Point A is the centre of the Earth, Point L is London, Point M is the moon, Line AB is the equator, ∠ D is the lunar declination, ∠ G is the geographical latitude of London(+51.5°). Line L represents where the place the moon appeared at “the centre of the Earth”. ∠ Φ is thus the lunar parallax.
Fig. 14 Determining Distance
Our goal is to find the length of LM. Θ can be calculated by subtracting ∠ D from ∠ G,
51.5°- 15.89° = 35.61°. Line MA is parallel to line L, thus ∠ LMA = Φ . The length of line GL is equal to the radius of the Earth: 6,371 km. Using the sine relation on triangle LAM:
The distance to the moon is 370000 km.
Conclusion
Parallax calculation is one of the most important techniques used by astronomers, and congratulations, now you know the simple mathematical techniques (essentially trigonometry) used to calculate the distance from earth to moon (Lunar Parallax), the distance from earth to the sun (Solar Parallax), and the distance from earth to any star (Stellar Parallax).
Parallax is also seen in daily life: you read values from a measuring cylinder to avoid parallax, your eyes can see in three dimensions by using parallax, rangefinder cameras uses parallax to determine distance, even birds and chickens depends on motion parallax for depth perception by bobbing their heads while walking! The numerous applications of parallax make parallax a must know topic for you. Next time you walk to Tesco you will be able to explain the effects of parallax for your friend and list the numerous applications of parallax in the astronomical field, instead of exposing your stupidity (no offence) by saying “I never knew that birds fly slower than fence posts do”.
Bibliography: 1. "Parallax". 2017. En.Wikipedia.Org . https://en.wikipedia.org/wiki/Parallax.
2. "Stellar Parallax". 2017. En.Wikipedia.Org . https://en.wikipedia.org/wiki/Stellar_parallax. 3. "Parallax: Distance". 2017. Khan Academy . https://www.khanacademy.org/partner- content/nasa/measuringuniverse/measure-the-solarsystem/a/parallax-distance. 4. Lucas, Jim. 2015. "What Is Parallax?". Space.Com . https://www.space.com/30417-parallax.html. 5. Kaufmann, William J. 1991. Universe . 1st ed. New York: W.H. Freeman. 6. Khan, Salman. 2017. Stellar Parallax . Video. https://www.khanacademy.org/science/cosmology- and-astronomy/stellar-life-topic/stellar-parallax-tutorial/v/stellar-parallax: Khan Academy. 7. Pogge, Richard. 2017. "Lecture 5: Stellar Distances". Astronomy.Ohio-State.Edu . http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit1/distances.html.
Made with FlippingBook - professional solution for displaying marketing and sales documents online