Astro 28N: Field Astronomy from the California Mountains: Observing an Asteroid Occultation

May 13-15, 2005

Post-Trip Highlights!

Check the May 3 update below! Important change of location...

Our Astro 28J class to the Southern Sierra was such a great success in such a beautiful spot that I'm looking forward to having another trip to this area. Check out the many great pictures from this trip here. The final location will depend on a final updated path for the main astronomical feature of this weekend - the occultation of a star by the asteroid Io. This is a main belt asteroid with a solid orbit determination, and the star also has a precise position measured so I don't expect much of a path shift. We'll likely want to have our camp at Sequoia National Monument again. And of course, you can expect my usual fine dining - french crepes breakfast and dinners of basmatti rice and fresh vege wraps, all enjoyed around a campfire while I lecture on the moon, stars, nebulae and galaxies of the spring sky.

The Setting

Giant Sequoia National Monument is one of the new national monuments created in the '90's, created to protect some of the last habitat of the largest trees on earth - the giant sequoia. The area also shows dramatic examples of the mountain building processes which formed the surface of our and the other inner planets since the Sierra is a very young mountain range. We'll have panoramic views of the Kern River canyon, granite domes shaped by the last ice age, and crystal clear dark skies to study the great galaxy clusters of Virgo and Coma Berenices in the spring sky.

During the day, we'll explore Trail of 100 Giants at the Long Grove of giant sequoias, go to Dome Rock to view a hundred square miles of southern Sierra terrain and hear my lecture on planetary crustal processes, explore green meadows, and on the way home perhaps visit a hot spring on the lower Kern River, or stop at California Hot Springs - an unpretentious little resort from the old days on the windy drive up to our camp.

The Asteroid Occultation

The asteroid Io will occult a star of visual magnitude 10.6 on Saturday evening May 15 at 8:55pm, just as twilight is ending. As the asteroid moves through space, its shadow will trace a band 200 miles wide across central and southern California. Steve Preston prepared a special prediction run for us. The path of the event is given in table form here. Our goal is to be inside this path so we can see the star wink out as the fainter asteroid passes in front of it. The star's a red giant. That's good! Our PC164c digital camera is most sensitive to red light and this should be easy to record on our equipment. I'll be able to record and play back on a portable TV/VCR system the event for us to study. We should have 2 or maybe 3 stations which we can set up in different locations to help determine the size and shape of this asteroid - a subject of intense scientific interest in recent years. The current best estimate of the path for this event is shown here. Click on it for a larger view.

Here's an interesting page on asteroid occultations. And here's a video recording of a bright asteroid occultation.



Asteroid occultation math whiz Steve Preston's updated path at left is more accurate. A possibly important thing to note is that there have been 2 occultations by Io observered recently, and both gave a north shift of about 1/3 path width. If this is due to inaccuracies in the asteroid orbit (as opposed to star position errors), then the path at left should perhaps be shifted north by 1/3 width. This would put Sequoia National Monument inside the northern limit. Either way, it looks likely that astronomers from the Southern California area may have the central and southern part of the path well covered, so we our position near the northern limit is good bracketing for the ultimate goal - a well-covered path from everywhere inside the 1-sigma limits.

Click here to see a video .mpg of a bright asteroid occultation recently recorded in Texas.

Registering for the class...

The initial sign-up day, Feb 9, is now past. However, there are still open spaces for this class. We have 21 students so far, and have space for 7 more. Call me (479-6506) or email me. There is a $15 camping fee, and upon receipt of the fee, I will have our division personnel approve your name in the Admin&Records computer to allow you to register for the class. I'm easiest to reach if you come by my office at 706a at 11am sharp on Monday or Wednesday.

There is, as always, an on-campus session before the trip. It's on Wednesday afternoon May 4 at 5pm in Room 706 - the Cabrillo College Planetarium. At this session we'll arrange car pools, distribute maps and detailed instructions. I'll also have a lecture and planetarium show with slides. I love cooking great meals for my classes, but new rules imposed by state codes, forbids me to buy your food. So, I'll have a list of the ingredients, and we'll find volunteers or perhaps a single 'shopping czar' to buy what we'll need.Note that the on-campus first meeting of the class is one week before the date in the schedule of classes. This is by universal agreement at the sign-up session. It will be good to have an extra week for students to get together to buy the food.

Update Mar 19

I've received a nice honor - I've been invited to be one of the grand award judges in the International Intel Science and Engineering Competition. This is a big deal, with the best high school science students in the world doing projects competing for millions in scholarships. This year, it's being held in Phoenix, Arizona the week before our trip. I must be in Phoenix all day Tuesday and Wednesday. I've decided it makes the most sense for me (given my bad hip) to drive there, and then to drive straight to our camp afterwards. Might take a bit more logistical planning. Stay tuned...

Update May 3

A heavy winter, late storms, and cooler than usual weather has kept snow on the ground in the Sequoias and all the campgrounds in this area are closed until Memorial Day. I've tried to find alternative campsites that would allow visiting the sequoias and also see the asteroid occultation, but no luck. So - for the second time in the history of Astro 28 - we're moving the location. The new location is the southern Big Sur mountains. There's a beautiful campground on the Naciemento River called Ponderosa Campground. The west fork of the Naciemento River winds through a meadow below some astro-friendly camp sites which face south looking towards the spine of the Big Sur Mountains. A short drive through forests of maple and steep canyons will get us to the pass at the top of Naciemento-Ferguson Road with a dramatic overlook of the Big Sur coastline. During the day we'll explore the complex geologic history of the Big Sur as told by the rocks and minerals we'll explore along the beaches. Kirk Creek has an especially scenic and dramatic coastal access. Later in the afternoon you'll have some free time to enjoy other spots - 5,000 foot Cone Peak, Sand Dollar beach, one of the most beautiful of the original California missions - Mission San Antonio, and wildflowers fields that surround it.

The good news is - this location is deeper inside the predicted asteroid occultation path. The Sequoia location was a little north of the predicted northern limit, while Ponderosa Campground is south of the northern limit and has a better chance of getting the event. The southern limit goes through L.A. where there are other observers so with a little luck we should be able to help map out this asteroid. Io has had two other asteroid occultations successfully observed, so if we're lucky this time, we'll be contributing to the data which will allow a 3-dimensional reconstruction of the size and shape of the asteroid - all without a 5 bazillion dollar spacecraft flyby!

I'll have maps, and other handouts at the pre-trip meeting which is May 4 at 5pm in the planetarium.

PostTrip... Another great trip filled with astronomy, geology, and adventures. Check out the Post Trip Highlights page with all the photos. It's a work in progress at this point.