Why do transits of Mercury only occur in May and November?

  • Level: Undergrad 
  • Thread starter Thread starter swampwiz
  • Start date Start date
  • Tags Tags
    Mercury
Join the discussion
Registration is free. Start your own thread to ask a follow-up.
Sign up Log in
4 replies · 2K views
swampwiz
Messages
567
Reaction score
83
I was reading about the upcoming transit in May, 2019, and this fact seems quite peculiar. Is there some type of resonance?
 
Astronomy news on Phys.org

Discussion

DaveC426913 said:
Have a read here:
https://en.wikipedia.org/wiki/Transit_of_Mercury
And see if any of your questions aren't answered.

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?
 
swampwiz said:
...this would seem to be something that would change with precession, but that seems to have a very long time period?...
"... 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..."
:wink:
 
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..."
:wink:

So that means it would take about 3K years to move a month away. OK, this question has been answered!