[Astronomer]

I've scoured the forums, and while I've seen multiple threads dedicated to the planets, I haven't seen this particular phenomenon addressed.
Indeed, most of the planetary questions have gone unanswered, so I doubt to get a satisfactory response, but perhaps some of you FE'rs can share your opinions and shed some light (pun intended) on this for me.

I was wondering (I know there are 20 different models) how the flat earth model(s) account for the phases of the planets.
The Helioentric model of the solar system accounts for them perfectly. The only two planets to exhibit full phases (similar to our own moon) are the two planets closer to the sun than us, Mercury and Venus. In fact, we can observe these inner 2 planets transit between earth and the sun. Mercury will transit in November of this year, while Venus unfortunately won't transit again until 2117.
The outer planets do not exhibit these full phases, nor do they transit between the earth and the sun.
It's relatively straightforward geometry from a heliocentric standpoint. Thoughts?

[somerled]

Inner planets orbit the sun which is local and circles the earth . Outer planets are further away but not part of the starry firmament ,which is further still . The sun transits across these planets ( at opposition I think the term is ).

Tycho Brahe's geocentric model explains this .

Other evidence supporting this view - syzygy effects on pendulums caused any"solar system" bodies . Plus the fact that stars twinkle , planets do not .

[Astronomer]

Brahe revolutionized astronomy, and the Tychonic model made perfect sense in his time, and for over a hundred years afterward. Using Tycho’s revolutionary data, Kepler deduced that the movement of the planets were eclipses rather than circles.
However, the main objection to the copernican model during his time, apart from religious and philosophical arguments, was the absence of observational stellar parallax.
Proponents of the copernican model argued that the stars were too far away to observe the parallax with the instruments of their day, and it turns out they were correct. Stellar parallax was first observed in the mid 1800’s by German scientist Friedrich Bessel.

Stellar parallax definitively proves that the earth is moving around the sun, in relation to the stars, and debunks Brahe’s heliogeocentric model.

[Astronomer]

Concerning the fact that stars twinkle while planets don’t. The reason for this is simple. Stars are so far away that we can’t resolve their disc, and since the light is seemingly emitted from a pinpoint, it’s quite susceptible to disturbances in the atmosphere; refraction. Planets don’t have this problem, as they are easily resolved and aren’t as susceptible to this refraction. This fact however doesn’t pertain to the argument.

As far as syzygy goes, I’m afraid you’re going to have to be more specific, and I don’t see how it either relates to the OP.

[dirtysnowball]

Plus the fact that stars twinkle , planets do no

The twinkle or scintillation of light is caused by the atmosphere. Since the light from both the stars and the planets passes through the atmosphere on its way to a detector (whether that is the human eye or a imaging sensor) it stands to reason that both are subject to this effect.

However as astronomer mentions, a star image is a true point source of light (i.e. the star image is smaller or less than the diffraction limit of the telescope) whereas a planetary disk does have a measurable diameter, albeit in arc seconds. That lessens the effect of 'twinkling' on a planetary disc and so to the naked eye the planets appear not to twinkle.  If you look at an out of focus planetary image in a telescope you will definitely see the twinkling effect happening.

Concerning the mention of syzygy... in astronomy at least this means an alignment of, such as in conjunction or opposition.  The inner planets of Mercury and Venus will experience conjunction when either the planet comes in line with the Sun and the Earth (inferior conjunction) or when the Sun comes between the planet and the Earth (superior conjunction). Mercury and Venus never reach opposition.

The outer planets (Mars outwards) reach opposition when the Earth comes directly in line with the Sun and the planet or conjunction when the Sun comes directly between the planet and the Earth. In the case of the former the planet is visible all night and in the case of the latter the planet passes from the evening sky into the morning sky.

Overall it is a LOT easier to explain the observed planetary events and positions by considering the heliocentric model with the Earth 3rd out from the Sun than it is to take the Earth as a plane with the other planets all orbiting around a Sun which collectively exist above said plane.  How can that work?

How this relates to pendulums on Earth exactly I am unsure. So perhaps you could explain.

Stellar parallax definitively proves that the earth is moving around the sun, in relation to the stars, and debunks Brahe’s heliogeocentric model.Stellar parallax definitively proves that the earth is moving around the sun, in relation to the stars, and debunks Brahe’s heliogeocentric model.

Agreed.