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| Stills from "Black Like Me" |
Monday, April 21, 2014
Friday, April 18, 2014
Wednesday, April 16, 2014
Tampa's Pride
[Commissioner] Victor Crist unsuccessfully sought formal assurances that the vote would not result in Hillsborough County supporting obscene, prurient events not appropriate for families.
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| Gasparilla 1968 Florida Archives |
"The festivals, the activities and things need to have a little different tone to them," said Crist, a Republican. "Parading around in lingerie, pasties, g-strings and outfits that promote your sexual organs is not necessarily an appropriate thing to do in Hillsborough County."
"That's Gasparilla," a member of the audience replied, bringing laughter.
June 5, 2013 Tampa Bay Times
Saturday, April 5, 2014
Solar Mysteries Resolved
If you're reading this please send me a note. I hate lurkers. I really, really hate them. That said, I'm now going to experiment with producing original content:
Mystery #1: The ultraviolet "danger zone"
The ultraviolet "danger times" are often given as "2 hours before and 4 hours after noon." This could lead a reasonable person to presume that UV is somehow less dangerous in the morning than it is in the afternoon. The reality is the recommendation has more to do with politics than it does with science.
Science tells us the danger period is roughly 2 hours before and after solar noon. Solar noon rarely occurs at the same time as noon on a standard clock for several reasons. For one, the time zones have been re-drawn for political reasons so it's possible for you to live in a place that's very far from the longitude nearest to your solar noon time. Second, even after correcting for time zones, solar noon itself varies throughout the year by up to 30 minutes thanks to our elliptical orbit and a few other factors. So to account for this the CDC bumped up the times to 3 hours before and after clock noon as a rule-of-thumb.
The problem most relevant to the morning/afternoon asymmetry, however, is that we observe Daylight Saving Time in the U.S. during most of the year, which puts solar noon off by an additional hour for most people. Instead of expanding the danger times further, the CDC simply shifted them ahead by one hour to match DST. This is probably best because UV tends to get more press coverage in the summer months, and after all it's only a rule-of-thumb. OK, but a rule-of-thumb that can lead reasonable people to form erroneous assumptions about the sun. Furthermore, UV can actually be more dangerous in winter, particularly at high altitudes and in the presence of snow.
Mystery #2: The sun overhead
While walking home the other day I was irritated that the sun appeared to be shining on the north sides of buildings as I passed by. It was my understanding that when one lives above the tropic of cancer the sun is never directly overhead. I interpreted this to mean that buildings north of the tropics must always have a shadow on their north face. I happened to know the street I was walking on was built along a TRS line, however, and therefore was very precisely a north-south road. So, what was going on?
It turns out my interpretation is only partially correct. A building north of the tropics will only always have a shadow at solar noon. On the summer solstice in Tampa this shadow can be as small as 5 degrees as measured from the top of the building. As the sun sweeps an arc across the sky on the solstice, its compass position can pass up to 28 degrees north of the east-west line. This occurs from 6:30 AM to 11:00 AM and from 4:00 PM to 8:30 PM on that day, when its azimuth is less than 90 or greater than 270 degrees, and its elevation is less than 60 degrees.
So on summer evenings in Tampa there is likely more shade to be found on the south side of a building than there is on the north side, a handy thing to know for people who fear the sun.
Mystery #3: The analemma
A circle has one center, an ellipse has two. Our orbit around the sun is an ellipse with two centers. The sun occupies one center, and the other is empty space. The gravity of the sun is what's swinging us around the ellipse, however, and so we are moving faster when we're closer to it, and slower when we're closer to empty space.
An analemma is a plot of where the sun appears in the sky at clock noon every day for a year. The distance from the top to the bottom of the chart represents the distance between the tropics of capricorn and cancer. Using the chart we can tell when the apparent motion of the sun in the sky is moving "fast" or "slow" and therefore gives us an earlier or later solar noon reading relative to clock time.
It also happens that the analemma forms a pleasant shape which is suitable for placing on the sides of globes, particularly in the vast boring empty stretches around the Pacific ocean. It also makes for a neat year-long composite camera image for people with patience and good timing.
Mystery #4: UVA is NOT harmless, and it's everywhere
UVC is the nightmare radiation that seeps through the ozone hole. Most people don't get this without cooking themselves nude on a beach at solar noon on the summer solstice. UVB is the more familiar type that causes sunburn when you stay out too long without sunscreen on a sunny day.
UVA, however, is the stuff that goes right through your sunscreen, your clothes, and into the deeper layers of your skin. It goes through clouds, it goes through glass, it goes through just about everything that isn't opaque. Furthermore, because it penetrates the skin it is the radiation that causes the wonderful long-lasting deep glowing tan hawked as "safe" by tanning salons. The problem is because it operates at the structural level of the skin, it tends to cause the sort of loosening and wrinkling damage associated with aged skin. Second, if you're going to get cancer from ultraviolet exposure, then you want to have it on the surface where UVB operates, because those tumors are slow-growing and easily removed. If you get cancer deep in your skin, then it will often grow faster, making it harder to get at and remove before it spreads to other body parts and kills you.
Now for the freaky part. UVA is EVERYWHERE. You cannot escape it. If you can see light, even if it's an artificial light, then you're probably getting a measurable dose of UVA. If there is enough sun outside to necessitate wearing sunglasses, then you're probably getting dosed with UVA and B. If you're watching the sunset you're getting UVA. If you're working under fluorescent lights you're getting UVA. If you're staring at a monitor, then UVA could be getting into your eyes (such screens are normally polarized...I don't know how that affects it) My feeling is the new LED bulbs in the warm range probably emit the least UVA, but I don't know for sure. I'm also unclear on which bits of the spectrum are more likely to be reflected off cement pavement, or that will bounce around the margins of curtains to get inside your home.
Mystery #1: The ultraviolet "danger zone"
The ultraviolet "danger times" are often given as "2 hours before and 4 hours after noon." This could lead a reasonable person to presume that UV is somehow less dangerous in the morning than it is in the afternoon. The reality is the recommendation has more to do with politics than it does with science.
Science tells us the danger period is roughly 2 hours before and after solar noon. Solar noon rarely occurs at the same time as noon on a standard clock for several reasons. For one, the time zones have been re-drawn for political reasons so it's possible for you to live in a place that's very far from the longitude nearest to your solar noon time. Second, even after correcting for time zones, solar noon itself varies throughout the year by up to 30 minutes thanks to our elliptical orbit and a few other factors. So to account for this the CDC bumped up the times to 3 hours before and after clock noon as a rule-of-thumb.
The problem most relevant to the morning/afternoon asymmetry, however, is that we observe Daylight Saving Time in the U.S. during most of the year, which puts solar noon off by an additional hour for most people. Instead of expanding the danger times further, the CDC simply shifted them ahead by one hour to match DST. This is probably best because UV tends to get more press coverage in the summer months, and after all it's only a rule-of-thumb. OK, but a rule-of-thumb that can lead reasonable people to form erroneous assumptions about the sun. Furthermore, UV can actually be more dangerous in winter, particularly at high altitudes and in the presence of snow.
Mystery #2: The sun overhead
While walking home the other day I was irritated that the sun appeared to be shining on the north sides of buildings as I passed by. It was my understanding that when one lives above the tropic of cancer the sun is never directly overhead. I interpreted this to mean that buildings north of the tropics must always have a shadow on their north face. I happened to know the street I was walking on was built along a TRS line, however, and therefore was very precisely a north-south road. So, what was going on?
It turns out my interpretation is only partially correct. A building north of the tropics will only always have a shadow at solar noon. On the summer solstice in Tampa this shadow can be as small as 5 degrees as measured from the top of the building. As the sun sweeps an arc across the sky on the solstice, its compass position can pass up to 28 degrees north of the east-west line. This occurs from 6:30 AM to 11:00 AM and from 4:00 PM to 8:30 PM on that day, when its azimuth is less than 90 or greater than 270 degrees, and its elevation is less than 60 degrees.
So on summer evenings in Tampa there is likely more shade to be found on the south side of a building than there is on the north side, a handy thing to know for people who fear the sun.
Mystery #3: The analemma
A circle has one center, an ellipse has two. Our orbit around the sun is an ellipse with two centers. The sun occupies one center, and the other is empty space. The gravity of the sun is what's swinging us around the ellipse, however, and so we are moving faster when we're closer to it, and slower when we're closer to empty space.
An analemma is a plot of where the sun appears in the sky at clock noon every day for a year. The distance from the top to the bottom of the chart represents the distance between the tropics of capricorn and cancer. Using the chart we can tell when the apparent motion of the sun in the sky is moving "fast" or "slow" and therefore gives us an earlier or later solar noon reading relative to clock time.
It also happens that the analemma forms a pleasant shape which is suitable for placing on the sides of globes, particularly in the vast boring empty stretches around the Pacific ocean. It also makes for a neat year-long composite camera image for people with patience and good timing.
Mystery #4: UVA is NOT harmless, and it's everywhere
UVC is the nightmare radiation that seeps through the ozone hole. Most people don't get this without cooking themselves nude on a beach at solar noon on the summer solstice. UVB is the more familiar type that causes sunburn when you stay out too long without sunscreen on a sunny day.
UVA, however, is the stuff that goes right through your sunscreen, your clothes, and into the deeper layers of your skin. It goes through clouds, it goes through glass, it goes through just about everything that isn't opaque. Furthermore, because it penetrates the skin it is the radiation that causes the wonderful long-lasting deep glowing tan hawked as "safe" by tanning salons. The problem is because it operates at the structural level of the skin, it tends to cause the sort of loosening and wrinkling damage associated with aged skin. Second, if you're going to get cancer from ultraviolet exposure, then you want to have it on the surface where UVB operates, because those tumors are slow-growing and easily removed. If you get cancer deep in your skin, then it will often grow faster, making it harder to get at and remove before it spreads to other body parts and kills you.
Now for the freaky part. UVA is EVERYWHERE. You cannot escape it. If you can see light, even if it's an artificial light, then you're probably getting a measurable dose of UVA. If there is enough sun outside to necessitate wearing sunglasses, then you're probably getting dosed with UVA and B. If you're watching the sunset you're getting UVA. If you're working under fluorescent lights you're getting UVA. If you're staring at a monitor, then UVA could be getting into your eyes (such screens are normally polarized...I don't know how that affects it) My feeling is the new LED bulbs in the warm range probably emit the least UVA, but I don't know for sure. I'm also unclear on which bits of the spectrum are more likely to be reflected off cement pavement, or that will bounce around the margins of curtains to get inside your home.
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