TL;DW - Biology first, THEN physics.

August 27, 2014 10:38 AM

Why are Stars Star-Shaped? A SLYT of one of the innumerable little educational youtube channels explaining something that always fascinated me.

Educational Youtube channels give me much hope for the next generation. Though they still get all over my grass way too often.

posted by DigDoug (16 comments total)

It's sometimes a source of heated debate when an amateur astronomer with a telescope that doesn't have struts 'artistically' adds this effect in afterwards in software.
posted by edd at 10:53 AM on August 27, 2014

It just occurred to me that this effect could actually be considered useful - the "rainbow" effect might concisely encode spectrum information that gets otherwise lost in the conversion to an RGB image. (And of course the "artistic" postprocessing would not have this property, operating on an RGB source to begin with.)

And now I'm wondering how a digital camera that accurately captured spectrum information would work, and what the file format would be like. Do such things exist? (If they do, they are probably in the hands of astronomers.)
posted by NMcCoy at 11:05 AM on August 27, 2014 [2 favorites]

Oh to have eyesight good enough not to see stars as little fuzzy balls. Sigh.
posted by yoink at 11:07 AM on August 27, 2014 [4 favorites]

NMcCoy: Some kinds of detectors have this ability - notably X-ray proportional counters and probably other kinds not off the top of my head, but optically not really. We use CCDs all the time. What you can do is pipe every pixel position's light down an optical fibre to a spectrometer and then you get an integral field unit. The professional astronomy data format FITS is quite happy with the resulting 'data cube'. (Personally I think it's a format in dire need of an overhaul, but that'd be too much work for us.)

I'm not aware of anyone using accidental diffraction spikes to gain spectrum information either, but slitless spectroscopy is sometimes done when you don't have to worry about disentangling light from neighbouring sources too much.
posted by edd at 11:13 AM on August 27, 2014 [3 favorites]

It just occurred to me that this effect could actually be considered useful - the "rainbow" effect might concisely encode spectrum information that gets otherwise lost in the conversion to an RGB image. (And of course the "artistic" postprocessing would not have this property, operating on an RGB source to begin with.)

And now I'm wondering how a digital camera that accurately captured spectrum information would work, and what the file format would be like. Do such things exist? (If they do, they are probably in the hands of astronomers.)

Pretty sure most amateur equipment has a single R, G and B sensor type, rather than one for each possible frequency. The astronomers do indeed use diffraction intentionally to collect data, similar to the old Netwonian prism. You can take a picture of that with a digital camera and come out okay, as long as you have a ruler or something to demark wavelengths.
posted by pwnguin at 11:17 AM on August 27, 2014 [1 favorite]

Here's a nice video of a data cube from an IFU observation of a galaxy. You can see narrow band emissions in some frames that flash from one side to the other, as the galaxy is rotating and the forward moving and backward moving sides have a different doppler shift that shifts the wavelength across the galaxy.
posted by edd at 11:23 AM on August 27, 2014

Turns out the excellent David Hogg has had the same idea as you, NMcCoy!
posted by edd at 11:31 AM on August 27, 2014

Aren't stars drawn like stars because of the path of Venus through the night sky or something to that effect?
posted by I-baLL at 11:32 AM on August 27, 2014

Oh to have eyesight good enough not to see stars as little fuzzy balls. Sigh.

I vividly remember the first night I looked up after I got spectacles in 6th grade.
posted by DigDoug at 11:56 AM on August 27, 2014 [1 favorite]

I get so irked when ads or whatever have little starbursts photoshopped in on the highlights but they're oriented all catawampus.

GET IT TOGETHER, PEOPLE!
posted by aubilenon at 12:19 PM on August 27, 2014 [1 favorite]

Educational Youtube channels give me much hope for the next generation.

My 10-year-old daughter has recently started closing the door when she's watching videos on the computer, but every time I open it to tell her it's dinner time or whatever she has one of these (or a different channel's) science videos playing. Either she has very fast video-switching technology or she's trying to prevent per parents from stopping her mad scientist research.
posted by mikewebkist at 12:23 PM on August 27, 2014 [3 favorites]

It's a little satisfying to have reality actually come out a bit like one of those "but have you every really looked at your hand? I mean REALLY looked at your hand?!?" discussions from college.

"Now follow me here, Bob. Stars are pointed because the suture lines in your eyeballs refract light to create a pointed pattern. Everybody's suture lines are different, so everyone sees the points on stars a little bit different. Your own personal suture lines are creating the only particular stars you see, and as far as you as know that is the only way they exist, so you really are the most important person in the universe!!!"
posted by Curious Artificer at 12:39 PM on August 27, 2014

They just look like shiny balls to me. On those rare occasions when I'm not in a city and they actually exist. Does that mean my eyes are perfect? Can I get rid of my glasses now?
posted by bleep at 12:45 PM on August 27, 2014

I went to college with Henry Reich and every time I see one of the Minute Physics videos in the wild I feel a tiny bit of pride even though I literally never spoke to him.
posted by dismas at 2:06 PM on August 27, 2014

That was great. I always thought stars twinkled because of the light passing through the Earth's atmosphere. I didn't know about 'suture lines'.
posted by evil_esto at 1:32 AM on August 28, 2014

The twinkling of stars is because of the atmosphere. The light, moving through the air, makes them appear to move around slightly in the sky and also causes them to dim and brighten. This makes them wobble and wink, which we see as twinkling.

This isn't twinkling; it's the appearance of radiating lines coming out from the stars making them look 'spikey' or star-shaped. If you were on the moon, which has no atmosphere, stars would still look like they had radiating lines coming out of them, but they would be completely still, not twinkling at all.
posted by Dreadnought at 5:33 PM on August 28, 2014