Monday, February 7, 2011

My Review of Red LED with Holder (2-Pack)

Originally submitted at RadioShack

Use with digital clocks and remotes. Typical MCD is 0.8. This Red LED has a typical wavelength of 655nm.

Good for on-off indicator

By Beachastro from Hampton, New Hampshire on 2/7/2011


4out of 5

Pros: Pkg instr actually clear

Cons: Hole dia not specified

Best Uses: On off ind

Describe Yourself: Enthusiast

Primary use: Personal

Was this a gift?: No

Pkg reads: Power diss. 110 mW, Fwd. current: 40mA
Fwd voltage: 1.7V at 20mA
Luminous intensity: 0.8mcd at 10mA
Long lead is anode (+) connection

Unlike many of the other packages, this one had enough info to actually calculate the resistor required! Since my power supply was 12V I ended up using 2.2K ohms to get the dimmest light I could. A 1K resistor was just too bright, this will be used outdoors while observing with a telescope so dim is better. BTW, correct hole size is 15/64". :-)


Sunday, December 5, 2010

Measuring the size of an asteroid

Asteroids are small and dim, but over time astronomers have managed to calculate the orbits of thousands of them. What is less well known, however, is their size and shape. They are just too far away for even the largest telescopes to get a good picture of any but the very largest ones.

However, once in a while, an asteroid will pass directly in front of a star (as visible from Earth) and for a brief few seconds the star will wink out, then reappear as it emerges from its eclipse. An event like this is called an "occultation" (because the asteroid temporarily occults, or blocks, the light from the star).

Timing the length of the occultation to a fraction of a second can actually give us an estimate of the size of the asteroid. Since we know its orbit and speed, knowing how long it occults a star makes it easy to calculate its size.

But what if the asteroid is oddly shaped, like say a peanut? Then an observer on earth who saw the fat part of the peanut occult the star might measure the star winking out for say 10 seconds, while an observer on earth a small distance away might see the star wink out for only 6 seconds, depending on whether the fat or the skinny part of the asteroid passed between their eye and the star. But if there were many observers, and they each had accurate clocks, you could actually use these observations to sketch an outline of the asteroid!

This is exactly what the members of the International Occultation Timing Association (known as IOTA) do. They coordinate their locations across the path of the asteroid's shadow on earth as well as along its "ground track" and send their data to the organizations central database. Over time, these observations build up and provide information about these objects size and shape. In addition, the actual times of arrival of the shadows lets astronomers improve their estimates of the orbit of the asteroid. All of this knowledge from a few frames on a video camera where a star disappears!

Well, this morning I made an attempt to add to this database by observing and recording the occultation of star TYC 5559-00693-1 (a very dim, 10th magnitude star) by the asteroid Hygiea from Hamton Beach State Park. This asteroid is pretty big, about 470 km across, so the occultation was expected to last about 10 seconds or so and cover a wide swath of ground across the Northeast. The occultation was scheduled to happen at 5:07am, so I set up my equipment (telescope and video camera) at 4am to record the event.

However, as I zoomed in on the area of the star that was going to be occulted, all the stars around it matched up with my sky map of the area except one. There was an extra, dim star very close to the target star, and this dim star did not appear on the star map. For a moment I wondered if I had mistakenly pointed my telescope at the wrong area of the sky. Then I realized with a rush of excitement that this "extra" star was actually the asteroid itself, on its way to pass in front of the target star. I actually saw the asteroid and the star close to each other!

Although I was now sure I had the target star clearly identified in my eyepiece, unfortunately a bank of clouds rolled in at 4:30 and by 5:00am not even bright Venus could be seen in the sky. Such is astronomy in the Northeast. So I hope my fellow IOTA enthusiasts who were spread out across Massachusetts and Connecticut had clearer skies.

There are hundreds of occultations each year, so I will try again soon.

Friday, September 3, 2010

Jupiter takes over from Saturn

It's with some sadness that we bid Saturn a temporary farewell in the evening sky. Earth's progress in its orbit has brought us around to the side of the Sun where Jupiter is currently travelling, leaving Saturn too low in the west to see it from the East coast. Interestingly, I just got back from a trip to California and out on the West coast Saturn is still high enough after sunset to get about an hour of viewing. We'll give Saturn a well-deserved rest, and when we see it next year those rings will be opened up a few more degrees and the view will be even better.

Meanwhile Jupiter has begun to dominate the evening sky, and in the past week literally hundreds of people have seen it (and its moons) from my usual outpost on the sidewalk in Hampton Beach. This has been one of the clearest weeks in recent memory, and the first time I can remember doing sidewalk astronomy four nights in a row without any interruption for cloudy weather.

We also had a few nights where the waning gibbous moon rose early enough for some clear views.
I have started handing out 4x6 cards with some lists of local astronomy resources (club web sites, web sites for Stellarium and Cloudy Nights, etc.). On the back I put a reproduction of the page of Galileo's notebook in which he made the first sketches of Jupiter's moons in 1609/10. I may have to raise my estimates of how many people looked through the telescope, last night I gave out 30 of these cards in 2 hours, and that was mostly to kids. I think I have been underestimating how many people look through the scope, but I guess I'm having too much fun talking to people to count them!

Monday, March 8, 2010

Teaching depends on what other people think

An article in last Sunday's New York Times magazine about teaching how to teach contained this quote:

"Teaching depends on what other people think, not what you think."

The author of that quote was Deborah Ball, Dean of the School of Education at the University of Michigan.

I like teaching. Right now I mostly teach Astronomy. I don't claim any special knowlege of the subject over what an interested amateur can aquire in a few years of reading and observing.

I do, however, feel that I have a sense of what my students are thinking, what their mistakes are, how they make them, and how to lead them back to a proper understanding of a subject. Deborah Ball calls this the ability to step outside of your own head.

For me, it involves trying to have a trick, explanation, demonstration or other technique for correcting "wrong thinking" in a way that illuminates the problem and shows why another approach gives better results.

So preparing to teach Astronomy has required learning at two levels. First were the facts and theories themselves. Then came learning how to teach these concepts in ways that were fun, entertaining, and above all "sticky." Some of these techniques I have gotten from books, some from other Astronomy Club members, and some have been born of necessity during that moment of inspiration in front of a group when nothing you have tried has worked and you really need a new approach.

I find the development of the skills to teach the subject as much fun as I have found learning the subject itself. Actually teaching it - where the skills and knowledge come together in real time to make that "aha" moment for people - is more enjoyable still.

I feel I have always been sensitive - some have said perhaps too sensitive - to what other people think. Is it possible that this is a trait which might contribute to success in teaching?

Busy couple of weeks!

The last few weeks have been filled with wonderful activities and fun events. Members of my astronomy club, the New Hampshire Astronomical Society, joined me for an evening of sidewalk astronomy in Portsmouth. We had a wonderful time, lots of visitors of all ages. Mars, M42, the Pleiades, and first quarter moon all competed for attention. Then I gave a talk at the Rey Center in Waterville Valley, NH. Margaret and H.A. Rey were lifelong residents of Waterville Valley. Among their many accomplishments were the Curious George series of books, and a book called "The Stars - A New Way to See Them" in which they drew new outlines for the same starts in the constellations to form figures which matched their names more closely.

One of the demonstrations in that book included an umbrella to show why the Big Dipper appears in different orientations (sometimes holding water, sometimes on end, sometimes pouring water out onto the ground) at different seasons of the year. Several years ago I made one of these out of a large clear umbrella and I have used it in many classes. It was a real honor to "bring it home" to the Rey Center and use it in a demonstration where the Reys lived and worked.

NHAS sponsored a skywatch for the Alton School in Alton, NH. I spoke there on the life cycle of stars and various "What's Up Tonight" topics, then we all went outside for a few hours of observing. Some clouds marred the sky for the first hour, but then things cleared up and it was glorious for a couple more hours.

Finally, last night a friend and I spent a relaxing few hours in Portsmouth showing people Mars, M42 and eventually Saturn once it rose over a building. I put some stickers on the curb at the right distances for the planets and invited people to walk down Congress St. on the "Portsmouth Planet Walk" to see the relative distances of the planets. One mom responded, "Oh we know all about that. We parked near Jupiter!"

Thursday, February 4, 2010

First light with XT10i

I picked up a used XT10i from a friend, and it is giving excellent views.

For the first time I was able to see surfact markings on Mars, at about 10:30 pm when Mars was nice and high. A 9mm EP with 2X Barlow gave 266X.

This morning I enjoyed views of Saturn (4 moons clearly visible, but rings are closing...sad). Also nice views of the moon at 3rd quartet. Lots of detail visible including lava flows along the floors of the plains.


Wednesday, January 13, 2010

Sidewalk Astronomy - Early Evening Jupiter

It's been clear and cold in the Northeast lately, so with some warm boots, long underwear and assorted

hand and head coverings I set up on the Portsmouth sidewalk in front of Starbucks for a couple of hours each evening for the past few nights.

Amazingly, it seemed like more people were interested in viewing through the scope than is typically the case in summer - almost 100% of people said sure and enjoyed the views. We looked at Jupiter on nights when I was out early, and Mars and the Pleiades for later events after Jupiter had set. I also took a peek at M42 when nobody was around, but due to the light-polluted sky it was less than impressive.

One of the Portsmouth parking meter readers (yes, the ones who give tickets) thanked me for giving back to the community, he has seen me many times in various spots around town. Jupiter's 4 moons were clearly visible, as was the jet stream blowing past the planet. Cloud bands were vaguely visible at moments when seeing steadied, but these moments were few and far between.

One other thing - it's exactly 400 years ago this week that Galileo recorded sketches of Jupiter's moons in his notebook, later publicized in his "Starry Messenger".