Twinkle, twinkle big fat star; how I wonder what you are.

May 31, 2008 8:09 PM

In my view of the sky from Mobile, AL - looking southward - there is a star shimmering brightly in red, yellow and even green. What is it?

I was sitting on the back porch last night when I first noticed it. To begin with I thought it was a plane, until I realized that it wasn't going anywhere. I told my husband about it today - we tried to Google it without luck - and tonight we went out there to see if I knew what I was talking about that is, if it was really" there. True to celestial form, it was right there waiting for someone to look. :)

It's very bright and twinkling like no other star. My husband is fairly good in astronomy, but he's not sure what it is either. Can anyone tell me what it is? Why is it twinkling in so many colors? I've looked at a couple of sites for celestial events but without luck.

posted by magnoliasouth to science & nature (25 comments total)

Sirius?
posted by owhydididoit at 8:26 PM on May 31

It's definitely not Sirius. In fact, that's what my husband told me he thought it was before he looked at it. Once he did though, he realized that I was right. It's not Sirius. It's visible right now if anyone can take a moment to look. It started close to the horizon in the southeast.

As for the reflection, I'm wanting a real and helpful answer thanks.
posted by magnoliasouth at 8:36 PM on May 31

I checked Starry Night, a starchart program and it could possibly be Antares, a red giant. Visual magnitude is -5.31. The color change is most likely because it is a binary star and its partner isn't blocking the light right now. Also, being closer to the horizon, it appears larger and has more dust to filter through.

Planets are also known to change color, but there aren't any in the southern sky right now.
posted by idiotfactory at 8:44 PM on May 31

Yeah, I'm guessing Sirius.

Can you recognize the constellation Orion? If so, follow the line of his belt to the left. Do you (more or less) hit this star, fairly soon, a la this? If so, that's Sirius.

Stars twinkle because the atmosphere is constantly moving around, and the light from the star is refracted, so that different amounts reach you at different points in time.

Stars twinkle in different colors because they're actually giving off all those colors, and the moving atmosphere affects each of those colors in different ways, so different amounts of different colors reach you at different times.
posted by Flunkie at 8:45 PM on May 31

It's definitely not Sirius.

I should have previewed, I guess.

It's visible right now if anyone can take a moment to look. It started close to the horizon in the southeast.

Where is it right now?
posted by Flunkie at 8:49 PM on May 31

Also:
Sirius is currently 32º below the horizon.
May 31st is the best day to view Antares.
posted by idiotfactory at 8:51 PM on May 31

*sigh* I know how to find Sirius (my husband especially) and once again this is not Sirius. The star that I'm seeing is further east than Sirius and it's not much brighter than Polaris.

What other star could it be? Who would know that I could ask? My daughter called her boyfriend a few minutes ago and he took his parents outside. They live in Minnesota and even they could see it. They too agree that it's not Sirius but also like us, are not sure what it is.
posted by magnoliasouth at 8:55 PM on May 31

*sigh* I know how to find Sirius

*sigh* Yeah, um, so sorry.
posted by Flunkie at 9:02 PM on May 31 [3 favorites]

Antares might be it, but isn't that directly over head? This one is rather low over the horizon. Right now, it's visible above the horizon to the southeast. I wish I could explain it better and darn if I don't have a decent camera!

I really appreciate all this help. :)
posted by magnoliasouth at 9:06 PM on May 31

No problem Flunkie. :) I really am thankful for this. It's just the most amazing thing I've ever seen!
posted by magnoliasouth at 9:07 PM on May 31

If nobody here can help, you might try contacting the Mobile Astronomical Society. It looks like there are a couple of observatories in the city, too... GON and Pine Lake (can't find their numbers after a quick Google, though). This page also lists a couple in Alabama. I'm sure if you call them, they'll be able to help you out.
posted by lhall at 9:07 PM on May 31

Here is the starchart for Mobile at 11:14 pm Central time: sky.png 818KB
It could be Jupiter, but planets don't usually flicker. Got binoculars?
I really wish I could see this... damn light pollution.
posted by idiotfactory at 9:19 PM on May 31

Download a copy of Stellarium ("Free, Open Source Planetarium") for your computer. Set your location, time, date, and simulate the sky. Hopefully, your star will be unmasked.
posted by taubman at 9:30 PM on May 31 [1 favorite]

Following my own advice, Looks to me like the likely candidates are Antares, Jupiter, or possibly Spica
posted by taubman at 9:38 PM on May 31

As for the reflection, I'm wanting a real and helpful answer thanks.

I thought mine was. Sorry it didn't work for you. Good luck!
posted by owhydididoit at 9:40 PM on May 31

Thanks to all so far! I'm thinking it's Atares, but not my husband. It's definitely not Jupiter, but I'm going to look into Spica now to see. I've tried looking at idiotfactory's png (which is amazing) but I'm having trouble with my orientation. :(

If anyone can see it outside and knows, I'd love to hear. For now, I guess I'll call some of the places lhall suggested. My curiosity is definitely peaked.
posted by magnoliasouth at 9:49 PM on May 31

In the png image, compass points are shown in yellow characters along the bottom. Jupiter is SSE and low on the horizon, Antares is almost due south and a little higher. Spica is out of view in this png, but Stellarium will show you that its SSW, and higher on the horizon than Jupiter and Antares. You say you're sure its not Jupiter- is that because you're able to identify Jupiter separately, or you're "just sure"?
posted by taubman at 10:18 PM on May 31

Houston, TX here. Going from what you described, I'm guessing either Shaula or something near it.

Stellarium view.
Shaky camera view.

Sorry about the pic, I've got a street light just off the bottom of the frame.

Any of that look like what you're seeing? I was getting twinkle from Shaula and Lesath.
posted by cryosis at 10:24 PM on May 31

It could be Jupiter, but planets don't usually flicker

Atmospheric effects cause flickering on pretty much anything you can see in the sky. Planets sometimes seem to flicker less because they're closer, but you can't depend on that as a classification method.
posted by chrisamiller at 1:29 AM on June 1

"Planets sometimes seem to flicker less because they're closer''
This cannot be right. Both stars and planets are well beyond the atmosphere, and are both near enough at infinity as far as any effects that could be relevant here are concerned.

It might be because planets are often brighter or subtend enough angle not to be pointlike, but it's not because they're closer.
posted by edd at 4:25 AM on June 1

My understanding is that planets don't twinkle (or twinkle less) because they're visually larger. Stars are pinpoints; the atmospheric effect disturbs just that point. With a planet we see a disk. Atmospheric effects from one point on the disk tend to cancel out those from other points on the disk. Correct me, you experts.
posted by booth at 7:53 AM on June 1

It might be because planets are often brighter or subtend enough angle not to be pointlike, but it's not because they're closer.

And planets subtend a larger angle because...
posted by ROU_Xenophobe at 8:19 AM on June 1

ROU_Xenophobe: exactly.
posted by chrisamiller at 9:00 AM on June 1

Magnoliasouth puts the unusual character of this object largely in terms of the way it twinkles in colors:

there is a star shimmering brightly in red, yellow and even green. What is it?...It's very bright and twinkling like no other star. ...Why is it twinkling in so many colors?

I think it's open to question whether the colors she is seeing are a direct consequence of differing wavelengths of light hitting her retina. For one thing, the proportion of the energy in any one spectral color of the light of a star is relatively small, and that would seem to imply that the star during flickers of color due to light broken up into its separate colors by refraction or diffraction should appear to be dimmer than the star when it is seen as white.

But there is another mechanism that could be giving rise to a perception of color here, the differing time constants of the three classes of color sensing cones most people have. Differing time constants means roughly that a given neuron of each of the three classes of cones can add up all the light energy that falls on it over a different (longer or shorter) period of time before reaching the firing threshold. That means white lights flickering at certain frequencies can give rise to a perception of a wide range of colors. That's the basis of the famous illusion in which a white disk with broken up blocks of black on it will seem strongly colored when spun at the right RPMs. (I've always wanted to have a frisbee with that pattern printed on it.) It's also the basis of some attempts made in England to use patterns of flicker to make black and white TV show colors-- attempts that reportedly made unsuspecting viewers think they were losing their minds.

In this case, I suspect some unusual pattern of turbulence of the Earth's atmosphere is causing an unusual pattern of flicker to produce a sensation of color; or in other words, magnoliasouth may not be seeing the frequency spectrum of the light of that star, she may well be 'seeing' the frequency spectrum of the twinkling of the star.
posted by jamjam at 2:26 PM on June 1

ROU_Xenophobe and chrisamiller: the point is that the angular size is the important thing. Angular size is a function of both distance and physical size, and the fact that planets are close enough that it still outweighs their vastly smaller physical size to give them a larger angular size is lucky for you.
If we happened to live close enough to another star for one to have an appreciable disk you'd be flat wrong, and arguments that depend on the luck of where you happen to live tend not to be considered that hot.

Stating that "Planets sometimes seem to flicker less because they're closer'' leads to no greater understanding of what's going on. "Planets sometimes seem to flicker less because they are larger in the sky" would at least start to lead in the direction of understanding the cause.
posted by edd at 3:46 PM on June 1