Copyright 1995
Here are the questions I have gotten pretty wrong in my haste!
I saw a double rainbow with the colors of the inner one reversed. Was I imagining this?" Several careful readers caught my blooper that it is unusual for double rainbows to have reversed colors. In fact, this is the common way for them to appear!
How many stars are there in the universe? One irate reader has taken me to the woodshed because I have been woefully inconsistent in making this calculation. In questions q2865.html, q2223.html, q2051.html, q1120.html, q245.html I use several different estimates for the number of galaxies in the universe. I use the Hubble Deep Field image to estimate 80 billion galaxies; or about 100 billion galaxies; or 50 billion galaxies and all of these are well within the counting errors based on how the estimate was arrived from the data. When you consider that there are many more dwarf galaxies than the bright ones we see, even these estimates can be lower limits by a factor of 2 to 10. We really don't know how to count ALL of the galaxies in our visible universe to get a number reliable to within a factor of 10! My answers reflect this. As for the average number of stars in these galaxies...mostly dwarf galaxies...you get a few billion stars, but the massive galaxies like the Milky Way can have as many as a few trillion stars...mostly dwarf stars. The average large galaxy probably has of the order 100 billion stars...give or take a few hundred billion! So, for the 100 billion bright galaxies based on the Hubble data, you get an estimate for the total stars in the visible universe that is of the order 100 billion galaxies times 100 billion stars/galaxy or 10,000 x 10^18 stars. This probably an under estimate because most galaxies are dwarfs, so they might contribute 100 billion more galaxies with a few billion stars or a total of 100 x 10^18 stars. I think that quoting a number in the mid-range between these two, say 10^21 stars would be just fine, but the actual number could be 10^22 or even 10^23. That's the best that any astronomer could probably do, considering that the Hubble Deep Field only surveyed 1/36 millionth of the sky!
Does the Earth stay in the same spot in the sky as seen from the Moon. The first time I answered this question in 1996 I said that the earth would slowly drift across the sky. The second time I was asked to answer this question I immediately said 'Yes', but my publisher at W.H. Freeman pointed out that I had provided the bogus 'No' answer in my book manuscript, so now I am forced to recant the wrong answer. I can honestly say I do not recall how I ever thought the answer was 'No' in the first place! Several of my astronomer friends who 'do' planetary astronomy assured me that the Earth DOES stay put in the sky, as a very simple exercise with two balls will show you it does. I seem to recall in getting my first wrong answer, I used some mental visualization of the problem rather than the two-ball method to represent the moon's and earth's motions.
Can you have more than 2 Blue Moons in a year? Of course you can! In fact in 1999, 2018 and 2037 the months of January and March will have Blue Moons. I have not recanted my definition of the Blue Moon as the second Full Moon in a calendar month. I know this is not technically correct after Sky and Telescope published their article a few years ago...but I really don't care. I like the definition I am using because it is very intuitive and easy to explain. So sue me!
Previous questions about the analemma were pretty awkward, to be polite. In Question 104 I drew the sunrise on the western horizon. This usually doesn't happen as any grade school student can tell you instantly. Also, Question 2087 also got this wrong. I have never taken the time to really understand what the analemma is all about, so you should probably read the Sky and Telescope article I refer to about them to get the real scoop! There are probably other errors in my explanation too.
In my explanation for the Green Flash I mistakenly used the word 'diffraction' when I meant 'dispersion'. Diffraction has nothing to do with the effect.
Typo alert!! In the question about the star classification sequence OBAFGKM, I mentioned a date, '1990's ' which should have been "1890's".
Ben Saucer noted to me that in Question 1506 and Question 867.html about using a lunar eclipse to date the crucifixion of Jesus Christ that some authorities advocate a Wednesday afternoon (Nissan 14) crucifixion. My only reply is to read the Nature article I cite. They seem to provide cogent arguments for their dating scheme that seem to rule out this possibility.
Libbie Hughes tells me that in Question 2185 Marduk was in fact Jupiter, and Ishtar was Venus. Mercury was Inanna, and Saturn was known as the Black Sun. The Sun and Moon were Sin and Shamesh. The planets did play a major role in the Tigris/Euphrates region, perhaps even greater than that of the Sun and Moon!
Ilya Taytslin just pointed out to me that in Question 2704 that I should have said ammonia instead of methane, because ammonia (NH3) is nitrogen rich not methane (CH4). Thanks for catching this silly error!
Ed Cannon tells me in Question 2836 I gave 1997 as the date for a 1960's Ohio Fireball. A pretty lame typo.
Jeff Luck and Nils Olof Carlin both tell me about a howler in Question 2617 about the barycenter of the Pluto-Charon system. I did the right math but rushed to type up the wrong answer saying that the barycenter is 400 miles below the surface of Charon. It is actually about 700 miles below the surface of Pluto. Sorry about the sloppiness on my part.