- #1
lighthouse1234
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Why is it that I can still use my 10 year old planisphere, if the stars are in motion?
Are the stars of the constellations stationary?
- Context: High School
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Discussion Overview
The discussion revolves around the apparent motion of stars in constellations and the reasons why they seem stationary despite being in motion. It touches on concepts of relative motion, astronomical distances, and the perception of movement over time.
Discussion Character
- Exploratory
- Conceptual clarification
- Debate/contested
Main Points Raised
- Some participants suggest that the relative positions of stars change very slowly, making them appear fixed over a human lifetime.
- Others argue that while stars are indeed moving, their vast distances mean that their motion is not perceptible without precise measurements.
- A participant mentions that the nearest stars can move back and forth against the background due to Earth's orbit, which is a method used to measure distances to nearby stars.
- Another participant provides an analogy comparing the perception of a train moving slowly from a distance to the way stars appear to move slowly due to their great distances.
- One participant notes that the star 61 Cygni has a measurable proper motion, illustrating that some stars do have noticeable movement, albeit very small compared to their distances.
Areas of Agreement / Disagreement
Participants express differing views on the perception of star motion, with some emphasizing the slow change in relative positions and others highlighting the actual movement of stars. The discussion remains unresolved regarding the implications of these observations.
Contextual Notes
Limitations include the dependence on observational perspectives and the scale of distances involved, which affect how motion is perceived. The discussion does not resolve the complexities of measuring stellar motion.
- #2
Baluncore
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Because the relative positions of the "fixed stars" change very slowly, so you do not notice it in your lifetime, unless you are an astronomer.
- #3
lighthouse1234
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Someone wrote this to me: From that moving position these 'fixed stars' seem to be stationary,
hence are actually moving, even if they seemingly do not.
hence are actually moving, even if they seemingly do not.
- #4
Baluncore
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Is that a question?
As the Earth orbits the Sun, the relative position of the nearest stars, move back and forth every 6 months, against the distant background. That is how we identify and measure the distance to nearby stars.
As the Sun moves through and with the galaxy, the relative positions of the fixed stars gradually move against the distant background.
From what moving position?lighthouse1234 said:
As the Earth orbits the Sun, the relative position of the nearest stars, move back and forth every 6 months, against the distant background. That is how we identify and measure the distance to nearby stars.
As the Sun moves through and with the galaxy, the relative positions of the fixed stars gradually move against the distant background.
- #5
FactChecker
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The stars in constellations are so far away that they can be moving tremendously fast and we will not be able to notice it with the naked eye in our lifetime. The nearest star in Orion is Bellatrix, which is 250 light years away. A light year is 5.8 trillion miles. The farthest star in Orian is Alnilim, which is 1360 ly away. So the change in angle will be small unless/until they move very far sideways or up and downlighthouse1234 said:
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Vanadium 50
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There's a source!lighthouse1234 said:
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Vanadium 50
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The visible star with the largest proper motion is 61 Cygni. In 10 years, it moves about 2-1/2 arc-seconds. That's 0.15% of the apparent size of the moon.
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Drakkith
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If I stand far away from the train tracks near my house and watch a train go by, the train appears to move very slowly. If I hold my thumb up it takes about a second for the train to 'cross' behind it. But if I stand next to the tracks the train will cross behind my thumb in a small fraction of a second.lighthouse1234 said:
The same is true for stars. They may be moving very quickly relative to us, but they are so far away that they don't appear to be moving hardly at all.
- #9
berkeman
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"There's that guy again, trying to hitch a ride on our train..."Drakkith said:
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