by tonytran2015 (Melbourne, Australia).
#find North, #direction, #by stars, #Orion, #Sirius, #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 Orion is usually chosen to be the first constellation to be learned. The Orion is a bright, easily identifiable constellation of December. It stays in the sky of December for the whole night, attains its highest elevation (or altitude) about midnight and is right on the Celestial equator.
It has the size of 30 degree (in angle) and has the shape of a waisted rectangle. Western sky watchers see a resembling to man in an armor vest and gave it the name Orion. Pacific sky watchers see its two brightest diagonal stars as the ends of a large stick in the sky.
It is never blinded by the Moon or any bright planet as the ecliptic is well away from it. As it is quite bright and has easily identifiable shape, it is usually used as the base (anchor marks) to start locating other stars.
1. The Orion on a Mercator sky-map.
Figure 1: The Orion constellation is right on the Celestial Equator and one third from the right edge of this Mercator sky-map.
The three dim stars in a straight line starting from the waist band and almost at right angle to it (not shown in this simplified Mercator sky map) are called the Dagger stars. The Dagger is at right angle to the Celestial equator and points along a great arc in the North to South direction on the Celestial sphere.
Rigel or Beta Orionis is bright star at the South leading corner of the waisted rectangle. Betelgeuse is bright star at the North trailing corner of the waisted rectangle. Bellatrix is a less bright star on the North leading corner of the rectangle.
Rotating the line Betelgeuse – Rigel by 90 degree in the anti-clockwise direction gives the line Betelgeuse – Aldebaran, (Aldebaran is also called alpha Tauri).
Extending the line Bellatrix-Aldebaran by another 50% makes it reaches Pleiades group of stars (not shown on this simplified Mercator sky map). This group has millions of stars fitting within an area as small as the area of the Moon (The area is equal to that of a fingernail on a fully extended arm). Most people can see a brush shape made of 7 brightest stars of this group.
On the trailing side of Orion lies the brightest star in the sky. It is Sirius. Rigel -Betelgeuse – Sirius form an almost equilateral triangle on the trailing side of the line Rigel – Betelgeuse.
Betelgeuse is the star of December 20th and the December solstice occurs on the 21st of December, on the following night .
The night when the brightest star Sirius attains its highest altitude at midnight is the first night of a new (Roman) calendar year (Is it a coincidence?).
2. Taking photos of the Orion.
Figure 2: Photo of the Orion Constellation taken with a Samsung Galaxy Note 2. The original photo has been digitally enhanced.
The Orion is quite bright and photo can be taken using a smart phone such as a Samsung Galaxy Note 2 with no extra attachment.
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