Starship Asterisk*

I was showing my son the APOD site a few days ago and he noticed something that was somewhat peculiar – peculiar enough that I thought I ought to ask about it. On http://apod.nasa.gov/apod/ap080318.html near the bottom of the photo there is a star that is ovoid in shape.

(It is more noticeable at actual size – located near the bottom of the photo, under the right nebula, and roughly 10:00 from the bright star with the 4 rays)

He asked me why that star was an oval when all the others were round, and the only answer I could come up with was that maybe it was moving when the picture was taken – but that doesn’t make much sense, really.

Do you have any idea why that particular star would be oval in shape? It sure seems odd.

nuance wrote:...On http://apod.nasa.gov/apod/ap080318.html near the bottom of the photo there is a star that is ovoid in shape.

(It is more noticeable at actual size – located near the bottom of the photo, under the right nebula, and roughly 10:00 from the bright star with the 4 rays)...

Do you have any idea why that particular star would be oval in shape? It sure seems odd.

It's probably not just one star. Possibly a binary or a chance alignment of unrelated stars.

Does look alittle oval-ish don't it...


There are no others in the image that are that aligned if thats the case.





Altair is an oval shaped sun...
http://news.bbc.co.uk/2/hi/science/nature/6709345.stm

These are both good answers - certainly better than "maybe it's moving?"

From that article you linked on Altair - they needed an array of telescopes to see enough detail to determine (or prove) that the star was oval. From this APOD, it looks like a single back yard telescope took this picture.

If, as stated in that article, all we see are "points of light" when we try and image stars, how can we see such a clearly defined oval / ovoid shape on this star?

I looked at every picture I could find on the net of M78 and didn't see this particular star in any of them (though that's not a scientific or definitive statement by any means!)

Arramon wrote:There are no others in the image that are that aligned if thats the case.

There appears to be a bit of an image overlap (artifact?) Maybe one star hiding behind another. Or my imagination.

We cannot resolve stars into disks (well, just a few really close, big ones, but not with amateur equipment and not at this relatively low focal length). No matter how oblong a star may actually be you wouldn't see it as ovoid in an image like this.

The disks you see in images such as this one are from the relatively bright point light sources (stars) essentially overwhelming the imaging equipment, due to the light diffracting around the edges of the optics and also to some extent spilling over to adjacent photosites on the imager itself.

What you're seeing is really two stars of similar apparent brightness that appear very close together (though they may be a huge distance apart in actuality). Note the following image from the Digitized Sky Survey, with 1 arc-second per pixel resolution. You can better see it's a close double here.



Oh, and stars DO move - it's called "proper motion", but you wouldn't detect it in an exposure this short. You can actually see the proper motion of many stars due to their changed positions when carefully comparing exposures taken many years apart.

-Noel

nuance wrote:I looked at every picture I could find on the net of M78 and didn't see this particular star in any of them (though that's not a scientific or definitive statement by any means!)

The orientation of http://antwrp.gsfc.nasa.gov/apod/ap030121.html is about the same, and your star shows in the same position.

http://antwrp.gsfc.nasa.gov/apod/ap061010.html is rotated 90 clockwise. M78 is at the bottom. Your star is at about 8:30 to M78.

Oh well, it's not technically "my" star! heh.. thanks everyone for the help, I have enough info now to explain this to my 7 year old son, and preserve his opinion that I am the greatest, most smartest Dad in the world.