The Southern Cross Pointer stars

 

The Southern Cross Pointer 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.111).

by tonytran2015 (Melbourne, Australia).

#find North, #finding North, #navigation, #alpha Centauri, #Agena, #Southern Cross, #pointers, #constellation, #Scorpius,

The Southern Cross Pointer Stars.

Celestial navigators who do not use declination and right ascension begin their navigation by learning the various bright, easily unmistakable constellations in the sky (There are no more than 10 to learn beginning with Orion constellation. and Scorpius constellation.). In the Southern Hemisphere, the Pointers to Southern Cross constellation are next to be learnt as they are very bright and most easy to identify.

The two Pointer stars are two very bright stars (alpha Centauri and Agena) in the Southern Celestial hemisphere. They are very useful as they help identifying nearby navigational stars and consequently finding Southern Celestial pole for navigation.

These two bright stars are circumpolar and are both 30 degrees from to the Southern Celestial pole. They are seen late night in February, all night in May, early night in September.

Inhabitants of Southern hemisphere need only to identify Alpha Centauri (brighter star of the pair), Agena (dimmer star of the pair), and Achernar in the clockwise direction (all at 60° South declination) to find the Southern Celestial pole which is at the center of the circle of 30 degrees in radius through these three stars. Achernar is almost 60 degree from the Pointers (alpha Centauri, Agena) and is opposite them across the Southern Celestial Pole.

Figure: Pointer stars pointing to the Southern Cross on a Polar Skymap for Southern hemisphere.

Extending the line alpha Centauri-Agena (from brighter to dimmer Pointer) by 8 degrees takes us to the Southern Cross Constellation. Then turning clockwise by 50 degrees and extending by an additional 50 degrees takes us to the very bright Canopus star which is nearly 40 degrees from the Southern Celestial pole.

In the opposite direction, extending the line Agena-alpha Centauri (from dimmer Pointer to brighter Pointer) by about 30 degrees takes us to the stinger tail of the large, distinctive Scorpius constellation (this line goes on for another 40 degrees to reach the bright tropical star Altair). From the direction of the line Agena-alpha Centauri (from dimmer to brighter Pointer) turn clockwise by 50 degrees and travel by about 45 degrees from alpha Centauri takes us to the moderately bright star Antares at the heart of the Scorpion.

Figure: Locating an individual star in a crowded area is easily carried out using a folded piece of cardboard: The folding line is aimed at the first known star, one cardboard flap is aligned to contain the second known star. The other flap is then opened to the required angle (marked 1) and the angle to the target star (marked 2) can be read.

2. The Southern Cross.

The Southern Cross is a useful navigational constellation. Its long axis goes through the Southern Celestial pole (which is also nearly on the bisector of the Pointer Stars and is also nearly on the line through Sirius and Canopus) in one direction and goes through the Northern Celestial pole in the opposite direction.

Turning slightly by 20 degrees anticlockwise toward the trailing’ side (Eastern side) from this direction to the Northern Celestial pole and travel by a distance of about 50 degrees from the Southern Cross takes us to the bright star Spica. Turning more anticlockwise towards the Eastern side by an additional 15 degrees from that direction and traveling an additional distance of about 30 degrees takes us next to the very bright star Bootes Arcturus (The direction from Spica to Bootes Arcturus is pointing about 25 degrees to the trailing side, Eastward, from the direction of a great circle arc toward the Northern Celestial pole.).

3. The dates of Pointers to Southern Cross.

Figure 1: The dates of Agena and alpha Centauri from the table of star dates.

The Pointer stars are seen in late night in February, all night in May, and in early night in September.

4. Taking photos of the Pointers.

Figure 1: The Pointers and Southern Cross Constellation are in the lower right quarter of this phpto taken with a Samsung Galaxy Note 2. The original photo has been digitally enhanced.

The Pointers and Southern Cross constellation are adequately bright and their photos can be taken using a smart phone such as a Samsung Galaxy Note 2 with no extra attachment.

The Pointers and 3 corner stars of the vertical Southern Cross are seen on the bottom right of the above two pictures. The dimmer fourth stars of the Southern Cross can be seen in the second photo. Antares is the bright star near the middle of the left border of the second picture. Antares and the front part of the Scorpius constellation are located near the center of the left border of the second picture (The very bright dot near the upper left corner of the picture is a planet.).

Figure 2: Photos of the Pointers and Southern Cross Constellation taken with a Samsung Galaxy Note 2. The original photos have been digitally enhanced.

The two bright Pointers are seen on the bottom right of this picture 2. The two brightest spots on the left half of this picture are two planets traveling on the Ecliptic. Antares is the bright star near the middle of the half left of this picture. Vertically above Antares is the front part of the Scorpius constellation. Vertically below Antares is the bright stinging tail of the Scorpius.

Figures 3: Photo of the Scorpius Constellation taken with a Samsung Galaxy Note 2 at the same time. The original photos have been digitally enhanced.

The Scorpius constellation just mentioned is captured in the center of the third photo. There are four brightest dots on the top of the 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 confusing the identification of the stars at the front of this constellation.

References.

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

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

[3].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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