Something strange is going on with the North Star

Live Science ^ | 03/11/2020 | Rafi Lezter

[BenLurkin]

The problem with Polaris is that no one can agree on how big or distant it is.

Astrophysicists have a few ways to calculate the mass, age and distance of a star like Polaris. One method is a stellar evolution model...Researchers can study the brightness, color and rate of pulsation of the star and use that data to figure out how big and bright it is and what stage of life it's in.

These models are especially precise for cepheids, because their rate of pulsing is directly related to their luminosity, or brightness. That makes it easy to calculate the distance to any of these stars.

But there are other ways to study Polaris, and those methods don't agree with the stellar evolution models.

Researchers [have] seen enough of the companion star in recent years to have a pretty detailed picture of what the orbit looks like. With that information, you can apply Newton's laws of gravity to measure the masses of the two stars... That information, combined with new Hubble Space Telescope "parallax" measurements — another way to calculate the distance to the star — lead to very precise numbers on Polaris's mass and distance. Those measurements say it's about 3.45 times the mass of the sun, give or take 0.75 solar masses.

That's way less than the mass you get from stellar evolution models, which suggest a value of about seven times the mass of the sun.

This star system is weird in other ways. Calculations of the age of Polaris B suggest that the star is much older than its bigger sibling, which is unusual for a binary system. Typically, the two stars are about the same age.

[GingisK]

I just couldn’t conceive of great big globs of flotsam floating about between here and there, could you?

[schurmann]

“As long as we can see it and it guides our sailors... We’ll be fine.” [jerod, post 4]

Polaris seems unmoving only to the unaided eye.

It actually “moves” in a small circle about the zenith of our planet’s north pole: a radius of about one degree, if my memory is accurate. Small as this sounds to an average citizen, failing to correct for it can induce significant errors in celestial navigation.

Timing and measuring must be very precise, to obtain usable information from celestial observations: a timing error of 15 seconds causes a position error of a nautical mile; an error in observing a star’s altitude of one minute of arc (one 60th of one degree of arc) can throw off the calculated position by up to one nautical mile.

The federal government used to publish tables that would permit users to correct for time of day and approximate location on the surface of the Earth. Not sure if it’s still being done; GPS and INS have changed the situation a great deal - for seafarers, aviators, and other users.

[Sequoyah101]

It could be that they don’t know as much as they think they do.

How could that be possible?

[SunkenCiv]

Thanks BenLurkin.

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[Redcitizen]

Chang: I am constant as the Northern Star...
Leonard McCoy: [to Spock] I’d give real money if he’d [Chang] shut up.

[SunkenCiv]

A Case of You - Joni Mitchell