Dear Friends,
Here is the next in my occasional series of space science updates, with info today on the May 4 lunar eclipse, observing Venus, the Venus transit, and the latest NASA space science missions. instructions for subscribing or unsubscribing can be found at the end of the message.
Best wishes,
Jeff
1. LUNAR ECLIPSE MAY 4
There is a total eclipse of the Moon tomorrow night (May 4). Those of you in Europe, Africa, and Australia can watch it. It will not be visible in North America, but you can still watch it on the web at http://www.xs4all.nl/~carlkop/eclipsmaan/leclips2004.html.
2. VENUS AT ITS BRIGHTEST THIS WEEK
Venus has been incredibly bright in our skies for more than a month now, but is only just now reaching its peak brightness. Be sure to have a look at Venus in the evening skies this week — just look to the west after sunset, and you can’t miss it if the sky is clear. NASA science news has posted a great article about why Venus is so bright right now, and how it is often mistaken for a UFO.
Questions you might want to ask your students in class:
- Venus is very bright right now in part because it is at a point in its orbit where it is fairly close to Earth. However, once it reaches the point where it is CLOSEST to Earth, we will not be able to see it at all in our sky. Why not? (Answer: At its closest, Venus lies between the Sun and us, and therefore it is completely obscured by the light of the Sun in our daytime sky. In addition, even if we could see it at this time, we’d be looking only at its night side ("new Venus").)
- Look at Venus through a pair of binoculars (be sure to hold them steady on a tripod). You’ll notice that we do not see a "full Venus," but rather see a phase of Venus much like a phase of the Moon. What phase do you see for Venus right now? (Answer: crescent.)
- Do we ever see a full Venus? Why or why not? (Answer: No. Venus is "full" when it is on the other side of the Sun from us — which means that we cannot see it because it is in the same place in our sky as our Sun and therefore drowned out by the light of the Sun.)
- The Moon is much brighter when it is gibbous (almost full) than when it is a crescent, but Venus is the opposite: brighter when it is a crescent than when it is gibbous. Why? (Answer: If you draw a diagram showing where Venus’s phases occur in its orbit [as seen from Earth], you’ll see that Venus is much farther away from us and hence dimmer when it is gibbous than when it is a crescent. In contrast, the distance to the Moon does not depend on its phase, so it is brighter when a larger portion of its visible face is sunlit. Note: NASA has a nice applet explaining the phases of Venus.
3. TRANSIT OF VENUS
As Venus continues along its orbit, in a few weeks it will reach the point where it lies between the Sun and Earth. This year, however, something special is going to happen at this point. The plane of Venus’s orbit around the Sun is not quite perfectly aligned with the plane of Earth’s orbit around the Sun (the ecliptic plane). As a result, when Venus passes between us and the Sun, it usually passes a little above or below the Sun in our sky. About twice a century, however, Venus passes right across the face of the Sun in what we call a transit. The last transit of Venus occurred in 1882, some 122 years ago, and careful observations of it helped astronomers pin down the true scale of the solar system. The next transit of Venus is coming up on June 8. Lots of great information about the transit, including how to observe it either yourself or on the web, can be found at http://www.vt-2004.org/index.html. (For a quick primer, check out their teacher’s guide.)
Questions for class:
- Suppose that Venus DID orbit the Sun in the same plane as Earth. How often would we have transits in that case? (Answer: every time Venus passes between the Sun and Earth in its orbit, which is about every 19 months).
- What is Venus’s phase during a transit? (Answer: new.)
4. PUTTING EINSTEIN TO THE TEST
On April 20, 2004 NASA launched a new satellite dedicated to testing Einstein’s general theory of relativity with unprecedented precision. The satellite, named "Gravity Probe B" (also the winner of this year’s award for "most creative satellite name — NOT") is in some sense the longest running NASA mission ever, since work on its development began more than 40 years ago. The long lag in getting to launch had to do largely with the extreme technological requirements of testing very subtle effects predicted by Einstein’s theory. The lag also led to the mission becoming embroiled in controversy, as some scientists argued that the effects it was designed to test have already been tested and confirmed in other ways by now, and therefore that this additional test was not worth the huge expense of a space mission. The controversy is moot at this point, since the satellite is now in space. Read more about its mission.
5. KEEPING UP WITH MARS AND SATURN
The two rovers Spirit and Opportunity both continue to roam the red planet, while Cassini gets closer and closer to entering orbit of Saturn this July. Keep up with the Mars rovers at http://marsrovers.nasa.gov/home/index.html. See the latest Saturn images at http://ciclops.lpl.arizona.edu/.