Happy International Year of Astronomy!
Four hundred years ago, in 1609, Galileo built a telescope and turned it to the heavens, making crucial discoveries that helped overturn the ancient belief in an Earth-centered universe. In celebration of the 400th anniversary of these discoveries, the United Nations has designated 2009 as International Year of Astronomy (IYA). Planetariums, science centers, and universities around the world are planning a wide variety of activities for IYA; check your local facilities to find out what is happening in your area.
In addition to scientific opportunities, IYA provides a great opportunity to think about the meaning of Galileo’s discoveries. I’ve written an op-ed on this topic that appeared in yesterday’s Los Angeles Times; it is pasted at the end of this message, following a bit more space news. Hope you enjoy it!
Best wishes,
Jeff
Contents
1. Venus shines brightly for IYA
2. Comet Lulin
3. Minor lunar eclipse, and summer solar eclipse
4. New activities and resources for kids and teachers
5. LA Times op-ed on IYA
1. Venus shines brightly for IYA
If you’ve been wondering about the really bright “star” that is currently shining in the west after sunset, it’s the planet Venus. Galileo’s observations of Venus were particularly important, because they proved that it was orbiting the Sun and not Earth, so it’s rather nice that Venus happens to be shining so brightly for the beginning of the International Year of Astronomy.
To understand what you are seeing a bit better, remember that Venus is closer to the Sun than Earth. Therefore, from our vantage point, it seems to swing back and forth around the Sun. Right now, we are seeing Venus when it is nearly as far to the east of the Sun in the sky as it ever gets (its greatest eastern elongation was on Jan. 14), and if you look at Venus through a telescope, you will see that it is a crescent. The figure below (taken from my textbook, The Cosmic Perspective) shows how Galileo used the phases he observed for Venus to prove that it must be orbiting the Sun. (The “Ptolemaic view” means the Earth-centered view, which was codified in the model of Ptolemy; the “Copernican view” is the Sun-centered view proposed by Copernicus, which Galileo’s discoveries supported.)
Venus will remain prominent in the evening sky for another couple of months. Although Venus takes only 225 days to orbit the Sun, the fact that Earth is also moving as we observe it makes it take a total of 584 days for Venus to complete one full back-and-forth cycle around the Sun in our sky. Therefore, it takes about one-fourth of this time, or a little less than 5 months, for Venus to make its way from a position when farthest east of the Sun (where it was on Jan. 14) until it catches up with the Sun’s position in the sky. Of course, as it gets closer to the Sun in the sky, it will become more and more difficult to see in the glare of sunset.
For Classroom Discussion:
*Study the figure given above that compares the Earth-centered (Ptolemaic) and Sun-centered (Copernican) views of Venus. How did Galileo use Venus’s phases to prove that it orbits the Sun? (Answer: As described in the figure captions, Venus can go through a full cycle of phases — which is what Galileo observed — only if it orbits the Sun. No one noticed this fact before Galileo, because the phases are visible only through a telescope, not to the naked eye.)
*Do we ever see a “full” Venus? (Answer: No, because it is full when it is on the opposite side of the Sun from Earth — which means it is completely obscured by the bright light of the Sun at that time.)
*Do we ever see Venus at midnight? (Answer: No, because at midnight we are looking into space in a direction opposite the direction of the Sun. Because Venus always stays fairly close to the Sun as seen from Earth, we never see it at midnight.)
*In the figure, identify the location of Venus when it was at its greatest eastern elongation in our sky on Jan. 14. (Answer: In the figure of the Copernican view, it’s on the left side between the crescent and quarter positions; to see why it’s in between, rather than at the far left, draw a tangent line from Earth to the orbit of Venus — the point where it touches to the left is the greatest eastern elongation. The figure is not drawn to scale, so your visual estimate will be close but not perfect.)
*When will Venus next be at greatest eastern elongation? (Answer: 584 days after Jan. 14 — which puts it on Aug. 20, 2010.)
*Will Venus be visible in the fall of this International Year of Astronomy? (Answer: Yes, but by then it will have moved to the opposite side of the Sun as seen from Earth [the right side of the Copernican view figure above], which means we will see in the pre-dawn sky, rather than in the evening sky.)
2. Comet Lulin
This recently discovered comet can now be seen with binoculars or a small telescope. It is gradually brightening, and expected to become faintly visible to the naked eye later this month. For information on finding it, as well as its wonderful discovery story, see this NASA Science News article.
3. Minor lunar eclipse, and summer solar eclipse
A lunar eclipse occurs when Earth’s shadow falls on the Moon, which means it can happen only at full Moon — and one happened to occur this morning. Don’t feel bad if you missed it; it was the type of eclipse in which the Moon passed only through the lightest part of Earth’s shadow (the penumbra), so it would have been very difficult to see. Two more penumbral lunar eclipses will occur this summer, on July 7 and August 6. Neither is likely to be worth watching, but in between there will be a spectacular total solar eclipse that, at its maximum, will block the Sun for nearly 7 minutes. However, if you want to see it, you’ll need to travel to China or the western Pacific ocean. Doug Duncan, director of the Fiske Planetarium in Boulder, is leading a trip to see the eclipse in China — highly recommended!
4. New activities and resources for kids and teachers
I have posted several new resources on our Big Kid Science Activities/Resources page, including new interactive tutorials on phases of the Moon and seasons, and long-promised pages (noninteractive) on “secrets of the paintings” in the Max science adventure books.
5. LA Times op-ed on IYA
The following is the text of my op-ed published in the Los Angeles Times, Feb. 8, 2009. Read it here.