Nebulae and Galaxies. I don't understand.

Jimmy · #1 08-02-2005, 03:51 PM

Hello all........

Just wondering, the other day (sunday night, what a damn clear night in melbourne!) I decided to get the scope out.

I was looking at orions nebula and the horsehead nebula. I could see them quite well, but was wondering why there was no colour like the pictures I have seen (red etc).

Is it because I wasn't using any filters? Can someone explain to me what filters (colours etc) are the good for looking a nebulae, stars, clusters and galaxies? Also what planetary filters are good for mars, saturn, venus etc?

Thankyou

ballaratdragons (Ken) · #2 08-02-2005, 04:18 PM

That is a very technical question.

Our eyes receive light at a certain speed (like a camera shutter) but our eyes are not fast enough to see the colour of deep space light unless you go very big aperture.

It's not as simple as I have made it sound but that is it in a simple way.

To understand the use of filters go to the '2" Filters' thread in this section and see the web link.

Jimmy · #3 08-02-2005, 04:35 PM

Could I still say... get a false sort of RED COLOUR effect if I used a red filter on the horsehead nebula?

I think I might get a broadband filter.

Thanks for the great webpage advice.

[1ponders] (Paul) · #4 08-02-2005, 04:39 PM

It takes quite a bit more light energy entering our eyes for our colour receptors to respond and see colour, than for our black and white ones to respond. Plus we have many more black and white receptors than colour. (they are called rods and cones, but I can never remember which is which).

Even in really big telescopes (and I mean BIG) the colour from even very bright neb is never like what we see in photos.

I've often wondered why someone hasn't taken telescope manufacturers to the cleaners over the blattant false advertising on the outside of their boxes. You will never see images of nebula and galaxies with the nacked eye as they are portrayed there.

ving (David) · #5 08-02-2005, 04:39 PM

you saw the horsehead? brilliant!
must have been really dark at your site!

Benn chasing that dark neb for a while, buggered if i can see it.

Jimmy · #6 08-02-2005, 04:43 PM

no! I saw it from my melbourne light polluted frontyard/balcony area! It was fantastic! I was very excited... and kept shuffling between saturn, orions neb, and the horsehead! It was a great night. But anyway.... Im trying to find an LPR, I think that may help allot with inner city observing.

ving (David) · #7 08-02-2005, 04:49 PM

what EP did you use? got any tips for me to find it?

Jimmy · #8 08-02-2005, 04:59 PM

I used a meade series 4000 super plossl 26mm and 9mm ep's. It's slightly to the left of orion. Try using the free star chart program to help you locate it much easier at your particular time and location. If you have a goto scope or a small scope with goto use that and point it at that direction with a wide fov eyepiece (you have to know your sky ... I dont't know too much, but I enjoy orion as it is out allot around this time of year and am fascinated by it!!! so i have studied it quite allot). Read some books, and find out the brightest stars near the location (I think it lies southeast of Alnitak, the brightest star in Orion's belt).

Good luck and happy hunting! Try an LPR... Im going to get one and try to suck more detail... also try and use averted vision.

IT HELPS!!!

Starkler (Geoff) · #9 08-02-2005, 05:08 PM

What Paul said about the human eye is correct. It takes a lot more light to see colour than it does to just detect light.

I have never seen colour in any nebulous DSO except for planetary nebulae, which are usually blue/green, whereas others say they see colour in M42 in an 8 inch scope.

Dave47tuc (David) · #10 08-02-2005, 07:00 PM

Jimmy,
You could see the Horsehead???????

This is a very difficult object to observe

I have only ever seen it once in a 22 inch

You may have been looking at ngc 2024, just North of Alnitak.Also called the flame Nebula.

This could be an easy mistake to make!

Sunday night was a very good night, I got out myself and had a ball.

Had a very mates over and we all had a good night.

Glad you had a good night to Jimmy

By the way if you want colour in Nebula with your eye get a big scope say over 18" better a 25"

rumples riot · #11 08-02-2005, 10:08 PM

I have to agree with Dave. I have nver been able to see the Horse head with my scope. Had perfect goto's all that night, so when I went to look, it was not there.

Jimmy · #12 09-02-2005, 12:28 AM

what filters should i buy?

Jimmy · #13 09-02-2005, 12:57 AM

no... im 100% sure it was the horsehead. It was exactly like a side on knight chesspiece facing right.

Im sure... the back part was hard to make out, but the head and front very easy.

actually, it was the flame nebula....... just worked it out by studying pictures how i mixed them up... oh well.. thought I had it made!!!!!!!

iceman (Mike) · #14 09-02-2005, 06:13 AM

heh easy mistake.. from what i've heard, the horsehead is notoriously difficult to observe visually, requiring very dark skies, large aperture, and is helped marginally by a UHC/OIII filter.

Jimmy · #15 09-02-2005, 08:34 AM

ok....so if i used a red filter on a nebula, it would only let red light through, so it would look red anyway to me right?

thats good enough!!!!!!!!!

ving (David) · #16 09-02-2005, 10:09 AM

dunno, sounds... sound. i have a broadband filter which makes m42 look 3d! but i dont have any colour ones :/

rmcpb (Rob) · #17 09-02-2005, 11:19 AM

Yep, its the rods and cones that let you see. They are the cells in your eye that detect light. The cones detect colour and are concentrated around the centre of the back of the eye. The rods detect lower light levels but produce a B&W image and are spread all over the back of the eye.

If you have a huge scope that concentrates heaps of light onto the centre of the back of your eye then it is possible that you will start seeing the colours in the nebulae BUT not many of us have access to these beasts.

This also explains why averted vision works. When you look directly at a nebula the image is focused on the centre of the back of the eye which is composed mainly of cones which are less sensitive to low levels of light so it is more difficult to see the image. By averting your vision a bit you project the image onto the area of your eye that is composed maily of rods which are more sensitive to low levels of light so you can see the image but it is in B&W.

Putting a red filter on an eyepiece to see the nebula in red would be counter productive. The light levels are already low (that is why you can't see the colour already) and the filter would just lower the light levels further by restricting the wvelenghts of the spectrum allowed through. Just enjoy them as B&W with occasional glimpses of colour in some of the brightest ones or when you scrounge a look through a large scope at a star party.

Cheers

ving (David) · #18 09-02-2005, 11:28 AM

plenty of green in m42 if you want colour

astro_south (Andrew) · #19 09-02-2005, 12:55 PM

I was out at Leyburn (Southern Astronomical Society dark sky site) last Friday and Saturday night and I noticed colour in Orion. The "wings" were a green colour and the dimmer areas in the nebula coming down from the wing structure was a distinctive pink to red (in a 12.5" dob). I also spotted the Horsehead nebula as a dark region / bite out of the background nebula. No Horsehead structure was visible - just a dark patch (often described as a thumb shape). This was unfiltered in the 12.5.

cheers

RAJAH235 · #20 09-02-2005, 10:25 PM

Hi Guys, We W.A.A.C.ers are what I like to call *privileged*, in that one of our members has a 17 1/2 " truss tube Dob. The views we get are breathtaking.(He's lucky if he gets to look thru it some nights as we usually take it over). M42, to my eyes, glows fluro green, with just a touch of pink. (weather permitting of course).
Jimmy, what Rob has said is right. The main reason that you can't see colour, is because your eyes/brain process the info. instantly.(not like film which accumulates the light). savvy? Unless, as has been said, you have a BIG t'scope.
(cones = colour----rods = movement/B&W).
As for the Horse head, well it's definitely there, if you use *averted imagination*.
The filters for Planetary Nebula/DSO etc, start with a Broadband, for light polluted areas, a UHC and then an OIII. These give you an ever decreasing range of filtering light,right down to an 11 nanometer range with the OIII.
Best advice is BORROW the one's you're interested in if possible.
HTH,