Starlight Measurements to Size Up a Planet

Overcoat writes "NASA scientists have used a technique called 'astrometry' to determine the size of a planet orbiting Gliese 876, a star 15 light years away from our solar system. By measuring tiny changes in the 'tilt' of light emitted from the star, changes which were caused by the force exterted by the orbiting planet known as Gliese 876b, the scientists were able to determine that the planet is the size of a golfball. Just kidding: the planet's a whopper, coming in at between 1.89 and 2.4 times the size of Jupiter. This marks the first time astrometry, usually used to measure the distance between stars, has been used to measure a planet."

Comments

Re:Density?

[Spock the Baptist]

"f=ma"

Only if mass is constant.
Newton actually said: F = dp/dt.
Recall that p = m*v, thus
d/dt (m*v) = m * dv/dt + dm/dt * v.

Now if mass is constant, then dm/dt => 0,
& the second term goes to 0 as well; leaving only the first term: m*a,
ergo for constant mass, & only for constant mass does F = m*a.

My two minutes are up...