<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=us-ascii"><meta name=Generator content="Microsoft Word 15 (filtered medium)"><!--[if !mso]><style>v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
</style><![endif]--><style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
font-size:11.0pt;
font-family:"Calibri",sans-serif;}
span.EmailStyle17
{mso-style-type:personal-compose;
font-family:"Calibri",sans-serif;
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri",sans-serif;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]--></head><body lang=EN-US link="#0563C1" vlink="#954F72" style='word-wrap:break-word'><div class=WordSection1><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Study this photo and tell me what you see please.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><img width=728 height=658 style='width:7.5833in;height:6.8541in' id="Picture_x0020_1" src="cid:image002.jpg@01D71D59.B3FDF9A0"><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The explanation is wicked cool.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>This was taken on a camping trip last weekend at a National Park and is a 30 second duration.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>OK everyone saw Orion up there on top right quadrant of the photo.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Our eyes are drawn to the cosmos, but consider the visual clutter at the bottom of the photo, which I needed to explain to my scouts why the stars in the photo appeared streaky, all of them. The structure is a public restroom but it doesn’t have windows. So that vertical light artifact on the left end of the streak is caused by reflected light from a door opening and closing with a light on inside the restroom.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The roof of a foreground car eclipses part of the undulating light path, which is caused by a dual LED headlamp worn by a walking person. The orange glow on the building is stray light perhaps from the headlamp. There is another feature on the right end of the undulating streak which I think is stray light reflecting off of a person entering the restroom from a door on the other side of the restroom.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The undulating streak is interrupted by being eclipsed by a van, also in the foreground so it isn’t as close but allows you to get a scale and helps show the undulations are not steps. They are too far apart for that. Those are caused by the headlamp wearer looking down at the path and up ahead (I think that would explain that sinusoid and also why there are only about 5 or 6 total undulations in 30 seconds.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>On the right end of that light streak the light path diverges into two separate streaks caused by (I think) the dual LEDs in the headlamp.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>OK then, now we are ready to talk about the stars. When we zoomed in on the photo, the stars were all streaks. I used this photo to explain to the scouts why this is: the earth rotates while the camera is gathering light. They weren’t sure they believed it, so I had them figure out how many degrees the earth rotates in an hour: 360 degrees divided by 24 is 15 degrees an hour. OK how much per minute? The sharp ones could divide in their heads, 15 over 60 is quarter of a degree a minute. OK how much in 30 seconds? Eighth of a degree. OK then, those stars dang sure would show as streaks, just as one guy with a headlamp (who you can’t see because he didn’t stand still long enough) made the sinusoidal streak.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>There is a fun follow up post coming soon but I gotta run. More later,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>spike<o:p></o:p></p></div></body></html>