Photo of the sun through a #10 welding filter

**Krupski** · 07-25-2017, 01:00 PM

In preparation for the upcoming eclipse, I've been experimenting with directly photographing the sun through a welding filter rather than using the "pinhole" trick or using a telescope to project an image of the sun.

This one turned out fairly well... and amazingly there are almost no sunspots visible. I wondered if the filter caused the sunspots not to be seen or if there really weren't any, so I checked the Helioseismic and Magnetic Imager website and sure enough our images look almost identical. There's one tiny bright spot near the left edge of the sun and both the HMI site images and my image see it. I got some blur though... EVERY time I'm ready to fire the shutter the wind picks up and shakes the telescope!

(click pic for larger)

**alismith** · 07-25-2017, 01:08 PM

Did you photograph the right sun? Ours is yellow.

Actually, green stars are the rarest of all the colors....Their temperature ranges are so narrow that most stars pass right through that stage relatively quick.

**El Jefe** · 07-25-2017, 01:16 PM

Cool.

Also, Walmart is selling glasses for safe viewing of the eclipse. They look similar to 3-D glasses used at movie theaters.

**LAGC** · 07-25-2017, 01:55 PM

Originally Posted by El Jefe

Cool.

Also, Walmart is selling glasses for safe viewing of the eclipse. They look similar to 3-D glasses used at movie theaters.

Yep, Amazon has them too:

https://www.amazon.com/Soluna-Solar-...CZL/ref=sr_1_5

But now they're charging $17 for a 10-pack. It was only $10 a month ago.

**Krupski** · 07-25-2017, 04:47 PM

Originally Posted by alismith

Did you photograph the right sun? Ours is yellow.

Actually, green stars are the rarest of all the colors....Their temperature ranges are so narrow that most stars pass right through that stage relatively quick.

Technically, our sun is white... it's color is our definition of white.

Compared to other stars though, it is only yellow. Some stars are so hot that their visible light emission is in the blue range while others are so cool that they appear orange or red.

There is no such thing as a "green" star though. There are illusions caused by stars of two different colors being (visibly to us) very close together, and their combined colors mimic green... a lot like blue and yellow paint mixed together.

Example:

Viewing star color involves the additive primary color spectrum (red, green and blue) instead of the subtractive primary spectrum (magenta, cyan and yellow). This is the same as a computer monitor or TV set.

To make colors other than red, green or blue, two of these are mixed together. For example, red plus green = yellow. Red plus blue = magenta and green plus blue = cyan.

So, as a black body radiator increases in temperature, it's apparent color will change from dull red to bright red, then to yellow (as a result of combining green and red), then finally blue, violet and ultraviolet.

Although there IS green emission, because it's mixed with either red or blue, we can never see PURE green from a black body radiator (although it IS in there... as proven by the fact that using a prism to split "white" sunlight yields the full visible color spectrum, including pure green.

**Krupski** · 07-25-2017, 04:52 PM

Originally Posted by LAGC

Yep, Amazon has them too:

https://www.amazon.com/Soluna-Solar-...CZL/ref=sr_1_5

But now they're charging $17 for a 10-pack. It was only $10 a month ago.

I think I would rather trust a welding filter. Those Amazon cheap-o glasses may be dark, but do they stop infrared radiation?

If not, you could fry your eyes even though the sun looks "dark enough".

In fact, when you process (develop) infrared camera film, you have to do it in a metal tank.

A black plastic developing tank, which is fine for B&W as well as color film, will fog infrared film by letting in ambient IR radiation.

I know a welding filter will stop IR as well as bright visible light and UV as well. I'm not going to risk my eyes to save a few $$$.

**Krupski** · 07-25-2017, 05:01 PM

Want to try something cool? Get a bright red and bright blue LED and wire them up to a battery with the proper resistor.

Tape the two LED's together or whatever so that they both shine in the same direction.

Now, in the dark make a shadow on the wall of your hand with the red/blue LED pair.

You will see two shadows of your hand... one red and one blue, slightly misregistered (i.e. not right on top of each other - like a 3D anaglyph image).

NOW, view your hand shadow while wearing red/blue 3D glasses. The shadow of your hand will appear to be either in front of the wall or behind it (depending on which way the LED's are oriented).

By moving your hand closer to or further away from the LED's (or by moving the LED's closer or further), you can make your hand shadow appear to move away from or deeper into the wall (again depending on which way the LED's are pointing).

By the way, the two LED's need to be held so that one is left and one is right (not one above and one below).

That is, this is right:
* *

This is wrong:
*
*

Have fun!

**l921428x** · 07-25-2017, 05:39 PM

We basically have had no sunspots for months.

Today's offering: http://www.suspicious0bservers.org/ There will be another at 4 or so MT
tomorrow.

**alismith** · 07-25-2017, 06:43 PM

Originally Posted by Krupski

Technically, our sun is white... it's color is our definition of white.

Compared to other stars though, it is only yellow. Some stars are so hot that their visible light emission is in the blue range while others are so cool that they appear orange or red.

There is no such thing as a "green" star though. There are illusions caused by stars of two different colors being (visibly to us) very close together, and their combined colors mimic green... a lot like blue and yellow paint mixed together.

Example:

Viewing star color involves the additive primary color spectrum (red, green and blue) instead of the subtractive primary spectrum (magenta, cyan and yellow). This is the same as a computer monitor or TV set.

To make colors other than red, green or blue, two of these are mixed together. For example, red plus green = yellow. Red plus blue = magenta and green plus blue = cyan.

So, as a black body radiator increases in temperature, it's apparent color will change from dull red to bright red, then to yellow (as a result of combining green and red), then finally blue, violet and ultraviolet.

Although there IS green emission, because it's mixed with either red or blue, we can never see PURE green from a black body radiator (although it IS in there... as proven by the fact that using a prism to split "white" sunlight yields the full visible color spectrum, including pure green.

You are correct. I looked it up and found there is no such thing as a real, green star. It is an illusion, as you say.

I stand corrected.

**Krupski** · 07-26-2017, 05:41 PM

I was messing around with my photo editor program and made this (a simulation of how Betelgeuse will go supernova):

**Helen Keller** · 07-26-2017, 06:00 PM

**JTHunter** · 07-27-2017, 01:40 PM

Krupski - is a #10 glass darker than a #14? What I've been hearing is we should use a #14 welder's glass.

**l921428x** · 07-27-2017, 06:24 PM

No a 10 is lighter the numbers go up.

**Krupski** · 07-27-2017, 06:40 PM

Originally Posted by JTHunter

Krupski - is a #10 glass darker than a #14? What I've been hearing is we should use a #14 welder's glass.

A #10 is lighter than a #14... higher number = darker glass.

I already took a quick glance at the sun through the #10 and it's too bright (or not dark enough

).

I might get a #14 or maybe put two #10's together. The #10 works fine, though, for telescope and camera use (that is, camera attached to telescope, NOT eyeball to telescope).