My star selection contains the brightest and most noticeable stars in Orion. I selected: Betelgeuse, Bellatrix, Mintaka, Alnilam, Alnitak, Rigel and Saiph. See the star map below
Astrophysics is the marriage of physics and astronomy, and one key property of stellar objects is their distance from the earth. For thousands of years, the parallax method has been used to measure distances on earth. See the interesting online article “Distance: A History of Parallax” by B.J. Gillot. [http://www.bgfax.com/school/distance_history.pdf]
Parallax is the apparent shifting of an object against a distant background when viewed from two different positions.
This phenomenon can be used for distance measurements of terrestrial and celestial objects. The stars form a pattern in the sky, and our view of the pattern depends on where and when we view the stars. We can use parallax to determine the distance of a near star against the background of more distant stars.
We need two viewpoints as far apart as possible if we are to see the greatest change in a star's apparent position relative to more distant stars. The longest baseline we can establish between two viewpoints is the opposite extremities of the earth’s orbit about the sun, a distance of two astronomical units (2 AU). This occurs after the earth travels about the sun for six months.
Before the invention of the telescope, the lack of noticeable parallax in stellar motion suggested that the earth was stationary and thereby the center of the universe. After the invention of the telescope, the discovery of parallax helped prove that the earth is in motion and that the sun is our solar system.
Although I used a spreadsheet to convert milli-arc-second (mas) to light-years (ly), the following illustrates the calculations for Betelgeuse.
First, convert milli-‐arc-‐seconds (mas) to arc-‐seconds (as):\(6.55mas\left(\frac{1as\ }{1000mas}\right)=0.00655as\)
Then calculate the distance in parsecs (PC): \(d\approx\frac{1}{p}=\frac{1}{0.00655as}=152.67pc\)
Finally, calculate the distance in light years (ly):\(152.67pc\left(\frac{3.26ly}{pc}\right)=497.71\ 1y\)
Here is a screenshot of my result from a spreadsheet Logger Pro 8.3.4 for the Mac computer graphing software by Vernier. See http://www.vernier.com/
A constellation is an area of the sky containing a pattern of stars named after a particular object, often an animal or person. The word ‘constellation’ comes from Latin, and means “stars together.” [See “In Quest of the Universe” by Karl Kuhn (Second Edition, West Publishing Company, second edition), pages 16 and 17.] The stars in the recognizable pattern appear near each other in space (in their angular separation as seen from earth), but the stars in the constellation may or may not be in physical proximity.
In a stellar cluster, the stars are close enough to interact by gravitational forces. In astronomical terms, they are physically close. There are clusters of stars and clusters of galaxies as well as super-‐clusters. There is no well-‐defined value to the proximity of stars and galaxies when they are called clusters and yet the term has a significant meaning. [See “Star Clusters” pages 1-‐6 in Encyclopedia of Astronomy and Astrophysics, http://eaa.crcpress.com/] In general, a cluster of stars is created by the collapse of the same gas cloud and the stars interact by gravity.
Moreover, there are two types of star clusters: globular clusters are tight groups of hundreds of thousands of very old stars, and open clusters generally contain less than a few hundred members and are often very young. This distinction is not relevant to my study. [http://www.sciencedaily.com/articles/s/star_cluster.htm]
The distinction here is between the appearance and the true location of stellar objects. A pattern of stars may consist of stars that are physically (in astronomical terms) far away from each other, but because of our perspective, they appear to form a close recognizable pattern, as if they are centrally located.
Although there are 88 recognized constellations in the night sky I selected one that is easily recognizable with the naked eye and is familiar to me and popular throughout history. [http://starchild.gsfc.nasa.gov/docs/StarChild/questions/88constellations.html]
Orion is by far the most famous seasonal constellation. No other is more distinct or bright than this northern winter constellation. The famous Orion's Belt makes the ‘hunter’ easy to find in the night sky. I, therefore, choose a selection of stars from Orion as the object of my research.
I feel magic in the stars, in the universal when pondering the night sky. the recognizable patterns of the constellations feed my imagination with wonder. I was fortunate to study the astrophysics option in physics class and, when told to research an IA exploration of my own interest, I could only turn my attention to the stars once more, this time in the daylight. I wanted to learn more about my constellation friends, the stars of Orion.
This exploration establishes how some of the stars in the constellation Orion are related to one another in terms of physical proximity. The distinction between the organization of the stars of a constellation (a mere appearance or pattern seen from the earth) and that of the actual locations of the stars within our galaxy is made. My research question asks “Are the stars in the constellation Orion also in the same cluster of neighbouring stars?”
My method to answer this was to select a number of the stars in Orion and then use an online database to find the parallax angle for each of the selected stars. Then I used a spreadsheet to calculate the distance to each star from the earth. Both a bar graph and a bubble graph are used to illustrate my conclusions. My results are then compared to distances found in other scientific databases.
While viewed as a constellation, the stars of Orion are grouped near one another, yet I found that some of the stars are indeed in the same cluster (in the same relative position in our galaxy) while others are not Orion is made out of many clusters.
The parallax method is useful for relatively close stellar objects; it is often quoted as adequate up to a distance of 326 light-years, that is, angles are measurable down to about 0.01 arc-seconds, where 1/3600 of degree errors and uncertainties increase as distance increases because angles get smaller. Diploma Programme” by Gregg Kerr and Paul Ruth, 3rd edition, IBID Press, page 368.] Although the two observational positions of the earth relative to the sun for measuring parallax is over a period of 6 months, the parallax angle “p” is measured at one-‐half this displacement, just one astronomical unit (AU). The distance from the star to the sun is d and so tanp=1AUd. When d >>1AU and the shift in the star’s image is measured in seconds of arc, the stellar parallax p defines the distance d as d=1p. The unit of distance d is the parsec (pc). The name ‘parsec’ represents the parallel angle of one second.
When an American 10¢ circular coin (diameter 17.9 mm) is 1.6 km away, it subtends an angle of one arc-‐second. This separation, of course, is not visible to the naked eye. In my work, I converted parallax to distance and then to units of light-‐years. I used the conversion factors listed on page 3 in the IB publication of March 2007 called Physics First Examination 2009 Data Booklet.
My exploration used parallax measurement data found in the database The Digital Library for Physics and Astronomy published online by the Harvard-‐Smithsonian Center for Astrophysics. This is a database used by professional astronomers. The website of The SAO/NASA Astrophysics Data Base System is http://adswww.harvard.edu/ and links from here connect to the actual data.
The search engine was: http://simbak.cfa.harvard.edu/simbad/
The image below shows the online database. Requests for information can be entered either under basic search or by identifier, depending on how much one already knows. I used the basic search, as shown below.
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Social and historical dimension
Orion, known as The Hunter, has been identified over thousands of years by many different cultures. Orion is among the constellations to work its way into classic texts. It is mentioned in the Bible and the ancient Greek stories of the Iliad and the Odyssey. [“Backyard Guide to the Night Sky” by Howard Schneider (National Geographic Publication, pages 214 and 215)]