Post by StarVega on Oct 11, 2018 21:48:16 GMT
I mentioned Venus transiting the sun in another thread. We have a Mercury-sun transit next year, 11 November 2019.
* Mercury's heliocentric north node: 18°32 Taurus
The sun and Mercury must be on Mercury's helio nodes in order for this transit of the sun to occur.
"Mercury transits occur just 13 times per century, on average. They're so rare because the innermost planet's orbit is inclined by about 7 degrees compared to that of Earth, so Mercury, the sun and our home planet just don't line up all that often. [Mercury’s 2016 Transit of the Sun: A Rare Sight (Video)]
Mercury completes one lap around the sun every 88 days, so the little planet crosses the plane of Earth's orbit every 44 days — once while moving "up" and again while coming back "down." These points of intersection are called nodes.*
These nodes line up with the sun from Earth's point of view just twice per year, once in May and once in November. If Mercury happens to be at the node at either of these times, Earth observers see a transit. (All Mercury transits occur within a few days of May 8 and Nov. 10.)
Mercury's orbit is elliptical, so May transits and November transits are different beasts.
"During November transits, Mercury is near perihelion and exhibits a disk only 10 arcseconds in diameter," NASA officials wrote in a description of planetary transits, which are basically just mini-eclipses. (Perihelion refers to an orbiting planet's closest approach to the sun; aphelion is its most distant position from the star.)
"By comparison, the planet is near aphelion during May transits and appears 12 arcseconds across," the officials added. "However, the probability of a May transit is smaller by a factor of almost two. Mercury's slower orbital motion at aphelion makes it less likely to cross the node during the critical period."
Read more:
www.space.com/32806-why-mercury-transit-of-sun-rare-event.html
Mercury completes one lap around the sun every 88 days, so the little planet crosses the plane of Earth's orbit every 44 days — once while moving "up" and again while coming back "down." These points of intersection are called nodes.*
These nodes line up with the sun from Earth's point of view just twice per year, once in May and once in November. If Mercury happens to be at the node at either of these times, Earth observers see a transit. (All Mercury transits occur within a few days of May 8 and Nov. 10.)
Mercury's orbit is elliptical, so May transits and November transits are different beasts.
"During November transits, Mercury is near perihelion and exhibits a disk only 10 arcseconds in diameter," NASA officials wrote in a description of planetary transits, which are basically just mini-eclipses. (Perihelion refers to an orbiting planet's closest approach to the sun; aphelion is its most distant position from the star.)
"By comparison, the planet is near aphelion during May transits and appears 12 arcseconds across," the officials added. "However, the probability of a May transit is smaller by a factor of almost two. Mercury's slower orbital motion at aphelion makes it less likely to cross the node during the critical period."
Read more:
www.space.com/32806-why-mercury-transit-of-sun-rare-event.html
* Mercury's heliocentric north node: 18°32 Taurus
The sun and Mercury must be on Mercury's helio nodes in order for this transit of the sun to occur.
