- #1
swampwiz
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I was reading about the upcoming transit in May, 2019, and this fact seems quite peculiar. Is there some type of resonance?
Why do transits of Mercury only occur in May & November?
- Context: Undergrad
- Thread starter swampwiz
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Discussion Overview
The discussion centers around the occurrence of transits of Mercury, specifically why they only happen in May and November. Participants explore the underlying astronomical mechanics and potential resonances involved in this phenomenon.
Discussion Character
- Exploratory, Technical explanation, Conceptual clarification
Main Points Raised
- One participant notes the peculiarity of transits occurring only in May and November and questions whether there is a type of resonance involved.
- Another participant suggests that the orbital plane of Mercury, when considered against the ecliptic reference, is stable relative to Earth's orbital plane, leading to intersections in May and November.
- A later reply mentions the effect of precession on the orbital nodes of Mercury, indicating that while this may change over time, it occurs over a very long period.
- One participant highlights that the average date for a transit shifts due to the longitude of Mercury's orbital nodes increasing by about 1.1 degrees per century, implying a long-term change in transit timing.
- Another participant concludes that the question has been answered based on the information about the long-term shift of the nodes.
Areas of Agreement / Disagreement
Participants express varying levels of understanding regarding the mechanics of Mercury's transits, with some agreeing on the influence of precession and nodal shifts, while others remain uncertain about the implications of these factors.
Contextual Notes
The discussion touches on the complexities of orbital mechanics and the long-term changes in the timing of transits, but does not resolve all aspects of how these factors interact.
Who May Find This Useful
Individuals interested in astronomy, particularly those curious about planetary transits and orbital dynamics, may find this discussion relevant.
- #2
DaveC426913
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Have a read here:
https://en.wikipedia.org/wiki/Transit_of_Mercury
And see if any of your questions aren't answered.
https://en.wikipedia.org/wiki/Transit_of_Mercury
And see if any of your questions aren't answered.
- #3
swampwiz
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DaveC426913 said:
That's the article I had read. It doesn't explain it clearly; however, I suppose that if the orbital plane of Mercury were considered to be the ecliptic reference, and that plane is stable with respect to the Earth's orbital plane, then as it stands, these planes cross in May & November (this would seem to be something that would change with precession, but that seems to have a very long time period?), essentially like draconic nodes necessary for the Earth-Moon-Sun syzygy to be an eclipse. Is this the reason?
- #4
DaveC426913
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"... The average date for a transit increases over centuries as a result of the longitude of the nodes of Mercury's orbit increasing by about 1.1 deg per century..."swampwiz said:
- #5
swampwiz
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DaveC426913 said:"... The average date for a transit increases over centuries as a result of the longitude of the nodes of Mercury's orbit increasing by about 1.1 deg per century..."
So that means it would take about 3K years to move a month away. OK, this question has been answered!
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