[pasmembers] Fw: Question about solar eclipse
- From: LPhxAZ <lphxaz@xxxxxxxxx>
- To: "List Serv" <pasmembers@xxxxxxxxxxxxx>
- Date: Thu, 17 May 2012 06:54:42 -0700
if anyone is interested, I am forwarding some eclipse viewing tips that I
recently sent to a teacher
----- Original Message -----
From: LPhxAZ
To: Alison Thammavongsa
Sent: Thursday, May 17, 2012 6:45 AM
Subject: Re: Question about solar eclipse
Dear Alison,
suggestions for safe viewing: http://mreclipse.com/Totality2/TotalityCh11.html
in the section on pinhole projection method, where they mention "two thin but
stiff pieces of white cardboard" - paper plates are very good for this.
remember to stand with your back to the Sun when using this. you can practice
on a non-eclipse day.
another projection method, not listed in the article is: look on the ground
under a tree. the spaces between the leaves form many pinholes, and you will
see a whole bunch of crescents as the sun is eclipsed. makes a great photo!
http://www.hartrao.ac.za/other/eclipse2002/pinhole.html
and here is another link I found that you can share with your students,
including step-by-step instructions for making a pinhole projection viewer:
http://www.exploratorium.edu/eclipse/how.html
I tried several different methods of pinhole projection, and found that the
"two pieces of cardboard" is easiest to use and gives the best results - even
better than the one with the UPS tube in the exploratorium article.
paper plates work well and are easily available, but I used box lids from a
case of copy paper. or you can use the sides of a cut-up carton, or a shoebox
and its lid, etc etc.
you can even punch holes in a pattern (e.g. I made one where the pinholes are
arranged to show the number 2012) and when you use it during the eclipse - each
pinhole will show a view of the eclipsed Sun. great photo-op!
if using a pinhole projector, it's a good idea to prepare it ahead of time, and
try it out before the eclipse. you can try different size pinholes (anywhere
from very tiny, to about 1/8 inch) and see what gives you the best effect. I
made one with actual pinholes, and another with pinholes enlarged using a
sharpened pencil (that's for the 1/8 inch). you don't need to use aluminum
foil - I made the pinholes directly in the cardboard. (and if you make one in
the wrong place, just cover it with a small piece of paper or posterboard.)
besides testing the pinhole projectors outside, I also tested them with a
flashlight in a darkened room, to make sure that what I was seeing was an image
and not just a circle of diffuse light projected through a circular opening.
you can also test them by using them when the Sun is partly hidden by a tree or
building, and then you can see that you are getting an image and not just a
circle of light.
please go ahead and share this with your students!
best regards,
Leah
From: LPhxAZ [mailto:lphxaz@xxxxxxxxx]
Sent: Wednesday, May 09, 2012 12:40 PM
To: Alison Thammavongsa
Cc: Terri Finch; Don Boyd
Subject: Re: Question about solar eclipse
it is an unusual type of eclipse called an "annular" eclipse. this means
that even when the Moon is directly in front of the Sun, the Sun is not
completely covered, but a bright ring is still visible around the edge. (and
this means that eye protection is necessary, even in locations of maximum
eclipse.)
the reason that this happens: in general, the diameter of the Sun is
about 400 times that of the Moon; but the Sun is also 400 times as far away.
as a result, they both appear to be about the same size in the sky, and when
the Moon passes in front of the Sun, it covers it completely. this is a total
eclipse.
but the orbits of the Earth and Moon are not perfectly circular; they are
slightly elliptic. depending on where it is in its orbit, the Earth can be a
bit closer or a bit farther from the Sun than 93 million miles (anywhere from
91.4 to 94.5 million); and the Moon can be a bit closer or a bit farther from
the Earth than 240,000 miles (anywhere from 223,000 to 254,000). so, if an
eclipse happens (i.e. the Sun, Moon and Earth are all in a straight line) at
one of the times when the Earth is closer to the Sun (i.e. the Sun will look
slightly larger), and the Moon is farther from the Earth (i.e. the Moon will
look slightly smaller) then the Moon will not completely cover the Sun even at
maximum eclipse, and we get an annular eclipse. the sky doesn't go dark as it
does in a total eclipse, but it is still very interesting to watch -
particularly because it is a rare event.
Flagstaff is on the edge of the maximum eclipse path; and Phoenix is a
little farther away. and so, at the center of the maximum eclipse path, the
eclipse will be about 96%; in Flagstaff, 93%; and in Phoenix, 89%. I
personally am going to be driving to the Grand Canyon and participating as a
volunteer in showing the eclipse, and also showing the sky later that night:
http://www.nps.gov/grca/planyourvisit/annular201205.htm. but that is because
the Grand Canyon is such a special, beautiful place to be, and I want to be
there for this special event. otherwise I wouldn't travel so far just for a
few extra percentage points. (btw at the Grand Canyon it will be about 94.5%.)
wishing you clear skies and happy observing, wherever you choose to be!
and don't forget the eye protection!
From: LPhxAZ [mailto:lphxaz@xxxxxxxxx]
Sent: Monday, April 16, 2012 1:02 PM
To: Alison Thammavongsa
Cc: Terri Finch
Subject: Re: Question about Venus Transit
the eclipse will begin at 5:30 pm on Sunday May 20, maximum eclipse at
6:40 pm, and the end of the eclipse at 7:40 pm.
sunset is at 7:26, so the sun will disappear from view a little bit
before the actual end of the eclipse. but the ending stages of the eclipse are
just like the beginning stages, just in reverse. so missing the last few
minutes isn't a big deal.
the Venus transit will begin at 3:09 pm on Tuesday June 5, and will
continue past sunset (till around 10 pm, if we could see it). Venus will be
about 2/3 of the way across when the sun sets at 7:36 pm.
you don't need a telescope for the eclipse - just some kind of eye
protection or a projection technique, such as a pinhole projector, as described
in the links I sent earlier.
but because Venus is so small compared to the Sun, you do need a
telescope (with a solar filter, of course) to be able to see the transit. so,
that is a good reason to bring your students to the PAS Star Party at PVCC for
the transit.
From: LPhxAZ [mailto:lphxaz@xxxxxxxxx]
Sent: Monday, April 09, 2012 4:00 PM
To: Terri; Alison Thammavongsa
Subject: Re: Question about Venus Transit
Venus transits occur in pairs, once in 120 years. the two transits
of each pair are 8 years apart. so, there was one in 2004, and this is the
second one (2012, eight years after the previous one).
the next pair of Venus transits will be in 2117 and 2125.
you can read more about Venus transits here:
http://en.wikipedia.org/wiki/Transit_of_Venus
Mercury transits happen more often. we viewed one in Phoenix in Nov
2006. the next ones will be in 2016 and 2019. more information here:
http://en.wikipedia.org/wiki/Transit_of_Mercury
regarding the solar eclipse:
the current one is a special type of partial eclipse called an
"annular eclipse". it will be around 88% in Phoenix and 96% in the maximum
areas (which will include northern Arizona).
you can read more about eclipses here:
http://mreclipse.com/Special/SEprimer.html
here are some suggestions for safe viewing:
http://mreclipse.com/Totality2/TotalityCh11.html
in the section on pinhole projection method, where they mention "two
thin but stiff pieces of white cardboard" - paper plates are very good for
this. remember to stand with your back to the Sun when using this. you can
practice on a non-eclipse day.
another projection method, not listed in the article is: look on
the ground under a tree. the spaces between the leaves form many pinholes, and
you will see a whole bunch of crescents as the sun is eclipsed.
http://www.hartrao.ac.za/other/eclipse2002/pinhole.html
the next solar eclipse visible in the US will be in August 2017. the
path of totality will cross the US from Oregon to South Carolina. I highly
recommend travelling to see this one - a total eclipse is an amazing
experience. here is an interactive map:
http://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2017Aug21Tgoogle.html
the 2017 eclipse will be visible in Arizona as a partial (around 70%)
eclipse.
Other related posts:
- » [pasmembers] Fw: Question about solar eclipse - LPhxAZ
