Starship Asterisk*

MarkBour wrote: ↑Wed Nov 20, 2019 5:10 pm Thanks for the reply, Chris. Several items of helpful info.

One in particular would seem to rule out the "interstellar medium" idea I put forth.

Chris Peterson wrote: ↑Tue Nov 19, 2019 11:15 pm
... I doubt that the interstellar medium, or anything lying between stars and us, represents a measurable component of variability. There's no correlation between the light curves of very close stars, as you'd expect for something in the interstellar medium.

I think you're saying that there's no correlation between the variability for star light curves and their distance from us (in our galaxy, on the scales we're considering). I that correct? If that has been looked at and it has been found that there is no such correlation, that's a key fact.

Chris Peterson wrote: ↑Wed Nov 20, 2019 5:58 pm ...
If variation was caused by intervening material, you'd expect to find correlation in the light curves of stars that are located close together in the sky, regardless of their actual distances (although stars that were at the same distance would correlate better... such as double stars). I know that the light curves of double stars don't show correlation.

Chris Peterson wrote: ↑Thu Nov 14, 2019 4:31 pm

BillLee wrote: ↑Thu Nov 14, 2019 3:23 pm Can somebody explain why there will only be 14 transits in the 21st century. Seems to me that every time Mercury goes around the sun that it would be visible against the sun as a backdrop. I cannot envision the geometry that would limit that to only 14 in 100 years.

Mercury's orbit doesn't lie on the same plane as Earth's orbit. Most of the times that Mercury lies between the Earth and the Sun it is tilted enough above or below Earth's orbital plane that it isn't passing in front of the Sun's disc. It's the same reason we don't have a solar eclipse and a lunar eclipse every month (because the Moon's orbit around Earth isn't coplanar with Earth's around the Sun).