# Large satellite dish, focus heat? **URL:** \ **Category:** Factual Questions\ **Created:** [April 8, 2004, 8:08pm UTC](https://boards.straightdope.com/t/large-satellite-dish-focus-heat/239019 "2004-04-08T20:08:37Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![MaryEFoo](https://avatars.discourse-cdn.com/v4/letter/m/ba8739/32.png) [@MaryEFoo](https://boards.straightdope.com/u/MaryEFoo)\ **Post date:** [April 8, 2004, 8:08pm UTC](https://boards.straightdope.com/t/large-satellite-dish-focus-heat/239019/1 "2004-04-08T20:08:37Z")
The thread on satellite dishes got me wondering. A dish antenna is a big parabolic reflector with one focus nice and close, and the other one at about infinity. If you lined it with mirror, it could focus sunlight at one very hot spot. Would aluminum foil make a nice cheap mirror effect? How hot would the spot get? Could I melt rocks, smelt ore for metals, use it as a deathray, explode pinecones, sterilize the dishes, kill ants? ---
**Author:** ![Padeye](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@Padeye](https://boards.straightdope.com/u/Padeye)\ **Post date:** [April 8, 2004, 8:15pm UTC](https://boards.straightdope.com/t/large-satellite-dish-focus-heat/239019/2 "2004-04-08T20:15:14Z")
Yes. Something similar is the basis for some kinds of solar cookers. A big C band dish would make a lot of heat as I’ve seen solar oven projects that had less then six square feet area. You won’t be smelting metal but will damn sure be able to incinerate a hot dog. Hmm, my folks have a derelict C band dish… A big pack of Reynolds Wrap from Costco, BWAHAHAHAHA!!! I’m Professor Chaos! Bow down before me! ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 8, 2004, 10:21pm UTC](https://boards.straightdope.com/t/large-satellite-dish-focus-heat/239019/3 "2004-04-08T22:21:37Z")
Yes, it certainly is possible; there was an incident a couple of years back where a children’s playground contained a novelty dished mirror (I’m not really sure why anyone thought this was a great idea) and a child’s hair or clothing caught fire as he played near it in bright sunlight. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 8, 2004, 10:27pm UTC](https://boards.straightdope.com/t/large-satellite-dish-focus-heat/239019/4 "2004-04-08T22:27:01Z")
There’s another way to do this, if you don’t have access to a dish; get a 4x4 sheet of MDF or hardboard and cover it with little square mirror tiles; it is possible to attach them with a single blob of silicone on one corner (nearest to the centre of the board and drive two screws through the back of the board and attach them to the back of the mirror with more silicone blobs (forming a triangle of blobs on the back of the mirror) - each mirror can then be adjusted by the screws so that it reflects light on the same target - a sort of fresnel parabolic mirror. (Although there’s a lot of work involved). ---
**Author:** ![vetbridge](https://avatars.discourse-cdn.com/v4/letter/v/b5e925/32.png) [@vetbridge](https://boards.straightdope.com/u/vetbridge)\ **Post date:** [April 9, 2004, 1:49pm UTC](https://boards.straightdope.com/t/large-satellite-dish-focus-heat/239019/5 "2004-04-09T13:49:40Z")
> [@Mangetout](#): > > There’s another way to do this, if you don’t have access to a dish; get a 4x4 sheet of MDF or hardboard … Like this? [http://www.cockeyed.com/incredible/parabola/parabola.html](http://www.cockeyed.com/incredible/parabola/parabola.html) ---
**Author:** ![MaryEFoo](https://avatars.discourse-cdn.com/v4/letter/m/ba8739/32.png) [@MaryEFoo](https://boards.straightdope.com/u/MaryEFoo)\ **Post date:** [April 9, 2004, 5:07pm UTC](https://boards.straightdope.com/t/large-satellite-dish-focus-heat/239019/6 "2004-04-09T17:07:17Z")
Oh good, that site gives the energy: 127 watts per square foot. So if you have a satellite dish 6’ across, pi-are-squared makes it 3.14_9_127 or 3589 watts per square foot at the hot focus, and 8’ across, it’s 3.14_16_127 or 6380 watts. Bodacious hot.