The KBO is a small chunk of ice named 2014 MU69, at a distance of around 44 AU. We know where to find it in the sky, but we don't know its orbit precisely enough to target the spacecraft's cameras as we fly past it. Taking more images -- even with Hubble or large ground-based telescopes -- won't do the job. But hope is not lost: there are several stellar occultations, where MU69 will pass in front of a distant star, that can be used to help measure the KBO's position and size. If you set up a telescope at the right place, and observe the right star at the right time, you'll see it briefly blink out. If you do this from even a couple of different places along the shadow path, you can get a good idea of the size and position of the body.
This is relatively common thing to do for a 'large' body like Pluto. MU69 is comparably tiny -- some 10,000 times fainter -- and this makes observing an occultation a real challenge. But, New Horizons has just one chance to fly past it, so in prep for the encounter, the mission and NASA decided to invest substantial effort into a large campaign to observe three occultations with MU69 during the summer of 2017.
I was lucky enough to be invited to join about 25 others in heading to South Africa to observe the occultation on the morning of June 3, 2017 (the first of three occultations). We brought 5000 pounds of telescopes with us, primarily a dozen 16-inch motorized Dobsonians, fitted with low-noise detectors. Our plan was to fly to Cape Town, get up to speed on the equipment, and then spread apart across the occultation path, in order to observe the event on the morning of the 3rd. Another group of 25 headed to Argentina to see the same event, essentially a backup in case of bad weather at one site.
Although I've analyzed a lot of occultation data from from the ground and New Horizons, this was my first* occultation-chasing trip. This trip had a combination of professional astronomers (students, postdocs, faculty, etc.) and some very advanced amateurs, and we all learned from each other. It's an amazing world where we get to do these sorts of projects while traipsing past sage brush and springbok, and see the effects several years later in our new knowledge of the Kuiper belt.
As of early July, the data taken in June were still being analyzed. This particular occultation is a lot more complex than a Pluto occultation: smaller target, many more chords, and low SNR. [Update: Check out the NASA press release on the occultation results!]
Many thanks to the organizers for bringing me on board, and for everyone else for putting up with me sticking a camera in their face!
* I attempted to observe a Pluto occultation from Sutherland with Amanda Sickafoose, but we were blizzarded out and were eating lamb shank in town by the time of the event. And, Trina Ruhland reminded me that I observed an asteroid occultation with her and her dad -- my thesis advisor, John Bally -- at their rooftop observatory in Colorado.
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"Hey guys... can you come over here?" | |
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Well, here's something you never want to see... the primary mirror has somehow come off entirely! The scrapes on the side of the tube show that it's been bouncing around for some time. | |
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Simon gets down to assess the situation, and unscrew the mirror cell. | |
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Oh no... | |
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Amir photographs the broken connection, while Trina inspects the beautiful scenery behind her. | |
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The mirror is apparently glued into place, using a silicone adhesive. It had just a single point of attachment. | |
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Trina packs up the rest of that telescope. They won't be needing it tonight... | |
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We have 26 people on the ground. Most people are assigned to one of 12 two-person telescope teams. Aaron Resnick and I are the two 'floaters,' so our job is to fix emergencies. Time to step up to the task! Aaron gets busy in scraping out that mirror cell connection. We're going to try to reglue it. | |
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We're really lucky to get a visit by Martin Lyons, a telescope builder with one of the local clubs (the Cederberg Astronomical Observatory. We talk about mirror gluing with him. | |
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Jeff has bought some strong adhesive, and is getting ready to glue it. | |
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Glueing that mirror back on... | |
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It's very sticky adhesive -- that sort of amount will take hours to rub off of one's hands (as I found out from experience). | |
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Jeff placing that mirror. | |
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Yeah, not very flat... | |
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Martin lends a hand, and some advice. "But you know what? I don't think it's going to stick. I just don't think it will. If we had more time, what we should do is bring this telescope to my place, and I have a vacuum chamber that I use for gluing mirror cells on." | |
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Martin was right: in the morning, it was on, but not tight enough to keep it secure while rattling across dirt roads in the Karoo. |
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We're at the hotel restaurant, specializing in South Africa's favorite cuisine: red meat. Also, butternut, and beets. "Anne, certainly you'd like some of our springbok hot pot, would you not?" | |
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After dinner, we head about 300 meters down the road to SAAO. The main observatory building (with the columns) was built in 1829! There's a long history of science done here, including a lot of early work in stellar parallax. The large telescopes from Cape Town, Johannesburg, and Pretoria were moved to the new dark site in Sutherland (4 hours to the NE) in the 1970s. I suppose by setting telescopes on the observatory grounds, we are rekindling the historic age of Cape-based South African astronomy! | |
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Charles, Aaron, and Jason talk with Martin Lyons. That's the moon rising behind them. | |
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Alex aligns his finder scope. | |
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Martin Lyons proves to be extremely useful for getting these telescopes collimated. The mirrors have gotten knocked around quite a bit on their trip from Boulder, but his laser collimators do a quick job in getting the primary and secondary re-centered. | |
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DO NOT LOOK AT THE LASER BEAM!!! | |
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Eliot and Alex work their telescope. | |
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Oooh! My green laser pointer comes useful, as we try to find our target field. Our star itself is a relatively nameless 15th magnitude object, but it is near the 2nd mag star Nunki (aka Sigma Sag). One week later, my discussion with immigration in Dubai went like this: Them: Sir, is that a laser pointer you have with you? Me: Yes, it is? Them: What color is it? Me: Green. Them: Please sign this form, and we will destroy your laser pointer for you. | |
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And they are on the field! Amanda has put printed star charts in the 'Plankton,' which after some rotation eventually match what we see on the screen. | |
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Anja, Alex, and Jason try to match stars. |
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We've made it about three hours up the N7 to Clanwilliam. The city is known as a major processor of Rooibos (South African honey-bush tea). | |
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In Clanwilliam, we drop by the Yellow Aloe guest house, with the very charming Anne. | |
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"Well, but you also need good weather!", someone points out. | |
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Most of the groups searched for sites during the drive up today. On Charles' laptop are the occultation chords -- i.e., each team is assigned one line, and can put themself anywhere, as long as it's on that line (and dark, and no deadly animals, etc.). | |
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The sites along the chords are numbered from S1 to S21 (non-inclusive). 'S13' is the closest site to Clanwilliam. All the 'N' sites are in Argentina. As floaters, Aaron and I weren't assigned to a site, but will move around as needed. | |
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John Moore. | |
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Sam Strabala enjoys that tasty beverage! | |
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Our dark site near Clanwilliam is the Rondenberg Resort, which is an RV park ('caravan park') about 20 minutes outside of town. Many people stayed there, and we used it for meeting and night-time practice. Their website even has a big section covering the occultation, including articles in the Cape Times and the the local Afrikaans newspaper about the NASA group. | |
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Trina, Charles, Anne, and local SAAO postdoc Nic Erasmus, at the Rondeberg. | |
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Amir's bathroom has a tree, a climbing wall, and a stone shower. It was pretty incredible. | |
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Time to get those telescopes out! | |
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Yeah, a little bit of clouds... | |
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But we could see a lot of stars still. | |
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The night was moderately successful. A lot of equipment problems, and while we all eventually found the right field, it was slow going. The cloud coverage increased during the night, which didn't help things. You can see here too one possible alignment issue: that telescope is sitting flat on the ground, but the ground isn't flat! It was also irrigated, so things had sunk in by a few degrees at the end of the night. It's all good -- that's why we had practice nights. | |
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The telescopes need two stars to align. We'd often find one, and then it would be a long wait until a second star (bright enough, and identifiable to our hemispherically challenged minds) would come into a clear patch for long enough chase after. | |
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Not looking too good here... | |
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But hey -- at least we get a nice view of that southern Milky Way! | |
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By 3:30 AM it still wasn't clear, but we'd gotten aligned a few times, found the field twice, and basically knew what we were doing. | |
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Whoa! And by 4:30 AM it's cleared up, and here's our star field! Sagittarius is easy to see. We aligned on the 2nd mag star Nunki, and then it's a small offset from there to MU69. Pluto and Saturn are nearby. That's the Small Magellanic Cloud at the lower left, and someone's body at the lower right. | |
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At lunch the next day, Jeff and Simon scheme. | |
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While Emily plans back at the guest house. | |
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Jason Mackie is a man of many careers, including a long stint building store fixtures for shopping malls. But now, a chance meeting has gotten him into occultations... this is is second, after a Pluto occultation in New Zealand in 2015. | |
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Oh, what I woud do to have the title Grant Spammer, Amagqwetha. | |
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Ted Blank. | |
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Time for a group meeting! The weather is not looking very promising. We have 36 hours until the event, and the prediction for Clanwilliam is pretty patchy. By this time of year usually it is raining, so we're better than normal, but not quite good enough. We have a long discussion, and eventually decide that half the groups will stay in Clanwilliam, and half will head east. Far enough easy, and the weather is predicted to be clear. | |
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Just how far are we going? About 600 km, past Carnarvon, to Victoria West / Vosburg. This is solidly in the middle of the Karoo, in a very remote area of the country. | |
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As our chief predict planner, Simon stays at the Clanwilliam so he can be in touch with the Argentina team. | |
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RJ maps out his destination. | |
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John Wilson is among those of us who love oranges. | |
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Jason likes cats, and they like him (or at least his meaty sandwich). | |
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A challenge to the reader: find all ten cats in this picture. Hint: they are all in a line. | |
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Christian reads out everyone's new assignments! | |
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Con gets ready to drive: gas up, and buy those jerry cans! | |
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Meanwhile, videographer Alistair Daynes has joined us in Clanwilliam. He and Sam Chevallier are Capetonians who have been enlisted to work on the project with Geoff Hanes-Stiles and APL, who are doing documentary of the NH extended mission, including the MU69 occultations. |
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We meet back up with Ted and Paul. They've been out scouting as well, and have found a great location for their telescope. They'll set up on an ostrich farm, next to a small church as a windblock. | |
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Eugene gets that braai going. How long does it take? "If you want to do it right -- seven hours." We've got about three -- so we talk him into the express version. | |
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Even standing right in front of the braai, it's cold! | |
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Time to toss on that meat! We have some boerewors, some beef *, and some chicken. "Look, you need to know the rules of braai. The first rule of braai is: you don't have vegetable. You want a vegetable? Have a chicken." *In Mumbai where we live, 'beef' is listed on menus occasionally. But what they mean by that is almost always water buffalo. | |
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Charl gets those boerewors going. | |
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Around 12:30 AM, we packed up and headed out to the ostrich farm with Ted and Paul. Their site was pretty close to the centerline -- meaning that if someone needed floater assistance from us, we'd be in a good spot to go help them out. Nic helps Ted and Paul set up that Dob. These were relatively inexpensive telescopes (about $3500 each), but worked pretty well. They are full GOTO systems -- that is, they have two motors and a handpaddle, so you just enter the coordinates and the scope will slew, and then track as the Earth rotates. In the past, portable occultations have been done a lot with large Celestron / Meade SCT's. For comparison, a 16" Meade SCT runs $16,000, and weighs 318 lbs uncrated. The relatively low weight and cost of these scopes made this trip a lot easier than it would be otherwise. A 16" telescope is big enough to get enough signal:noise on our 15th mag target star, but anything less would be insufficient. | |
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Ted pulls up the secondary, and mounts the camera in the eyepice tube. We're using a low noise CCD from QHY. | |
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Now it's time to collimate: set the mirrors so they are aligned with each other. The laser beam makes that easy. | |
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And we're set up and aligned on the sky! It's about 2 AM now, and we have about 2.5 hours until the start of the event. A risk of setting up early is that the optics will cool down, and you'll get condensation on the mirror -- something we definitely don't want. So we lay a tarp over the telescope, to keep it covered. | |
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And there's the beautiful southern sky! The Milky Way is running top-to-bottom, and the two clouds to the left are, appropriately, the Small and Large Magellanic clouds. The faint green banding is real: that's airglow of oxygen at 557 nm -- in a way, a very low-level aurora generated in the Earth's upper atmosphere. The glow silhouetting the mountain is from another city maybe 15 km to the south. | |
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Here's Nic, Jason, Aaron, and Ted. Aaron managed to keep his arm pointed at the Milky Way for the entire 178 seconds! The south celestial pole is obvious -- it's where the star trails turn into static points, a bit left of the center. NB: NASA picked up this photo and for a few weeks used it as the NASA banner photo on their Facebook account, with 6000+ likes. Awesome! (As of today, they've changed it to shot of the ISS + American flag.) What I love about this shot is that while it is 'posed' (in the sense that I told them to hold still!), we're really out there doing science, and this is really what we get to do, and it's great. | |
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An hour to go before the start time, and we get a message: FLOATER NEEDED NOW! Aaron and Jason hop in the bakkie, and take off. Those are their headlamps as they went on either side of me. | |
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We're getting read for the event, with just a few minutes to go. Ted preps the laptop to acquire data. The occultation proper is three seconds long, but we (and the other teams) will be recording data for a full 45 minutes. This is a good idea for a few reasons, among them being that if MU69 is surrounded by a (very) dense ring system, this might give us some chance at seeing it in occultation. | |
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On the target. | |
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That's our target field! | |
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The wind has been going in and out, with some small gusts at times. One disadvantage that these small telescopes have is that they're really easy to blow around in the wind. If we get a gust at the wrong time, it won't blow us off the field, but it will certainly blur the stars. To minimize wind, we've set up close to the building (it's a church), and we've pulled in the bakkies close. Then, for the 45 minutes of the obsevation, we'll take turns holding up a wind tarp in front of the telescope as well. Pretty soon we'll kill all the red headlamps, and cover the laptop screen, to avoid any stray light hitting the telescope. The observation started a few minutes later, and I didn't dare take any photos during that period -- I'd be likely to trip on a cable or fire off a flash. | |
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And... occultation complete! We recorded a full 5400 frames at 2 Hz. Ted and Paul have turned back on their lights, and are backing up the data from the laptop to an external drive. NASA also used this shot for a press release... it's definitely one of my favorites. | |
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And we've moved off the field! It's a clear, still, and moonless night, and we have a great telescope and some huge skies, so let's go observing! We're on the Magellanic Clouds now. Saturn was huge and beautiful. We saw Venus as it was rising, as low as it possibly could be -- probably half a degree from the horizon, and going through a crazy rainbow of colors. (And we knew from experience that if that primary mirror hadn't fallen out yet, it was glued in solidly enough that tilting it to the horizon wasn't an issue...). It's rare to see Mercury, but here, it was bright and easy, about 5 degrees up. Our security group -- all four of them -- got a kick out of seeing everything... they've worked with a lot of groups before, but never astronomers. | |
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And here are where all the teams ended up. We found great sites, and the weather more-or-less held in Clanwilliam, so every team ended up getting usable data. |
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We're flying out in the evening, but with the telescopes off, we have most of the day free around Cape Town. Five of us gather at 6 AM for a hike up Table Mountain. | |
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No stargazing allowed! We're headed up the Platteklip Gorge trail, which starts just past the cableway, and ends on top (obviously). | |
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Christian and Charles have set a pretty bruising pace on the way up! This route is 2 km, but with 0.8 km of vertical elevation gain! Looks like Charles is photographing a protea, which is the South African national flower. An amazing fact I read: there is a greater number of plant species on Table Mountain, than in all of the UK. It could well be true: Table Mountain tops out at 1100 meters, which is only slightly lower than the 1300 meters of Ben Nevis, the UK's highest point. | |
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Go go go! | |
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Trina was patient with all of us, even feeding me some tasty blueberry bars. I should have done more to slow her down. Trina: "Dude, you didn't bring your camera?!?" Me: "That thing is so heavy!" Trina: "I totally would have carried it for you!!" | |
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NB: Table Mountain is a UNESCO site, and one of the most visited places in the country. I'd been up before, but only on the cableway -- not the trail. The trail was steep, but it was dry and cool, and really beautiful. It took a bit over an hour to get on top. | |
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Nearing the top... | |
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Hey, we're 3/4 of a mile higher than the airport... | |
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On top! Trina walks along a path filled with... frogs. Everywhere, we heard the noise of little tiny frogs talking to each other. It was amazing and totally unexpected. Was it related to the fact that it had rained two days earlier, breaking the drought? Someone knows, but not me! | |
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Last time I was on Table Mountain, it was a white-out, with visibility of not much more than few meters. Also beautiful, but it was great to be able to see the whole surface. It's really surreal. On the horizon behind us is the real summit (which is on the far end from the cableway). We've almost made it out there. The round trip on top added 2 or 3 km to our escapade. | |
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For a few brief seconds, Trina no doubt has the highest feet in Cape Town. | |
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Behind us is 'Maclear's Beacon' -- the true high point (16 meters higher than the other end of the plateau!) | |
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This is cool: "His tribute to this mountain was his naming of Mons Mensa (Latin for Table Mountain) -- the only constellation named after a geographical feature in the world." | |
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Just about to head down the cableway. You can see the 2010 World Cup soccer stadium just below to the left. | |
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Have to talk to the rock hyraxes ('dassies') first! A cute little animal, whose closest relative is the elephant. | |
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And in the cablecar... 6 minutes and we're down. | |
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In the evening I head back to India. En route I have a layover in Dubai, and meet up with a friend there. | |
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John and I go out and look for camels. | |
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And we have a great drive through some local sand dunes outside of town. We took a little walk through the dunes (114 degrees!), and for safety, we left the car running, so the motor wouldn't get stuck. When we came back the motor was still running. But try as we could, the wheels were stuck in the sand. (And yes, we did try... getting them more and more stuck every time.) | |
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Eventually, we called for professional assistance. | |
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Where are we? Kind of near a road that's buried, and in the middle of a bunch of sand dunes? The closest business to us was a place called Camelicious. Apparently it's a camel milk processing factory. It's 10 km away. | |
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Our towtruck driver showed up with a heavy flatbed, which he left behind even before all four wheels were on the sand. It was hopeless for him to drive out to us. We walked the kilometer to our stuck vehicle. He gave it a valiant effort, before advising us to abandon it for the night, and walk back. And he did this sans water -- it's Ramadan. All ends well: a bit of a tow from another 4WD and it was freed the next morning. |
Last modified Sun Jun 11 01:41:41 2023