Lunar Eclipse, Meteor Shower, Arsenic-Tolerating Bacteria, and the Number of Stars in the Universe

Dear Friends,

It’s been an exciting year in space science, and my apologies for the delay in getting the latest news to you. But a couple recent developments have gotten a lot of press, so I want to update you on those, as well as on the upcoming total lunar eclipse, which will be visible throughout North America, and the annual Geminid meteor shower. So here are the contents for this e-mail:

1. Monday Night Dec. 20: Total Lunar Eclipse
2. Geminid Meteor Shower, Night of Dec. 13
3. Arsenic-tolerating Bacteria Make Big News
4. Estimated Total Number of Stars Grows Larger

As always, I welcome responses, so don’t be afraid to comment.

Best wishes,
Jeff

1. Monday Night Dec. 20: Total Lunar Eclipse
If your skies are clear, plan to stay up late on the night of Monday, Dec. 20, or take a nap and then get up to view what should be a great total lunar eclipse. Remember that you don’t need any special equipment to see a lunar eclipse, though you’ll enjoy looking at the Moon through a pair of binoculars if you have them. Also, because the Moon is so bright, you can see a lunar eclipse even if you’re surrounded by fairly bright lights, so you can just go out and enjoy, then go right back to bed! If you don’t want to stay up for the whole thing, try to watch from the beginning of the partial phase until a bit after totality begins; that way, you’ll see Earth’s curved shadow moving across the face of the Moon, and see the distinct red shadow that engulfs the Moon during totality. For complete information about the eclipse, see Fred Espenak’s Mr. Eclipse page; but here are the basics for planning your evening:

For classroom discussion:

* What is a lunar eclipse? (Answer: It is when the Moon passes through Earth’s shadow. Ordinarily we can’t see Earth’s shadow, since it is a dark shadow against black space. The exception is when the Moon passes through the shadow, and therefore becomes darkened by it.)

* Why does the Moon look dark and red during the total lunar eclipse? (Answer: It looks dark because it’s in Earth’s shadow. It looks red because Earth’s atmosphere bends light in such a way that some of the red light from the Sun still reaches the Moon even during totality; virtually none of the blue light reaches the Moon, so the Moon ends up looking red in color.)

* The night of Dec. 20 is not only the eclipse but it is also a full moon. Is this a coincidence or not? (Answer: not — a lunar eclipse can occur only when Earth’s shadow falls on the Moon, which means the Moon and Sun must be on directly opposite sides of the Earth, which is the condition for full moon. Thus, a lunar eclipse can happen only at full moon. Similarly, a solar eclipse can happen only at new moon.)

* The eclipse ends early in the morning of Dec. 21, which also happens to be the date of this year’s winter solstice. Is this a coincidence or not? (Answer: Coincidence, but pretty cool! In fact, the precise time of the winter solstice is 6:38pm Eastern time on Dec. 21, which is more than 12 hours after the eclipse ends.)

2. Geminid Meteor Shower, Night of Dec. 13
We also have the annual Geminid meteor showering coming up on the night of Dec. 13 (to pre-dawn Dec. 14). Meteor showers are always fun to watch. With thanks to Larry Sessions, I’ll just point you to the EarthSky site for more information.

3. Arsenic-tolerating Bacteria Make Big News
A few days ago, NASA held a much-anticipated press conference to announce a discovery that they said would revolutionize biology and the search for extraterrestrial life. It is indeed a cool discovery: a form of bacteria that can apparently tolerate arsenic, and perhaps even use it in its DNA in place of phosphorus. You can easily find hundreds of articles about it with a quick web search, but I recommend this article from the New York Times. But does it live up to its hype? I’ll let you be the judge, but here’s a quick summary of the key take-away points:

* If it really is able to make DNA with arsenic rather than phosphorus, then it has two important implications: (1) Phosphorus has been thought to be one of the 6 indispensable chemical elements of life on Earth (the others being carbon, oxygen, nitrogen, hydrogen and sulfur), so this organism would show that phosphorus is not quite as indispensable as we thought. (2) It broadens the range of chemical possibilities for DNA — and hence for hereditary material in general — which in principle broadens the range of possible conditions under which we might find some form of extraterrestrial life.

* It appears to tolerate the arsenic, but it does not prefer it to phosphorus. This may or may not mean that arsenic is the less-ideal chemical choice, which may or may not have implications to where extraterrestrial life might be found. How’s that for waffling?!

* Contrary to a few reports you may have seen, this is NOT some new and novel life form, and it does NOT imply any separate origin of life on Earth. This bacteria fits into the well-established “tree of life” and clearly shares a common ancestry with all other known life on Earth.

4. Estimated Total Number of Stars Grows Larger
Another much hyped story of the past week concerns a new estimate that may triple the estimated number of stars in the universe; you can read about it in this New York Times article. Again, very cool and interesting. But perhaps not Earth (or universe) shattering. The new estimate does not change our estimate of the universe’s overall number of galaxies or mass; it just suggests there are more low-mass stars and fewer massive ones. And we already know that there are roughly as many stars in the observable universe as grains of sand on all the beaches on Earth, and even a tripling doesn’t change this basic fact, since that estimate is based on orders of magnitude and can easily be off by a factor of 10 in either direction.

By the way, you’ll see in the article, and other articles, that the “extra” stars are referred to as “red dwarfs.” This is an absolutely terrible name, since it makes most people think of white dwarfs, or dwarf planets, or brown dwarfs, or any of the many other “dwarfs” that astronomers tend to talk about but that bear very little relationship to one another. So don’t be mystified: a “red dwarf” is simply astronomer-speak for a star with relatively low mass (less than about 20% that of the Sun). But it’s still a star, shining because nuclear fusion is converting hydrogen into helium in its core.

Thanks so much for your time!