I Do stars in the ecliptic seasonally change brightness?

[KurtLudwig]

TL;DR Summary

Is Regulus brighter in February? Alpha Leo lies close to the ecliptic plane, b=+0.46 deg, mag. 1.36. It is eclipsed by the Sun on about Aug. 23.

Has any astronomer observed any seasonal changes in the brightness of stars lying close to the ecliptic plane? (Other stars are: d Cnc b=+0.08, mag.=+3.9; d Gem b=-0.18, mag.=+3.5; a Lib b=+0.33, mag.=+2.7.) Once a year these stars are occulted by the Sun. What happens from the date of occultation to the brightness at 3 months, 6 months and 9 months from that date?
Are there any sites where I can search for data?

 

[Keith_McClary]

There would be a very tiny relativistic effect, since Earth's orbital velocity relative to a star changes seasonally.

 

[hutchphd]

Do you have a hypothetical reason to expect such variation?

 

[Bandersnatch]

There would be a very tiny relativistic effect, since Earth's orbital velocity relative to a star changes seasonally.

You're thinking of relativistic beaming? Like all relativistic effects, it's negligible for non-relativistic speeds. You'd need waaaaay more significant numbers on your magnitudes to start registering any effect.

 

[Vanadium 50]

You'd need waaaaay more significant numbers on your magnitudes to start registering any effect.

And stars that are waaaaaay more stable than physical stars. Like a million times more stable than the sun. And no starspots.

 

[Keith_McClary]

And stars that are waaaaaay more stable than physical stars. Like a million times more stable than the sun.

We could average over billions of stars. 🖥

 

[snorkack]

And stars that are waaaaaay more stable than physical stars. Like a million times more stable than the sun. And no starspots.

No
Aberration is a well known phenomenon, discovered two centuries before relativity and a century before parallax.
Obviously, Earth orbital motion also changes Doppler shift... also discovered half a century before relativity.
My estimate is that redshift and blueshift due to Earth orbit should change star magnitude by 0,02 %. For comparison, magnitude of Sun changes by 0,1 % between quiet and active. And less in short term.
If your star is stable enough and telescope precise enough to measure change of magnitude due to Earth sized planet transiting - which is common - then you should also see magnitude changes due to Earth orbital blueshift and redshift.

 

[chemisttree]

If you are interested in variable stars, here is a free resource. 373 pages!
You might be interested in joining AAVSO as well. Their website is a wealth of information about variable stars.

If the Earth were embedded in a dust cloud that was not isotropic with respect to Earth, you might expect starlight to be more or less absorbed depending on the relative position of the star with respect to Earth. In fact, Earth IS embedded in such a cloud of interplanetary dust. It gives rise to what is called the zodiacal light but I’m not sure if the zodiacal dust cloud (Interplanetary Dust Cloud or IPD) is substantial enough to change the apparent magnitude of stars in the ecliptic. I think it’s a good question, though.

Didn’t you ask this same question last August?
https://www.physicsforums.com/threa...brightness-change-throughout-the-year.992542/

 

[Vanadium 50]

No

Yes.

The pure photometric increase (i.e. not counting the fact that light is bluer) goes as γ³, or \sim 1 + \frac{3}{2}\beta^2. The Earth is traveling around the sun at β=10^-4 so we are looking for effects of order 10^-8.

 

[snorkack]

Yes.

The pure photometric increase )(i.e. not counting the fact that light is bluer) goes as γ³, or \sim 1 + \frac{3}{2}\beta^2.

Ah. You mean total photon count per unit of time on Earth clock? Nice to know.
But since the standard definition of bolometric luminosity is total energy per unit of time on Earth clock, it does count in the blueshift. Which means that the effect is still in the order of 10^-4.

And visual luminosity counts energy in a specific range. Which means that the luminosity of red stars increases much more than that of blue stars. (Do blue stars actually dim on blueshift?)

 

[KurtLudwig]

Do you have a hypothetical reason to expect such variation?The hypothetical reason is that light very slightly bends around the gravitational field of our Sun. When viewing Regulus on that date, the light coming from it will bend all around the Sun. Will that have a magnifying effect?
Twice a year, the Earth crosses a line between the centers of our Sun and of a star lying very close to the ecliptic plane. Once the star is occulted and the other time, weather permitting, the star can be seen clearly. (The question only applies to stars lying close to the ecliptic plane.) Regulus is one of these stars. For Regulus that date is around February 23. Has anyone noticed any change in brightness? I am giving Regulus as an example since it is has been viewed innumerable times by many astronomers and star gazers. (I have viewed Regulus with binoculars and with a very basic Tasco reflecting telescope.)
Looking at Regulus around February 23, is it noticeably brighter, or, as already has been answered, only by a negligible factor of 0.000001?
Thank you for your answers.

 

[chemisttree]

Gravitational effects might alter the position of a star slightly but not it’s brightness. This has been measured for stars whose light passes very close to the Sun. Obviously only observable during an eclipse.

 

[hutchphd]

Will that have a magnifying effect?

With my (not impressive) knowledge of the subject I think it unlikely. Very roughly:

The deflection of starlight at impact parameter b is $\alpha=2\frac{R_{Schwarzschild}} b$for a point mass

For the sun and a star at the limb this is ~$10^{-6} rad$ so the Earth is well inside any possible focus

Notice also this is not a focusing lens ( the deflection decreases with impact parameter).
So one is viewing off axis a slightly aberrated star.
(Please rescue me if I have said something truly wrong here!).

 

[KurtLudwig]

Thank you for all your answers now and for a similar question during August 2020. I trust your informed answers and your knowledge of astronomy and physics.