if (document.images) {
   var image1a = new Image();
   image1a.src =  "../../images/nav_home_off.jpg"; 
   
   var image1b = new Image();
   image1b.src =  "../../images/nav_home_on.jpg";   

   var image2a = new Image();
   image2a.src =  "../../images/nav_science_off.jpg"; 
   
   var image2b = new Image();
   image2b.src =  "../../images/nav_science_on.jpg";   

   var image3a = new Image();
   image3a.src =  "../../images/nav_imageGallery_off.jpg"; 
   
   var image3b = new Image();
   image3b.src =  "../../images/nav_imageGallery_on.jpg";   

   var image4a = new Image();
   image4a.src =  "../../images/nav_news_off.jpg"; 
   
   var image4b = new Image();
   image4b.src =  "../../images/nav_news_on.jpg";   

   var image5a = new Image();
   image5a.src =  "../../images/nav_astronomers_off.jpg"; 
   
   var image5b = new Image();
   image5b.src =  "../../images/nav_astronomers_on.jpg";   

   var image6a = new Image();
   image6a.src =  "../../images/nav_survey_off.jpg"; 
   
   var image6b = new Image();
   image6b.src =  "../../images/nav_survey_on.jpg";   
}
function swap1(state) {
	if (state) {
		document["home"].src = image1a.src;
	} else {
		document["home"].src = image1b.src;
	}
}
function swap2(state) {
	if (state) {
		document["science"].src = image2a.src;
	} else {
		document["science"].src = image2b.src;
	}
}
function swap3(state) {
	if (state) {
		document["imageGallery"].src = image3a.src;
	} else {
		document["imageGallery"].src = image3b.src;
	}
}
function swap4(state) {
	if (state) {
		document["news"].src = image4a.src;
	} else {
		document["news"].src = image4b.src;
	}
}
function swap5(state) {
	if (state) {
		document["astronomers"].src = image5a.src;
	} else {
		document["astronomers"].src = image5b.src;
	}
}
function swap6(state) {
	if (state) {
		document["survey"].src = image6a.src;
	} else {
		document["survey"].src = image6b.src;
	}
}