Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_android_vs_ios_winners.thumb.jpg.803608cf7eedd5cfb31eedc3e3f357e9.jpg

Recommended Posts

We are running a session at my local society on transits and occultations. One station will focus on exoplanet transits, and we'd like to build a very simple model to demonstrate this. We have a star (light source) and an orbiting "planet" but I need to work out how to detect the changes in light intensity and display this on a laptop, like a classical transit photometry trace below (taken from https://heasarc.gsfc.nasa.gov/docs/tess/primary-science.html).

Is there a way to take a feed from a DSLR through the USB output to do this, else I could get an adapter for my ZWO and put an EOS lens on the front of that. I really do want a light intensity vs time trace in real time on the laptop. This model will be run in a darkened room.

Thanks for any comments.

James

 

transit_white.png

  • Like 1

Share this post


Link to post
Share on other sites

Interesting idea.

Depending on distance and size of light source and occulter, I think that you will benefit from longer focal length lens. Think your best bet is to use ZWO camera for this, and I'm afraid you'll need a bit of custom software to do it.

Easiest way is to do "calibration" of image upon setup - quite easy thing to do - you just need to "mark" circle that represents diameter of light source. After that you take sequence of images and calculate sum of pixel values in marked region, and output real time graph based on this value. Make sure you don't saturate light source, so use fairly short exposure for your subs (this helps with "feed" being real time).

Share this post


Link to post
Share on other sites

Thanks. I was thinking of using a telephoto lens anyway, 70-300. 
 

The other option I thought was to just run canon utilities on the laptop with live view, and then make a suction cup to stick onto the screen with a light dependant resister inside and attach that with some simple circuitary with the help of a friend, to a small oscilloscope...

 

  • Like 1

Share this post


Link to post
Share on other sites
2 minutes ago, jambouk said:

Thanks. I was thinking of using a telephoto lens anyway, 70-300. 
 

The other option I thought was to just run canon utilities on the laptop with live view, and then make a suction cup to stick onto the screen with a light dependant resister inside and attach that with some simple circuitary with the help of a friend, to a small oscilloscope...

 

Well yes, that is also interesting option and I believe it should work as well.

Share this post


Link to post
Share on other sites

We are going to try a light dependent resister in a cardboard tube and point it towards the star, and send the feed to the oscilloscope... 

  • Like 1

Share this post


Link to post
Share on other sites

James there is a very simple piece of software (freeware) called LightGrapher which is made exactly for this purpose - no need to muck about with arduino or anything else.  You can even use it with a simple web cam; here's the link for the download and suggested activities. I've used it in school and it produces excellent transit graphs. Depending on your model set up you can experiment with effect of distance to star, size of planet, transit time etc. For the star I used a globe style lamp and for planets I had a snooker ball,  a computer mouse ball and a polystyrene ball rotating round the globe on a simple turntable.  The planets were placed on an arm which allowed the orbital distance to be varied. If it would be helpful I can photograph the setup but it won't be until Monday. 

http://www.planetarium-activities.org/shows/sp/lightgrapher

Globe Lamp - IKEA

 

Jim 

Edited by saac
  • Like 4

Share this post


Link to post
Share on other sites
2 hours ago, saac said:

For the star I used a globe style lamp

I was just thinking about this, and this is excellent way to do simulation to get proper results. Have not thought about it previously, but this thread gave me food for thought.

I was under impression that star is providing uniform illumination (or rather I always thought of stars in two terms - either single point of light or uniformly lit disc), but above transit graph shows it is not the case. If one wants to properly simulate this and get exact curve - this needs to be taken into account.

I'm talking about this region of graph:

image.png.4a1e6068b3f5a6ddbd384e9d226bcbdd.png

It shows section of the transit where planet is fully "inside" stellar disc. Why should there be dip in this section of the graph? If you observe purely geometrical aspect - you have two surfaces - that of the star and that of the planet - both circles, and "total light emitting" surface is equal to their difference. However this line of reasoning does not include the fact that amount of emitted light from the star depends on angle on its surface!

I'm sure I've seen this effect before, but have not payed attention to it, and here is an example of it:

image.png.d7273861664671017b92748762c91e65.png

If you look at this Ha image of our sun - you can see that it is not uniformly lit (disregard features and look at average brightness of surface). It is brighter at the center than towards the edges. Planet disc near the edges will remove less light than that close to center of the disk - that is why there is "dip" in curve.

You should either use image of the sun on a black background evenly illuminated with some source, or as suggested - globe type lap as it should provide similar effect.

  • Like 2

Share this post


Link to post
Share on other sites

Thanks both. The LightGrapher thing is good; it just took time to work out how to get it to run on my laptop, I can only get it to run with FireFox for the moment and only with the inbuilt camera on the laptop, not another one via USB, but will try again tomorrow.

The limb darkening thing is interesting and I'd not thought about it before, though actually I think I recall someone talking about this at a meeting when exoplanet detection was all the rage. For the simple model I need, I don't think it is necessary to factor this in, but maybe worth mentioning for the more advanced members of the audience.

I also recall from a meeting where an academic was showing transit traces, that the dips in light intensity during a transit were not symmetrical; the onset of the dip had a different morphology to the offset of it. I went up and asked him afterwards and he explained why, but I've totally forgotten what he said...!

James

 

  • Like 1

Share this post


Link to post
Share on other sites
3 minutes ago, jambouk said:

I can only get it to run with FireFox for the moment and only with the inbuilt camera on the laptop, not another one via USB, but will try again tomorrow.

Try installing WDM drivers for USB camera (if it is ZWO camera) - software probably uses WDM type driver to access the camera.

Share this post


Link to post
Share on other sites
32 minutes ago, jambouk said:

Thanks both. The LightGrapher thing is good; it just took time to work out how to get it to run on my laptop, I can only get it to run with FireFox for the moment and only with the inbuilt camera on the laptop, not another one via USB, but will try again tomorrow.

 

James I run it on MS Edge and it woks ok.  I also just use a bog standard web cam so I can have greater freedom to position the camera but the laptop cam works fine as well. You may just need to update some drivers (uses Adobe Flash on MS Edge)

Jim 

Share this post


Link to post
Share on other sites

It is a bit noisy... but was running at 12V when only meant to run at 4.5V; need to find a suitable power source before something burns out...

  • Like 1

Share this post


Link to post
Share on other sites
Just now, jambouk said:

It is a bit noisy... 

...music of the spheres. 

Regards Andrew 

  • Haha 2

Share this post


Link to post
Share on other sites

The LightGrapher software worked a treat and several people asked about it.

A very sucessful evening on transitsand occultations where we all learnt a great deal, and had fun. Amateur indoor astronomy at its best.

James

 

  • Like 2

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

  • Similar Content

    • By alanjgreen
      Just bagged 10 minutes between the clouds and got to see the Mercury shadow transit!
      Its so long since I used the Lunt that I took a few seconds to get back into the groove of tuning the double stack and letting some air into the tuner as it was flat.
      Not much else on the disc - 3 x sets of proms, 3 tiny filaments, saw one small bright flux patch briefly.
      But the Mercury shadow was nice and clear and a decent sized patch too.
      Just got back inside before it started spotting with rain! Fingers crossed for another clear patch later ...
      Alan
    • By ian61
      We are hoping to observe the transit in school (Don’t panic - we have done several transits and partial eclipses in the past so we are fine on the safety aspects - thanks). However does anyone know how I can get hold of some links to use in advance of the day that we can use to put some professional feeds up on the large screen tellies we have linked up to the computer systems these days – I am told that links on YouTube are the easiest to handle on the slightly clunky system we have to control them.
      My question comes from reminiscing with colleges that my daughter and I had stayed up to watch first contact of the last transit of Venus live from Hawaii before swapping to Mt Wilson. (We were also up before dawn on top of the local hill fort as the sun rose having lugged an old 4” reflector up there.) Of course at the time we were just browsing through the internet not taking good note of sites we were on.
    • By LuminousCRO
      I was looking to get into astrophotography with my 10 inch dobson and for start would like to buy something affordable. Cameras can be used or new. Thanks in advance!
    • By Neiman
      Hiya, have absolutely no idea where to begin finding a camera for Astrophotography. And by that I mean - I know I want a canon but am unsure which to buy. It will be a second hand one. Does it need to be full frame ? Can any and all models be modified ? Is a higher pixel count the way to go ? What are the important things to look for in a DSLR ?
      any help would be great.
      Thanks
      Neil
    • By Xiga
      Back in early Feb I tried imaging Markarian's Chain, but after 2 subs I encountered guiding issues (a first for me) so had to give up. 
      So just for kicks and giggles, I decided to process them! ? 
      So this is 2 x 10mins. With the D5300, 80ED and HEQ5-Pro. 'Stacked' (if it's even right to use that term!) in APP, and processed in PS. Then reduced to 75% for posting. 
      Why oh why oh why..... I honestly don't even know myself ?

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.