Successful Selenelion, Mt. Laguna, CA, Sept. 27, 2015

Tony Crocker

Staff member
There was a total lunar eclipse visible from North America last Sunday evening. Since the partial eclipse would be in progress at local sunset, I wanted to try for a selenelion, where the sun and eclipsed moon can be seen simultaneously on opposite horizons. Finding a spot with unobstructed east and west horizons required some Google Earth research. Around L.A. it seems difficult as most mountain ranges run on an east/west axis. And I wasn't willing to climb something like Mt. Baden-Powell where I would have to hike down a couple of hours after dark.

So I concentrated on San Diego County where the mountains run north/south and finally chose Mt. Laguna, which showed a drive-up paved road about 15 miles northeast of Interstate 8 at 6,000 feet. I arrived a bit after 5PM at a small parking area overlooking the eastern desert view where the moon would rise. There were already about 8 cars there and a couple of scopes set up. However it was still 20 feet or so below the bushy ridgeline blocking the western view. The road continued along the ridge but was blocked by a gate. So I headed up the road on foot to a fenced radar installation, and fortunately the area next to the fence was mostly bare gravel and had the unobstructed views both ways that I was seeking. I texted instructions to my friends Jack and Leslie Vaughn joining me and they got up there a little after 6PM. Another group is setting up here on the eastern edge.

I took this picture for Samantha nostalgia. These 2 yellow labs were about 3 years old.

In nearby Julian moonrise was 6:31 and sunset was 6:36, the difference being due to atmospheric refraction. I figured we might get an extra 5 minutes each way with views to sea level from 6,000 feet. The desert had no clouds but a brownish dusty horizon so we probably needed the extra time. The air was clearer to the west with thin clouds near the ocean that the sun would probably shine through.

So we lined up compasses and stared intently due east starting around 6:25. Leslie first spotted the partial eclipsed moon above the desert haze starting at 6:32 but it did not show up in pictures until about 6:35.

Moon pics did not get much sharper until 6:39.

Sun 6:40

Moon 6:40

Sunset was at 6:41 about as I expected.

Jack used the iPhone panorama feature to capture moon and sun in the same picture.

FTO Resolution is not great. You have to know where the moon is so I circled it.

So we had 9 minutes of visible selenelion with the partial eclipse. It's an open question how long the eclipse would have been visible over the desert if selenelion had occurred during the darker total phase.

Moon was sharper at 6:48.

But it's still pink from the low angle view over the desert. This is different from the rust/orange color seen when the eclipse is total.

Here we are a few minutes later, with the now white partial eclipse above Leslie's head.

We have had a very hot September in SoCal. Even at 6,000 feet it was about 80F when I arrived and 70F when we left after 8PM. It was breezy so we moved to the leeward east side of the ridge on the road to view totality starting 7:11. This was a very dark eclipse, mostly gray with just a hint of the usual orange. The Danjon1 description, "Moon details distinguishable only with difficulty" was right on, even through a 15x spotting scope.

Naked eye view was darker than this. A long exposure makes it brighter.

Sometimes total lunar eclipses look darker when seeing conditions are poor. But we thought Mt. Laguna had very good seeing conditions. During totality the Milky Way was easily visible along with several satellites passing by and even a couple of meteors. Mid-totality was at 7:47 and we packed up just after 8PM. End of totality was 8:23PM.

There is always hype about how rare certain astronomical events are, so I reviewed the tables of lunar eclipses to determine the rarity of this selenelion.

There are 85 total lunar eclipses in the 21st century. For each of these a selenelion is possible for 1+ time zone of longitude for both sunrise and sunset. This should cut the average probability down to less than one per decade. Nonetheless I count 9 opportunities within the continental US between 2003 and 2022, 4 of those here in the Pacific time zone. All 4 of the Pacific chances are at sunset rather than sunrise, including both 2003 eclipses.

I recall thinking about this in November 2003, but being lazy and just driving 5 miles down to Griffith Park where local astronomers set up scopes on a lawn. I remember that eclipse not being visible until it was well above the eastern horizon, no doubt aggravated by the view being over the lights of the entire LA Basin. That experience informed my excursion 3 hours from home this time.

The key factors that make selenelion viewing rare IMHO are topography and weather. Many areas including the entire LA Basin will have one of the horizons (east in our case) blocked by higher ground. Having clear weather for the last degree or so on both horizons may be even more difficult. Getting on top of the right mountain can at least double your window of opportunity. Google Earth is your friend for this research.
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"Successful Selenelion"? Was there ever a doubt that the eclipse itself would be successful? :rotfl:

Hmm, I haven't even looked at my pics on a big screen at all yet.

For the first time in days all of a sudden on Sunday we had partly cloud skies come in just as the event was starting, so we had to be flexible and drive 30 minutes or so to the NE to get enough of a view. It felt like being one of those weather chasers you see on TV. Too much going on in the short term to get to this stuff.

More interesting in my viewfinder will be the big 2017 solar eclipse which has it's centerline run through central Wyoming just a couple hours away. Probably go camping for that summertime event and hope for clear weather.
EMSC":234n0jq2 said:
More interesting in my viewfinder will be the big 2017 solar eclipse which has it's centerline run through central Wyoming just a couple hours away. Probably go camping for that summertime event and hope for clear weather.
You are very well placed for that. Interstate 25 stays close to the path for 75 miles east of Casper for ideal mobility.

Liz and I have been investigating Jackson for some time. We recently found that the head of the local astronomy club in Jackson is planning to decamp to central Wyoming ~4 hours east due to likely better weather prospects. He thinks weather forecasts a day or two ahead will be reliable. However, I'm convinced now that if you're in Jackson you need to have solid backup plan as there's probably at least a 50/50 chance you will be using it.
Tony Crocker:pext8ukj said:
You are very well placed for that. Interstate 25 stays close to the path for 75 miles east of Casper for ideal mobility.

Yeah, the mtns out this way are tall enough they tend to kick up clouds by ~11am on many many days in the summer. I suspect the Tetons may be similar.

Here are my attempts at some pics:





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I got up at 2am last Monday morning. The moon was still white, I went back to my bed :bow:

Apparently it was red later on.
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