How stellar aberration was quantified in the early days

In summary, the conversation discusses exercise 3-9 in "Spacetime Physics" which concerns the aberration of starlight. The question is how to measure the effect of aberration since the background of stars also shifts. The answer is to measure the angle between the north celestial pole and the position of the star, which shifts depending on the time of year. However, there is uncertainty about how to quantify the aberration in the direction perpendicular to this. The pdf provided states that Bradley did not record the East-West aberration due to practical difficulties. The motion of the whole sky towards the direction Earth is moving can be detected in the north-south direction by referencing celestial north, but the absolute reference for the East-West
  • #1
Gene Naden
321
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I am working through "Spacetime Physics" and encountered exercise 3-9, which concerns aberration of starlight. They ask the following question: "Since the background of stars also shifts due to aberration, how can the effect be measured at all?"

I got part of the answer. You measure the angle between the north celestial pole and the position of the star. It shifts depending on what time of year it is. That takes care of one component (I think). But I am puzzled as to how you quantify the aberration in the direction perpendicular to this.

Well in the pdf https://www.colorado.edu/physics/phys2170/phys2170_fa06/downloads/stellar_aberration.pdf it says that Bradley did not record the East-West aberration due to practical difficulties. So that perhaps answers my question.
 
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  • #2
The whole sky "moves" towards the direction Earth is moving to (as seen from the Sun), and this direction changes over time. This distorts the pattern of the stars with a yearly cycle.
 
  • #3
The motion in the north-south direction can be detected by reference to celestial north. How is the motion in the East-West direction detected. What is the absolute reference for east-west direction?
 
  • #4
mfb said:
The whole sky "moves" towards the direction Earth is moving to (as seen from the Sun), and this direction changes over time. This distorts the pattern of the stars with a yearly cycle.

The aberration affects the stars around the star you are observing, so you cannot simply compare the star to the stars around it.
 
  • #5
With stars nearby you won't see a strong effect, with stars at larger angles you will see one. The angle between stars at 90 degree angles (e.g. one in "forward"/"backward" direction, one in "outwards"/
inwards" or "upwards" or "downwards" direction 6 months apart) varies by up to 40 arcseconds over a year.
 
  • #6
Thank you
 

1. What is stellar aberration?

Stellar aberration is a phenomenon in which the apparent position of a star appears to shift when viewed from different points in the Earth's orbit due to the finite speed of light and the motion of the Earth.

2. How was stellar aberration first observed?

Stellar aberration was first observed in the early 18th century by astronomer James Bradley, who noticed that the positions of stars appeared to shift slightly throughout the year. He initially attributed this to the Earth's orbital motion, but later experiments confirmed that it was actually due to the speed of light.

3. How was stellar aberration quantified in the early days?

In the early days, stellar aberration was quantified using simple trigonometry and measurements of the angle of the star's apparent shift. This allowed scientists to calculate the speed of light and the Earth's orbital velocity.

4. What instruments were used to measure stellar aberration in the early days?

The main instruments used to measure stellar aberration in the early days were telescopes and precise clocks. Telescopes were used to observe the stars and measure their position, while precise clocks were used to record the time of observation.

5. How did the understanding of stellar aberration contribute to the development of astronomy?

The understanding of stellar aberration played a crucial role in the development of astronomy by providing evidence for the heliocentric model of the solar system and helping to refine our understanding of the speed of light. It also paved the way for more precise measurements and observations in astronomy, leading to further advancements in the field.

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