Measuring the distance to stars for A Level physics - parsec

-

 

parsec - distance to stars

When it comes to distances involved in the objects in space, three major units are used. They are,
  • astronomical unit
  • light-year
  • parsec
Astronomical unit - AU
This is the average distance between the Sun and the Earth.
1AU = 150 million km = 1.5 x 1011 m
The astronomical unit, AU,  is used to express the distance between the Earth and the other planets in our solar system.

Light-year - ly 
The distance travelled by light in one year is called a light-year.
1 light-year = 3 x 108 x 3600 x 24 x 365 = 9.46 x 1015 m

parsec -pc
The distance at which 1AU subtends an angle of 1 arcsecond is called a parsec.
1 arcsecond - (1/3600)°
tan (1 arcsecond) = 1AU/1pc
1 pc =  1AU x tan(1 arcsecond)
1pc = 1.5 x 1011 x tan(1 arcsecond)
1pc = 3.1 x 1016 m or 1 pc = 3.26 ly

You can calculate the angle in arcseconds and pc with the following simulation:







Comments

Post a Comment

Popular posts from this blog

Phase Difference between Two Points on a Wave and Path Difference Explained - interactive

-
Image
  In the above animation, five points on the wave are considered for the explanation.  The fully interactive applet is given below for you to practise. The phase of a point implies its direction of vibration on a wave. For example, both points A and E vibrate exactly the same way are said to be in phase: when A goes up so does B; the phase difference is either 0 0 or 360 0 . If you consider the motion of points A and C, on the other hand, when A goes down C goes up or vice versa. Therefore, A and C are said to be out of phase; the phase difference is 180 0 . That means the phase difference between two points on a wave - or two waves for that matter - can take any value between 0 0 and 360 0 .  The phase difference between points A and B, for instance, is 90 0 . From the above examples, it is clear there is a connection between the path difference between two points - or two waves - and phase difference. It is as follows: Phase difference = (path difference / wavelength) x 360 φ = x
Read more

Frequency Amplitude and Wavelength of a Transverse Wave - simulation

-
Image
Waves A wave carries energy from a point to another point in a medium / vacuum without the movement of the particles along with it. In the above animation, the wave moves from the left to the right; the particles, however, just vibrate vertically without moving along with the wave. Transverse Waves If the direction of the wave is perpendicular to the vibration of particles, it is called a transverse wave. E.g. Water waves, radio waves, microwaves Amplitude The maximum displacement of a particle in a wave is called amplitude. Intensity / loudness The intensity / loudness of a wave is proportional to the square of the amplitude. The greater the amplitude, the greater the intensity / loudness. Amplifier This is what an amplifier does: it increases the amplitude of an input signal, which in turn leads to the increased loudness or intensity. Frequency  - f The number of cycles of a wave that passes through a point in a unit time is called frequency. Wavelength  - λ The distance between
Read more