elevation) and its orientation at the time of the first photo of the preceding section.

References.

[1]. tonytran2015, Finding North and time by stars in the tropics, survivaltricks.wordpress.com,Finding North and time by stars in the tropics, posted on May 25, 2016

[2]. tonytran2015, Slide Sky-Map for displaying tropical stars, survivaltricks.wordpress.com, Slide Sky-Map for displaying tropical stars., posted on October 7, 2016

[3]. tonytran2015, Finding North and time by stars, survivaltricks.wordpress.com,Finding North and time by stars, posted on August 28, 2015

[4]. The Orion constellation., posted December 26, 2016

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Identifying moderately bright navigational stars.

Identifying moderately bright navigational stars

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. 27).

#find north, #navigation, #survival, #moderate stars, #bright star, #Antares, #Fomalhaut, #direction, #distance, #great circle, #navigation, #stars, #neighbour stars, #sky map

Introduction.

Some navigational stars are only moderately bright although they are in the top 20 brightest stars. Antares and Fomalhaut are two such stars. They are used for navigation from September to November but are not easy to identify among their nearly as bright neighbours. The method for identifying them is to relate them to brighter neighbours which have been identified in previous periods of the year.
(GPS navigation cannot be relied on during periods of uncertainty. Traditional methods of navigation is still a necessary skill.)

Using an identifying map.
Knowing the date or even only the month of a star help locating parts of the sky where it may be found. The map giving distances and angles to its more distinctive neighbours then help its identification.

The maps are to be held such that its shown Celestial pole is pointing close to that actual Celestial pole whether it is in the sky or below the ground. The map is thus to be held in the star direction but oriented either upright or up-side-down.

Examples:

Figure 1: Antares in Scorpii with its neighbours. The centering mark is the Southern Celestial pole.

Figure 2: Fomalhaut with Alpha, Beta Grus and their neighbours. The centering mark is the Southern Celestial pole.

ariessmallc30.jpg

Figure 3: Hamal in Aries and its brighter neighbours. The tail of the inverted Little Dipper in the North is the North pole.

The first two maps make easy the confusing identification process of these two Southern navigational stars for October.

The third map makes easy the identification process of the dim Northern star Hamal in Aries for November.

References.

[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

[2]. tonytran2015, Finding North and time by stars, survivaltricks.wordpress.com, https://survivaltricks.wordpress.com/2015/08/28/finding-north-and-time-by-stars/, posted on August 28, 2015.

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