Talk:Umbra

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[edit] Problem with diagram

The diagram shows the antumbra to be lighter than the penumbra. The text says the antumbra is darker than the penumbra. A contradiction?

[edit] Clean up 2006/05

This article has a whole heap of 'stuff' about the word umbra. Perhaps most of it could be put on an disambiguation page and the core of the article becomes umbra, with reference to shadows, as it once may have been intended? POds 03:58, 5 May 2006 (UTC)

[edit] Disambig?

As mentioned, it has a whole heap of meanings lumped onto one page. I tired seperating them out as best I could. However I feel that the main focus of this page is the use of Umbra in an astronomy/physics sense, as in dealing with light sources. Therefore, I propose a disambiguation page for Umbra, so that the other topics mention can be elaborated on as well. Stovetopcookies 04:41, 5 May 2006 (UTC)

  • I made the disambig page and moved everything there. Since this article is short, and because their definitions depend on one another, perhaps umbra and penumbra should be merged into one article (like deferent and epicycle)? --Fastfission 21:42, 5 May 2006 (UTC)

In law you would use penumbra so it is important to possibly seperate that out as well.

[edit] Sorry.

I am still new to this but I happend upon it when I was trying to point someone in the right direction. It is important because when you discuss law it is a term clarifying that the right is not in the constitution but in the penumbra.

[edit] merge umbra and penumbra

It looks like both these words have lots of uses, but they do also have very specific definitions, as parts of shadows. How about:

  1. the definitions go to Wiki Dictionary
  2. we add a disambiguate page for penumbra (instead of the list of other meanings)
  3. the eclipse and sunspot specific uses of umbra, penumbra, and antumbra go to the articles on eclipses and sunspots

Lisamh 03:39, 20 September 2006 (UTC)

For: I am for the merge. These topics are very short, and besides, the figure illustrating these concepts shows both umbra and penumbra. Lunokhod 20:55, 7 January 2007 (UTC)

[edit] Merged

I've merged not only Penumbra, but also Antumbra, to Umbra. Quarl (talk) 2007-02-28 10:41Z

  • Why not move to, say, Umbra and penumbra? Seems to be more in line with what I've seen on other articles. Cctoide 18:02, 19 April 2007 (UTC)

[edit] question?

Could someone please address the legal use of the word penumbra. i.e. "If you are a history buff you will recall the confirmation hearings of Thomas, Scalia, and Robert Bork.  Specifically, the exchange of views concerning the US Constitution and its “penumbra of rights.”  The “penumbra” area is a dividing line for many constitutional scholars (and politicians)." —Preceding unsigned comment added by 141.197.12.183 (talk) 13:26, 24 September 2007 (UTC)

[edit] Diagram

It'd be really great to extend the diagram to the right (as it is currently oriented). That would allow for the antumbra region to be visible also. Additionally, orienting the diagram vertically, with Earth at the "bottom" might be intuitively easier to imagine.

My two cents on classification issues. The current set-up is probably best.

  • Umbra is the basic idea: the Sun's shadow in a total eclipse.
  • Penumbra is the name for the partial shadow of partial eclipse.
  • Antumbra the name for the special ring effect.

All three ideas belong together as the diagram (if extended) would demonstrate. An article heading Umbra, penumbra and antumbra is just a little unwieldly imo, especially when it is clear these terms are all based on -umbra.

Extention of this article is possible in various ways. One that jumps to mind is that antumbra must happen because the Earth's orbit is elliptical. Hence when Earth is closer to the Sun (perihelion), the apparent size of the sun is larger.

Any recent historical example of an eclipse that cast a shadow over Europe or USA could be really helpful for people to get a feel of how the shadow moves across the surface of the Earth. The cities that fell under the umbra could be named, and the width of the penumbra could be described.

I wish I could provide these things myself, but I have not the skills or access to data. Alastair Haines 03:52, 29 September 2007 (UTC)

It'd be really great to extend the diagram to the right (as it is currently oriented). That would allow for the antumbra region to be visible also.
Done. The new diagram has been computer generated, so the shadow should be "correct".
Qarnos (talk) 07:00, 8 March 2008 (UTC)

[edit] Point source

I just changed the point source reference, as it said that a point source would cast an umbra and penumbra, but no antumbra. I don't see how you can get a partial shadow from a point source - either you can draw a line to it or not, there's no partial shadow. --198.103.172.9 (talk) 17:19, 23 May 2008 (UTC)