Jump to content

Sketches

Unknown object


jonboy51

Recommended Posts

 

 

Does anyone have any idea what this is, it was taken in West Virginia by a friend of mine using a standard DSLR camera on a tripod, it appears every night just after sunset and disappears over the horizon about 2 hours later. Unfortunately he doesn't know which direction he's looking in. When he first told me about it I was convinced it was the Planet Venus, since he described it as a very bright star in the sky appearing just after sunset, but now he's sent some pics, I'm not so sure.

16832854_1234488699920179_171349619_o.jpg

Link to comment
Share on other sites

23 minutes ago, jonboy51 said:

 I was convinced it was the Planet Venus, since he described it as a very bright star in the sky appearing just after sunset, but now he's sent some pics, I'm not so sure.

Yes, you were right ! As others have said = Venus

The odd shape is caused by the shape of the iris in his lens, 5 blades, which is a bit of a surprise to me. I dont have experience of Canon/other DSLRs, but I would have expected 9 blades. Was he using a standard lens ?

edit, ooops crossed in the post with K of CS :)

 

Edited by SilverAstro
Link to comment
Share on other sites

18 minutes ago, jonboy51 said:

 just after sunset and disappears over the horizon about 2 hours later. Unfortunately he doesn't know which direction he's looking in.

Oh, PS  :-  the sun always sets in the west in W.Virginia :) , also any object following the sun soon after will also set in the west. Sometimes a little south of west and sometimes a little north of west depending on time of year.

  • Like 1
Link to comment
Share on other sites

25 minutes ago, SilverAstro said:

The odd shape is caused by the shape of the iris in his lens, 5 blades, which is a bit of a surprise to me. I dont have experience of Canon/other DSLRs, but I would have expected 9 blades. Was he using a standard lens ?

Some of the Canon kit lenses have 5 aperture blades, as does the 50mm f1.8. Confusingly, the latter gives 10 diffraction spikes on bright stars, I don't understand why.

Link to comment
Share on other sites

17 minutes ago, Knight of Clear Skies said:

Some of the Canon kit lenses have 5 aperture blades, as does the 50mm f1.8. Confusingly, the latter gives 10 diffraction spikes on bright stars, I don't understand why.

Diffraction spikes are usually double. The 4 you see from a 4 vane secondary are actually 8 spikes but in overlapping pairs.

On the object - Venus !

  • Like 1
Link to comment
Share on other sites

26 minutes ago, Knight of Clear Skies said:

Some of the Canon kit lenses have 5 aperture blades, as does the 50mm f1.8. Confusingly, the latter gives 10 diffraction spikes on bright stars, I don't understand why.

Oh, now I am really surprised ! I thort 5 straight blades went out with brass portrait lenses, plates and darkened hoods  ! just shows whaduiknow :)

I have not the math of diffraction to hand but I would expect  ( ah John is a quicker typer than me ! ) that 1 vane will produce two spikes ,, actually 1 continuous spike extending across the object. So yes 5 vane edges = 10 spikes.  If venus had been in focus we should see 10 spikes with a tighter less fuzzy 'blob'.  All not helped by Venus being unresolved at this aperture.

edit ooops, everyone is typing faster than me !

Edited by SilverAstro
Link to comment
Share on other sites

16 hours ago, SilverAstro said:

Oh, now I am really surprised ! I thort 5 straight blades went out with brass portrait lenses, plates and darkened hoods  ! just shows whaduiknow :)

I have not the math of diffraction to hand but I would expect  ( ah John is a quicker typer than me ! ) that 1 vane will produce two spikes ,, actually 1 continuous spike extending across the object. So yes 5 vane edges = 10 spikes.  If venus had been in focus we should see 10 spikes with a tighter less fuzzy 'blob'.  All not helped by Venus being unresolved at this aperture.

edit ooops, everyone is typing faster than me !

Correct, even blades give the same number of spikes and odd blades double up as they don't cancel out.

Link to comment
Share on other sites

13 hours ago, jonboy51 said:

Thank you guys for re-assuring me, my friend is not a stargazer, so it's a little difficult to get him to be a bit more definitive in his description, but many thanks to everyone who replied.

Glad we could help. Venus is particularly spectacular and prominent at the moment, so no doubt plenty of people are wondering what it is.

Edited by Knight of Clear Skies
Link to comment
Share on other sites

7 hours ago, wxsatuser said:

 as they don't cancel out.

 Or double up.  I have been thinking that in an even ( 4 vane ) spider it just has two legs that are longer than a 2 vane (triangular) support, but a different situation arises in the case of an even number of blades in an iris.

 

 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.