I'm jazzed about this show. I think it'll be the most fun
planetarium show we've given so far.
We'll be showing a variety of lunarfeatures:
maria, craters, mountains, rilles, domes, catenae and more.
For each one, we'll discuss what the feature actually is and how it
was created, where to see good examples on the moon,
and -- the important part -- where you can go on Earth,
and specifically in the Western US,
to see a similar feature up close.
Plus: a short flyover of some of the major features using the
full-dome planetarium. Some features, like Tycho, the
Straight Wall, Reiner Gamma, plus lots of rilles, look really great
in the planetarium.
If you can't get to the moon yourself,
this is the next best thing!
The Hitchhiker's Guide to the Moon:
7pm at the PEEC nature center. Admission is free.
Come find out how to explore the moon without leaving your home planet!
The Mercury transit is over. But we learned some interesting things.
I'd seen Mercury transits before, but this is the first time we had an
H-alpha scope (a little 50mm Coronado PST) in addition to a white light
filter (I had my 102mm refractor set up with the Orion white-light filter).
As egress approached, Dave was viewing in the H-alpha while I was on
the white light scope. When I saw the black-drop effect at third
contact, Mercury was still nowhere near the edge in the H-alpha:
the H-alpha shows more of the solar atmosphere so the sun's image
is noticably bigger.
This was the point when we realized that we should have expected this
and been timing and recording. Alas, it was too late.
Mercury was roughly 60% out in the white light filter -- just past the
point where the "bite" it made in the limb of the sun -- by the time
Dave called out third contact. We guessed it was roughly a minute,
but that could be way off.
For fourth contact, Dave counted roughly 45 seconds between when I
couldn't see Mercury any more and when he lost track of it. This is
pretty rough, because it was windy, seeing was terrible and there
was at least a 15-second slop when I wasn't sure if I could any
indentation in the limb; I'm sure it was at least as hard in the
Coronado, which was running at much lower magnification.
So we had a chance to do interesting science and we flubbed it.
And the next chance isn't til 2032; who knows if we'll still be
actively observing then.
I wanted to at least correlate those two numbers: 45 seconds and
60% of a Mercury radius.
Mercury is about 10" (arcseconds) right now. That was easy to find.
But how fast does it move? I couldn't find anything about that,
searching for terms like mercury transit angular speed OR velocity.
I tried to calculate it with PyEphem but got a number that was orders of
magnitude off. Maybe I'll figure it out for a later article, but I wanted
to get this posted quickly.
I didn't spend much time trying photography. I got a couple afocal snaps with
my pocket digital camera through the white-light scope that worked out pretty well.
I wasn't sure that would work for the Coronado: the image is fairly dim.
The snaps I did get show Mercury, though none of the interesting detail
like faculae and the one tiny prominence that was visible. But the
interesting thing is the color. To the eye, the H-alpha scope image is
a slightly orangy red, but in the digital camera it came out a
startling purplish pink. This may be due to the digital camera's filters
passing some IR, confusing the algorithms that decide how to shift the color.
Of course, I could have adjusted the color in GIMP back to the real color,
but I thought it was more interesting to leave it the hue it came out
of the camera. (I did boost contrast and run an unsharp mask filter, to
make it easier to see Mercury.)
Anyway, fun and unexpectedly edifying! I wish we had another transit
happening sooner than 2032.
Mercury Transit 2006, photo by Brocken Inaglory
Next Monday, November 11, is a transit of Mercury across the sun.
Mercury transits aren't super rare -- not once- or twice-in-a-lifetime
transits -- but they're not that common, either.
The last Mercury transit was in 2016; the next one won't happen til 2032.
This year's transit isn't ideal for US observers. The transit will
already be well underway by the time the sun rises, at least in the
western US. Here in New Mexico (Mountain time), the sun rises with
Mercury transiting, and the transit lasts until 11:04 MST.
Everybody else, check
Mercury Transit page for your local times.
Mercury is small, unfortunately, so it's not an easy thing to see
without magnification. Of course, you know that
you should never look at the sun without an adequate filter.
But even if you have safe "eclipse glasses", it may be tough to
spot Mercury's small disk against the surface of the sun.
One option is to take some binoculars and use them to project an image.
Point the big end of the binoculars at the sun, and the small end at
a white surface, preferably leaning so it's perpendicular to the sun.
I don't know if binocular projection will give a big enough image
to show Mercury, so a very smooth and white background, tilted so
it's perpendicular to the sun, will help.
(Don't be tempted to stick eclipse glasses in front of a
binocular or telescope and look through the eyepiece! Stick to
projection unless you have filters specifically intended for
telescopes or binoculars.)
Of course, a telescope with a safe solar filter is the best way to see a
transit. If you're in the Los Alamos area, I hear the Pajarito
Astronomers are planning to set up telescopes at Overlook Park.
They don't seem to have announced it in any of the papers yet, but
I see it listed on the
There's also an event planned at the high school where the students
will be trying to time Mercury's passage, but I don't know if
that's open to the public. Elsewhere in the world, check with your local
astronomy club for Mercury transit parties: I'm sure most clubs have
I was discussing the transit with a couple of local astronomers earlier
this week, and one of them related it to the search for exoplanets.
One of the main methods of detecting exoplanets is to measure the dimming
of a star's light as a planet crosses its face.
For instance, in
55 Cancri e,
you can see a dimming as the planet crosses the star's face, and a
much more subtle dimming when the planet disappears behind the star.
As Mercury crosses the Sun's face, it blocks some of the sun's light
in the same way. By how much?
The radius of Mercury is 0.0035068 solar radii, and the dimming is
proportional to area so it should be 0.00350682, or
0.0000123, a 0.00123% dimming. Not very much!
But it looks like in the 55 Cancri e case, they're detecting dips
of around .001% -- it seems amazing that you could detect a planet
as small as Mercury this way (and certainly the planet is much bigger
in the case of 55 Cancri e) ... but maybe it's possible.
Anyway, it's fun to think about exoplanets as you watch tiny Mercury
make its way across the face of the Sun.
Wherever you are, I hope you get a chance to look!
Dave and I will be presenting a free program on Stonehenge at the Los
Alamos Nature Center tomorrow, June 14.
The nature center has a list of programs people have asked for, and
Stonehenge came up as a topic in our quarterly meeting half a year ago.
Remembering my seventh grade fascination
with Stonehenge and its astronomical alignments -- I discovered
Stonehenge Decoded at the local library, and built a desktop
model showing the stones and their alignments -- I volunteered.
But after some further reading, I realized that not all of those
alignments are all they're cracked up to be and that there might not
be much of astronomical interest to talk about, and I un-volunteered.
But after thinking about it for a bit, I realized that "not all
they're cracked up to be" makes an interesting topic in itself.
So in the next round of planning, I re-volunteered; the result is
tomorrow night's presentation.
The talk will include a lot of history of Stonehenge and its construction,
and a review of some other important or amusing henges around the world.
But this article is on the astronomy, or lack thereof.
The Background: Stonehenge Decoded
Stonehenge famously aligns with the summer solstice sunrise, and
that's when tens of thousands of people flock to Salisbury, UK to
see the event. (I'm told that the rest of the time, the monument is
fenced off so you can't get very close to it, though I've never had
the opportunity to visit.)
Curiously, archaeological evidence suggests that the summer solstice
wasn't the big time for prehistorical gatherings at Stonehenge; the
time when it was most heavily used was the winter solstice, when there's
a less obvious alignment in the other direction. But never mind that.
In 1963, Gerald Hawkins wrote an article in Nature, which he
followed up two years later with a book entitled Stonehenge Decoded.
Hawkins had access to an IBM 7090, capable of a then-impressive
100 Kflops (thousand floating point operations per second; compare
a Raspberry Pi 3 at about 190 Mflops, or about a hundred Gflops for
something like an Intel i5). It cost $2.9 million (nearly $20 million
in today's dollars).
Using the 7090, Hawkins mapped the positions of all of Stonehenge's
major stones, then looked for interesting alignments with the sun and moon.
He found quite a few of them.
(Hawkins and Fred Hoyle also had a theory about the fifty-six Aubrey
holes being a lunar eclipse predictor, which captured my seventh-grade
imagination but which most researchers today think was more likely
just a coincidence.)
But I got to thinking ... Hawkins mapped at least 38 stones if you
don't count the Aubrey holes. If you take 38 randomly distributed points,
what are the chances that you'll find interesting astronomical alignments?
A Modern Re-Creation of Hawkins' Work
Programmers today have it a lot easier than Hawkins did.
We have languages like Python, with libraries like PyEphem to handle
the astronomical calculations.
And it doesn't hurt that our computers are about a million times faster.
Anyway, my script,
takes a GPX file containing a list of geographic coordinates and compares
those points to sunrise and sunset at the equinoxes and solstices,
as well as the full moonrise and moonset nearest the solstice or equinox.
It can find alignments among all the points in the GPX file, or from a
specified "observer" point to each point in the file. It allows a slop
of a few degrees, 2 degrees by default; this is about four times the
diameter of the sun or moon, but a half-step from your observing
position can make a bigger difference than that. I don't know how
much slop Hawkins used; I'd love to see his code.
My first thought was, what if you stand on a mountain peak and look
around you at other mountain peaks? (It's easy to get GPS coordinates
for peaks; if you can't find them online you can click on them on a map.)
So I plotted the major peaks in the Jemez and Sangre de Cristo mountains
that I figured were all mutually visible. It came to 22 points; about
half what Hawkins was working with.
Yikes! Way too many. What if I cut it down? So I tried eliminating all
but the really obvious ones, the ones you really notice from across
the valley. The most prominent 11 peaks: 5 in the Jemez, 6 in the Sangres.
That was a little more manageable. Now I was down to only 22 alignments.
Now, I'm pretty sure that the Ancient Ones -- or aliens -- didn't lay
out the Jemez and Sangre de Cristo mountains to align with the rising
and setting sun and moon. No, what this tells us is that pretty much any
distribution of points will give you a bunch of astronomical alignments.
And that's just the sun and moon, all Hawkins was considering. If you
look for writing on astronomical alignments in ancient monuments,
you'll find all people claiming to have found alignments with all
sorts of other rising and setting bodies, like Sirius and
Orion's belt. Imagine how many alignments I could have found if I'd
included the hundred brightest stars.
So I'm not convinced.
Certainly Stonehenge's solstice alignment looks real; I'm not disputing that.
And there are lots of other archaeoastronomy sites that are even
more convincing, like the Chaco sun dagger. But I've also seen plenty of
web pages, and plenty of talks, where someone maps out a collection of
points at an ancient site and uses alignments among them as proof that
it was an ancient observatory. I suspect most of those alignments are more
evidence of random chance and wishful thinking than archeoastronomy.
Last night, as we drove home from the
-- one of Los Alamos's best annual events, a night exhibition of
dozens of carved pumpkins all together in one place -- I noticed a
glow on the horizon right around Truchas Peak and wondered if the moon
was going to rise that far north.
Sure enough, I saw the first sliver of the moon poking over the peak
as we passed the airport. "We may get an extended moonrise tonight",
I said, realizing that as the moon rose, we'd be descending the
"Main Hill Road", as that section of NM 502 is locally known, so we'd
get lower with respect to the mountains even as the moon got higher.
Which would win?
As it turns out, neither. The change of angle during the descent down
the Main Hill Road exactly matches the rate of moonrise, so the size
of the moon's sliver stayed almost exactly the same during the whole
descent, until we got down to the "Y" where a nearby mesa blocked our
view entirely. By the time we could see the moon again, it was just
freeing itself of the mountains.
Neat! Made me think of The Little Prince: his home asteroid B6-12
(no, that's not a real asteroid desgination) was small enough that by
moving his chair, he could watch sunset over and over again.
I'm a sucker for moonrises -- and now I know how I can make them last
Dave and I are giving a planetarium show at PEEC tonight on the analemma.
I've been interested in the analemma for years and have
written about it before,
here on the blog
and in the SJAA Ephemeris.
But there were a lot of things I still didn't understand as well as
I liked. When we signed up three months ago to give this talk, I had
plenty of lead time to do more investigating, uncovering lots of
interesting details regarding the analemmas of other planets,
the contributions of the two factors that go into the Equation of Time,
why some analemmas are figure-8s while some aren't,
and the supposed "moon analemmas" that have appeared on the
of the Day. I added some new features to the analemma script I'd
written years ago as well as corresponding with an expert who'd written
some great Equation of Time code for all the planets. It's been fun.
I'll write about some of what I learned when I get a chance, but
meanwhile, people in the Los Alamos area can hear all about it
tonight, at our PEEC show:
The Analemma Dilemma,
7 pm tonight, Friday Feb 23, at the Nature Center,
admission $6/adult, $4/child.
My first total eclipse! The suspense had been building for years.
Dave and I were in Wyoming. We'd made a hotel reservation nine months
ago, by which time we were already too late to book a room in the zone
of totality and settled for Laramie, a few hours' drive from the centerline.
For visual observing, I had my little portable 80mm refractor. But
photography was more complicated. I'd promised myself that for my
first (and possibly only) total eclipse, I wasn't going to miss the
experience because I was spending too much time fiddling with cameras.
But I couldn't talk myself into not trying any photography at all.
I spent several weeks before the eclipse in a flurry of creation,
making a couple of
mount, and then wrestling with motorizing the barn-door (which was
a failure because I couldn't find a place to buy decent gears for the motor.
I'm still working on that and will eventually write it up).
I wrote up a plan: what equipment I would use when, a series of
progressive exposures for totality, and so forth.
And then, a couple of days before we were due to leave, I figured I
should test my rig -- and discovered that it was basically impossible
to focus on the sun. For the Venus transit, the sun wasn't that high
in the sky, so I focused through the viewfinder. But for the total
eclipse, the sun would be almost overhead, and the viewfinder nearly
impossible to see. So I had planned to point the Mak at a distant
hillside, focus it, then slip the filter on and point it up to the sun.
It turned out the focal point was completely different through the filter.
With only a couple of days left to go, I revised my plan.
The Mak is difficult to focus under any circumstances. I decided
not to use it, and to stick to my Canon 55-250mm zoom telephoto,
with the camera on a normal tripod. I'd skip the partial eclipse
(I've photographed those before anyway) and concentrate on
getting a few shots of the diamond ring and the corona, running
through a range of exposures without needing to look at the camera
screen or do any refocusing. And since I wasn't going to be usinga
telescope, my nifty solar finders wouldn't work; I designed a new
one out of popsicle sticks to fit in the camera's hot shoe.
We stayed with relatives in Colorado Saturday night, then drove to
Laramie Sunday. I'd heard horror stories of hotels canceling people's
longstanding eclipse reservations, but fortunately our hotel honored
our reservation. WHEW! Monday morning, we left the hotel at 6am in
case we hit terrible traffic. There was already plenty of traffic on
the highway north to Casper, but we turned east hoping for fewer crowds.
A roadsign sign said "NO PARKING ON HIGHWAY." They'd better not try
to enforce that in the totality zone!
When we got to I-25 it was moving and, oddly enough, not particularly
crowded. Glendo Reservoir had looked on the map like a nice spot on
the centerline ... but it was also a state park, so there was a risk
that everyone else would want to go there. Sure enough: although
traffic was moving on I-25 at Wheatland, a few miles north the freeway
came to a screeching halt. We backtracked and headed east toward Guernsey,
where several highways went north toward the centerline.
East of Glendo, there were crowds at every highway pullout and rest
stop. As we turned onto 270 and started north, I kept an eye on
OsmAnd on my phone, where I'd loaded
a GPX file of the eclipse path. When we were within a mile of the
centerline, we stopped at a likely looking pullout. It was maybe 9 am.
A cool wind was blowing -- very pleasant since we were expecting a hot
day -- and we got acquainted with our fellow eclipse watchers as we
waited for first contact.
Our pullout was also the beginning of a driveway to a farmhouse we could
see in the distance. Periodically people pulled up, looking lost,
checked maps or GPS, then headed down the road to the farm. Apparently
the owners had advertised it as an eclipse spot -- pay $35, and you
can see the eclipse and have access to a restroom too! But apparently
the old farmhouse's plumbing failed early on, and some of the people
who'd paid came out to the road to watch with us since we had better
equipment set up.
There's not much to say about the partial eclipse. We all traded views
-- there were five or six scopes at our pullout, including a nice
little H-alpha scope. I snapped an occasional photo through the 80mm
with my pocket camera held to the eyepiece, or with the DSLR through
an eyepiece projection adapter. Oddly, the DSLR photos came out worse
than the pocket cam ones. I guess I should try and debug that at some point.
Shortly before totality, I set up the DSLR on the tripod, focused on a
distant hillside and taped the focus with duct tape, plugged in the
shutter remote, checked the settings in Manual mode, then set the
camera to Program mode and AEB (auto exposure bracketing). I put the
lens cap back on and pointed the camera toward the sun using the
popsicle-stick solar finder. I also set a countdown timer, so I could
press START when totality began and it would beep to warn me when it was
time to the sun to come back out. It was getting chilly by then, with
the sun down to a sliver, and we put on sweaters.
The pair of eclipse veterans at our pullout had told everybody to
watch for the moon's shadow racing toward us across the hills from the
west. But I didn't see the racing shadow, nor any shadow bands.
And then Venus and Mercury appeared and the sun went away.
One thing the photos don't prepare you for is the color of the sky. I
expected it would look like twilight, maybe a little darker; but it
was an eerie, beautiful medium slate blue. With that unworldly
solar corona in the middle of it, and Venus gleaming as bright as
you've ever seen it, and Mercury shining bright on the other side.
There weren't many stars.
We didn't see birds doing anything unusual; as far as I can tell,
there are no birds in this part of Wyoming. But the cows did all
get in a line and start walking somewhere. Or so Dave tells me.
I wasn't looking at the cows.
Amazingly, I remembered to start my timer and to pull off the DSLR's
lens cap as I pushed the shutter button for the diamond-ring shots
without taking my eyes off the spectacle high above. I turned the
camera off and back on (to cancel AEB), switched to M mode, and
snapped a photo while I scuttled over to the telescope, pulled the
filter off and took a look at the corona in the wide-field eyepiece.
So beautiful! Binoculars, telescope, naked eye -- I don't know which
view was best.
I went through my exposure sequence on the camera, turning the dial a
couple of clicks each time without looking at the settings, keeping my
eyes on the sky or the telescope eyepiece. But at some point I happened
to glance at the viewfinder -- and discovered that the sun was drifting
out of the frame. Adjusting the tripod to get it back in the frame
took longer than I wanted, but I got it there and got my eyes
back on the sun as I snapped another photo ...
and my timer beeped.
I must have set it wrong! It couldn't possibly have been two
and a half minutes. It had been 30, 45 seconds tops.
But I nudged the telescope away from the sun, and looked back up -- to
another diamond ring. Totality really was ending and it was time to
The trip back to Golden, where we were staying with a relative, was
hellish. We packed up immediately after totality -- we figured we'd
seen partials before, and maybe everybody else would stay. No such luck.
By the time we got all the equipment packed there was already a steady
stream of cars heading south on 270.
A few miles north of Guernsey the traffic came to a stop. This was to
be the theme of the afternoon. Every small town in Wyoming has a stop sign
or signal, and that caused backups for miles in both directions.
We headed east, away from Denver, to take rural roads down through
eastern Wyoming and Colorado rather than I-25, but even so,
we hit small-town stop sign backups every five or ten miles.
We'd brought the Rav4 partly for this reason. I kept my eyes glued on
OsmAnd and we took dirt roads when we could, skirting the paved
highways -- but mostly there weren't any dirt roads going where we
needed to go. It took about 7 hours to get back to Golden, about twice
as long as it should have taken. And we should probably count
ourselves lucky -- I've heard from other people who took 11 hours to
get to Denver via other routes.
Dave is fond of the quote,
"No battle plan survives contact with the enemy"
(which turns out to be from Prussian military strategist
von Moltke the Elder).
The enemy, in this case, isn't the eclipse; it's time.
Two and a half minutes sounds like a lot, but it goes by like nothing.
Even in my drastically scaled-down plan, I had intended exposures from
1/2000 to 2 seconds (at f/5.6 and ISO 400). In practice, I only made
it to 1/320 because of fiddling with the tripod.
And that's okay. I'm thrilled with the photos I got, and definitely
wouldn't have traded any eyeball time for more photos. I'm more annoyed
that the tripod fiddling time made me miss a little bit of extra looking.
My script actually worked out better than I expected, and I was very
glad I'd done the preparation I had. The script was reasonable, the
solar finders worked really well, and the lens was even in focus
for the totality shots.
Then there's the eclipse itself.
I've read so many articles about solar eclipses as a mystical,
religious experience. It wasn't, for me. It was just an eerily
beautiful, other-worldly spectacle: that ring of cold fire staring
down from the slate blue sky, bright planets but no stars, everything
strange, like nothing I'd ever seen. Photos don't get across what it's
like to be standing there under that weird thing in the sky.
I'm not going to drop everything to become a globe-trotting eclipse
chaser ... but I sure hope I get to see another one some day.
While I was testing various attempts at motorizing my barn-door mount,
trying to get it to track the sun, I had to repeatedly find the sun
in my telescope.
In the past, I've generally used the shadow of the telescope combined
with the shadow of the finderscope. That works, more or less, but it's
not ideal: it doesn't work as well with just a telescope with no finder,
which includes both of the scopes I'm planning to take to the eclipse;
and it requires fairly level ground under the telescope: it doesn't
work if there are bushes or benches in the way of the shadow.
For the eclipse, I don't want to waste any time finding the sun:
I want everything as efficient as possible. I decided to make a little
solar finderscope. One complication, though: since I don't do solar
observing very often, I didn't want to use tape, glue or, worse, drill
holes to mount it.
So I wanted something that could be pressed against the telescope and
held there with straps or rubber bands, coming off again without
leaving a mark. A length of an angled metal from my scrap pile
seemed like a good size to be able to align itself against a small
Then I needed front and rear sights. For the front sight, I wanted a
little circle that could project a bulls-eye shadow onto a paper card
attached to the rear sight. I looked at the hardware store for small
eye-bolts, but no dice. Apparently they don't come that small.I
settled for the second-smallest size of screw eye.
The screw eye, alas, is meant to screw into wood, not metal. So I
cut a short strip of wood a reasonable size to nestle into the inside
of the angle-iron. (That ripsaw Dave bought last year sure does come
in handy sometimes.) I drilled some appropriately sized holes and
fastened screw eyes on both ends, adding a couple of rubber grommets
as spacers because the screw eyes were a little too long and I didn't
want the pointy ends of the screws getting near my telescope tube.
I added some masking tape on the sides of the angle iron so it wouldn't
rub off the paint on the telescope tube, then bolted a piece of
cardboard cut from an old business card to the rear screw eye.
Voila! A rubber-band-attached solar sight that took about an hour to make.
Notice how the shadow of the front sight exactly fits around the rear
sight: you line up the shadow with the rear sight to point the scope.
It seems to work pretty well, and it should be adaptable to any
telescope I use.
I used a wing nut to attach the rear cardboard: that makes it easy to
replace it or remove it. With the cardboard removed,
the sight might even work for night-time astronomy viewing. That is,
it does work, as long as there's enough ambient light to see the rings.
Hmm... maybe I should paint the rings with glow-in-the-dark paint.