Wednesday 7 September 2011

*** JWST - to be or not to be??****

James Webb Space Telescope (not yet in existence!) The weird looking structure under the main mirror is a shield to keep heat from the Sun away from the telescope.

JWST vs. HST mirror size

The JWST is billed as the "next big thing" in observational astronomy after Hubble. Because of massive cost overruns and mismanagement, JWST is threatened with cancellation by Congress. Several billion dollars (thats billion with a "b") have already been spent on the project, and the total cost estimate keeps rising- its now up to ~$9 billion. JWST is not "too big to fail". In the 1990s, Congress canceled a massive physics project , the SSC (superconducting supercollider) after billions had been spent because of the same sorts of problems that beset JWST. (There is a tunnel 14 miles long under Texas that was dug to house part of the SSC!!)

Should you care?? Well, if you are going to become a research astronomer, the JWST will be (might have been?) one of the most important astronomical instruments of the 2020s and 2030s, just when your career would be in full swing.

What is going to happen? I don't know. Many astronomers are questioning whether it is good to spend so much money on one project. If Congress won't give NASA more money for JWST, NASA may decide to raid other projects for the cash to finish JWST. Needless to say, the folks running the other projects will fight tooth and nail to keep their projects alive. This promises to be a nasty astropolitics fight.

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***Weightlessness or "Help I'm fallllllllllllllllllliiin.....****

I am sure you have all seen videos of astronauts "floating" around inside the Space Shuttle or Space Station. In these orbiting environments, objects are weightless. Things "float" around , liquids form spheres etc etc. What is going on??

The astronauts are certainly NOT, as many people believe, "beyond Earth's gravity". In fact, at the altitude of the Shuttle (typically 400 km above Earth), the Earths gravitational force *is* lower than on the surface, because the Shuttle is farther from the center of the Earth than is the surface. But the force at Shuttle distance is about (6400*6400)/[(6400+400)*(6400+400)]= 0.9 times that at the surface. So the gravitational force at Shuttle altitude is just 10% lower than the force at the surface! If you were standing on a 400 km high mountain, you would weigh 90% of what you weigh at sea level. (There is no such mountain, of course. Everest is about 9 km above sea level).

The astronauts are weightless BECAUSE THEY ARE FALLING. When you fall, you are acted upon ONLY BY THE FORCE OF GRAVITY. Normally, as we stand or sit, we are not moving or accelerating relative to the Earth. Thus, by F=ma, we are experiencing no *NET* force, as a=0 so F must be 0. HOWEVER, we are ALWAYS acted upon by the force of gravity. Whatever is supporting us (ground, chair, bed) exerts an equal and opposite force to counteract gravity, so the net force is 0. It is this upwards force that we interpret as weight. If you are falling, there is no force counteracting gravity (well, if you are falling in the atmosphere there is a force of air resistance, but at low speeds that is not important). When you are falling there is no upwards force, so no weight!

Here are just a few pictures of people in weightlessness.

Weightless in C131 aircraft In an aircraft, you can get 20 or 30 seconds of weightlessness at a stretch by climbing and then diving. (The time is limited by the requirement that you pull out of the dive before the airplane trajectory intersects the ground. As they say, there are Old pilots, and there are Bold pilots, but there are no Old Bold pilots.) Here are two Mercury astronauts (back in the 1960s) training in a weightless aircraft. Such an aircraft is universally called a "vomit comet" as people have a tendecy to lose their lunch in weightlessness.

Bad hair day? Here is a astronaut in the space station.

Free fall Again, some astronauts in the space station. In weightless conditions, "up" and "down" and "floor" and "ceiling" lose their meanings!

***Eclipses***

***NEVER, NEVER, NEVER, NEVER look at the Sun without proper filters! You can look at the **TOTALLY ECLIPSED** Sun with your naked eye, but if even a small bit of the bright part of the Sun (the photosphere) is uncovered, DO NOT LOOK AT IT. You risk permanent eye damage. ***

Shadow shape. Because the Sun is not a point of light, but is extended, the shapes of the shadows cast by bodies like the Earth and Moon are quite complicated. There is a "dark shadow" (umbral shadow) and a "lighter shadow" (penumbral shadow). Think about what you would see if you were located at the various places A,B,C,D,E. (Position A is in the "dark cone" (umbral shadow)).

Lunar and solar eclipses. This shows how the Earth, Moon and Sun are lined up to produce a lunar or a solar eclipse.

Eclipses and line of nodes. Eclipses do not occur every month, as you might expect, because the plane of the moons orbit around the Earth is tilted slightly from the plane of the Earths orbit around the Sun.

Eclipse travel advertisement. Some people spend lots of $$$ and time to travel to the ends of the Earth to see total solar eclipses. If you have the Big Bucks you fly your private jet along the eclipse path, avoiding possibility of clouds interfering with your view.

Solar eclipses worldwide 2001-2020. Just in case you need to make travel plans. Actually, there are not that many good total solar eclipses in next 10 years. The next *total* solar eclipse will be 13 Nov 2012. The eclipse path crosses a piece of Australia but is mostly over the South Pacific where there is little land (better put down a deposit on that Lear jet rental now!).

There will be two solar eclipses visible from the US this decade- an annular eclipse in 2012 and a total eclipse in 2017.

***********The next few slides are images of SOLAR eclipses*********

May94 annular solar eclipse. This annular solar eclipse was visible from Oklahoma.

Beginning of solar eclipse. Here the Moon has just started to cover up the Sun in the beginning phases of a solar eclipse.

Total phase of solar eclipse. When the Moon totally blocks the bright disk of the Sun, we have a "total solar eclipse". During a total solar eclipse, we can easily see the faint outer part of the Sun, the corona, which is usually not visible because it is completely overpowered by the bright solar disk.

Multiple exposure view of solar eclipse This shows a complete solar eclipse as a multiple exposure. The exposures were taken over a period of time of a few hours and go from time Moon takes first "bite" out of Sun, through totality (middle of sequence) to last "bite" out of Sun.

Annular solar eclipse When the Moon is too far from Earth to completely cover the Sun's bright disk, a ring or annulus of sunlight can be seen. This is called an annular solar eclipse.

Solar eclipse from Earth orbit This image, taken from the Russian space station Mir in 1999, shows the Moon's shadow on the Earth during a solar eclipse. Compare this to the diagram of a solar exclipse of 24 January "Solar and Lunar Eclipses".

Some nice images of the July 2010 total solar eclipse that passed over Easter Island and South America:

Easter Island eclipse

Eclipse and Moai The Moai are the famous stone statues of Easter Island.

Eclipse at sunset over Argentina

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Total solar eclipse 1970 The blue line outlines the path of totality for this 1970 total solar eclipse. I saw this from Georgia when I was in high school. The corona was absolutely astounding- it looked like someone had vaporized pearls and spread them around the Sun! If you ever get a chance to see a total solar eclipse, JUST DO IT! (Annular eclipses are nice, but you don't get to see the corona- even a small slice of the bright part of the Sun is enough to overwhelm the corona.)

*******The next few slides are of images of LUNAR eclipses********

Beginning of umbral lunar eclipse Here the Moon is entering the Earths dark shadow (the umbra).

Total phase of lunar eclipse Here the Moon is totally within the Earth's umbral shadow, and we have the total phase of a lunar eclipse. The Moon looks much fainter than usual, because direct sunlight is blocked by the Earth. There is some red light that is scattered by the Earth;s atmosphere which illuminates the Moon, giving an eerie reddish or coppery color to the Moon.

Mutiple exposure view lunar eclipse over Maui Looks like a nice place to see an eclipse from!

December 21 , 2010 Lunar Eclipse Hope some of you saw this back just before Christmas 2010. It was a very nice eclipse, with the Moon very high in sky as seen from Oklahoma.

Fantastic lunar eclipse montage. Wow. A stunning montage image of a lunar eclipse- you can clearly see the size of the Earth' shadow.

December 2011 lunar eclipse We will see the eclipse as Moon is setting, thus right before sunrise. Dress warmly!