Tuesday, October 4, 2016

Update / Erratum on "What IS that below?" (height above the horizon; photos of an arrow)


I forgot about something in my answer yesterday. When you look for the Farallons, you have to think about WHERE you're standing.  

In the original Challenge I asked:  And where should I stand?

That's an important part of the question.  If you're standing on the beach at the westernmost edge of San Francisco, your eyes might be only 5 feet above sea level.  A quick search for information about the horizon leads us to this equation to compute the visual distance to the horizon.  Here, d is the distance of the horizon (in miles) if your eyes are h feet above the ground.  (The squiggly line symbol means "nearly equal to.") 

So, if your eyes are 5 feet above the ground, the horizon seems to be 2.72 miles away.  That is, your 5-foot-high eyes can see an island on the sea that's 2.72 miles away.  

As I noted, this picture of the islands was shot from Twin Peaks, a local mountain in the western part of San Francisco.  

If you're standing on Twin Peaks (at a height of 922 feet), the apparent horizon is 37 miles.   So how far are the Farallons from Twin Peaks?  I used Google Maps to measure the distance and found this: 

Since the islands are 30 miles from Twin Peaks, it's easy to see them on the horizon (with a decent telephoto lens and clear air).  

To see the Farallons from the closest beach (which is 27 miles from the Farallons), you'd have to have your eyes at (27/1.22)2  =  489 feet in the air.  That's a mighty tall ladder.  

Okay.  I admit my blunder, and have set the record straight.  (Tip of the hat to Don Norman for pointing this out!)  

In other news...  

I just coincidentally (really) happen to be St. George, Utah to give a talk today at Dixie State University.  

As I mentioned in yesterday's post, one of the Transcontinental Airmail arrows happens to be here.  So I popped out there today to take a few pics.  

Note the steel L-beam still sticking up out of the concrete.
It was one of the legs of the light tower over the concrete arrow.
St. George is off in the distance.

A selfie while sitting on the point of the arrow.
A nice monument marker placed by the arrow by the Sons of Utah Pioneers.


  1. Good Morning, Dr. Russell.

    When you asked "and where should I stand?" I thought you meant a place or location. So this answer teach me another lesson and is great to know it.

    And the photos are great. Glad you could be next to one in real life. That is one of many reasons why your Challenges are so great. Once we find something online, we can touch it in real life! Plus the knowledge stays forever.

    About other Challenges, I was watching Trust me I am a Doctor and episode showed this about proteins Will protein supplements help me put on more muscle? Also mentioned that anti-oxidants really don't work versus Vitamin C. Even more, they increase at the moment your levels and then the body works to lower that level and maintain stable level.

  2. Bay Search: the long view & the twisted view.
    while looking for potential vantage points to view the off-shore Farallones, I consulted the noted authority on all things Bayistic…
    Dr. D. Michael Hasselhoff, who pointed me toward the far less known granite protrusions off India Basin, in the Bay… he said sightings
    of "Los dientes de leche del diablo" are rarer than Yeti encounters, but they do occur and are spectacular during the fleeting moments they exist…
    often immediately preceding or following encounters with Karl the Fog.
    (sometimes they are called "satan's lil niblets").
    They are almost the same distance from the GooglePlex that the oceanic isles are from Twin Peaks… so in theory you might be able to spot them
    with enough altitude - read new GoPro Karma - without leaving your office. You might keep an eye out…

    four supporting images… of varying veracity:
    off India Basin
    mini-bay Farallones
    India Basin Shoreline Park… obviously a favorite PegPerson hangout
    9/23 webcam proof of habitation…

    Horizon SERP
    Horizon wiki
    boat example

    Break, break, break
    On thy cold gray stones, O Sea!
    And I would that my tongue could utter
    The thoughts that arise in me.

    Alfred Lord Tennyson, Poet, 1842

    Wave breaks over Sea Lion Islet at Farallon National Wildlife Refuge
    the owls
    "Can you imagine the entire marine terrace covered in fur seals? That’s the way it used to be. As fur seal numbers continue to rise sea lions will get pushed out, like the ones in our front yard this fall.
    Fur seals have come a long way back from the days of the California “fur rush.” But they still have a long way to go to establish a population that resembles anything close to historic levels. Globally they remain a vulnerable species, as listed by the IUCN. Here’s hoping that fur seals can continue to thrive in the face of an uncertain future! "

    fur seals
    life & death
    India Basin Open Space - remarkably trashy, favorite burn-out location
    India Basin Shoreline Park - also litter-riffic, thumbs up SF
    nice overview from 2010

    1. Cute, Remijj. I especially like the last link to the KQED documentary about the Farallones.