torah study - What level of understanding is required in "learning" for purposes of making a siyum?

When learning as part of a coordinated group siyum, what level of understanding of the material is expected/required? How do you know if you've done enough to fulfill the mitzvah? Is it about effort expended, or about reaching a certain level of accomplishment (e.g. that you could pass some sort of test on the content)? How does somebody who is not already extremely learned (like, say, a ba'al t'shuvah), but who wants to help, know if his efforts will be useful?

This answer addresses learning in English rather than Aramaic and says it's more than just reading the words, which makes sense to me, but that doesn't actually say what level of proficiency one should be able to demonstrate.

molecules - Atomic properties

This may be a very broad question. I always asked myself how scientists manage to find out the exact molecular structures of for instance water or carbohydrates. How do they know? How do they know the angle between the bonds in water? Is there a classical example demonstrating and substantiating current knowledge on molecular level of structure?

The if we go to atoms, how do people know what charge an ion has? How can be know we have atoms with 7 protons for instance?

Probably there are zillion ways required to find out, but could you give me some general examples?

halacha - You accidentally broke your fast. Now what?

What are you supposed to do if you inadvertently broke your fast*? Do you:

1. keep going;



2. extend it (if so, how long);


3. cancel it (if so, do you make it up a different day)?

_{*This question is for day-fasts only.}

Answer

The Mishna Brura OC 549 sk 3 says to continue fasting if you accidentally ate.

In OC 568 sk 3 he says you can still say Aneinu at Mincha if it is a public fast day (as opposed to a personal one).

In OC 568 sk 8 he says that you do not need to fast again on a different day for accidental eating on the public fasts as well as any personal fast that has a fixed date (eg Yahrtzeit).

This halacha is not limited to Yom Kippur and Tish'a b'Av, but applies to "minor" fasts, as well.

halacha - Mayim Achronim at The Pesach Seder

Why in the Order of the Seder (that is Kadesh urchatz…) do we not include Mayim Achronim while we do we include the regular washing and the washing before dipping the vegetable into saltwater when all three are Halachic requirements? Why does the Mayim Achronim get ignored in the List of Things to do?

spectroscopy - Is it true that heavy water is not blue?

I believe I saw this claim somewhere on the internet a long time ago. Specifically, it was claimed that the difference could be observed by filling one long, straight tube with light water and one with heavy water, and looking through both tubes lengthwise (so that light has to travel through the tubes' lengths before reaching the eye), whereupon the light water would appear blue as it does in the oceans, and the heavy water would not. The explanation given was that heavy water has a different vibrational spectrum because of the greater mass of the $^2$H atom, which seemed perfectly plausible.

However, I am no longer able to find a source for this claim, which is strange because if it were true, surely it would not be so difficult to find a source?

Answer

Based on your description, I may have found the article you originally saw, or at least one very similar.

Researchers from Dartmouth College published a paper$\mathrm{^1}$ in which they report, among other things, the results of viewing sunlit white paper through two 3 meter lengths of plexiglass; one filled with $\ce{H2O}$ and one with $\ce{D2O}$. Sure enough, because of the lower frequency of the maximum absorption of $\ce{D2O}$ in the red to near IR wavelengths, the blue color that is characteristic of $\ce{H2O}$ is far less pronounced in $\ce{D2O}$. This website is based on the published paper and additionally shows a photograph of the blue colored $\ce{H2O}$ on the left with the far less colored $\ce{D2O}$ on the right:

1) "Why is Water Blue", Charles L. Braun and Sergei N. Smirnov, J. Chem. Edu., 1993, 70(8), 612

product recommendation - Where can I find the current water level of the Kineret to see the effect of mentioning Morid Hageshem?

Throughout the winter we pray Mashiv HaRuach UMorid HaGeshem. My understanding is that it is said for Eretz Yisroel dwellers (unlike V'sain Tal Umatar LBracha which is said for your locale). As we pray for it I am interested in knowing if there is an online source to find out what is the current water level of the Kineret?

Answer

See:

marriage - Having children when both parents are Tay-Sachs carriers

This is an obvious CYLOR question, but I am interested in whatever halachic information is available out there.

Suppose a couple got married without ever getting genetically tested for Tay-Sachs. When they decide to have a child, they are both tested and both turn out to be carriers. Does the mitzvah of having children still apply to them?

Also, is it acceptable for two people who know that they are carriers to get married in the first place?

Answer

When I went for genetic testing, the secular geneticist told me that her rule of thumb was "oh they'll just test each pregnancy and terminate the Tay-Sachs ones." Suffice to say that Rabbi Moshe Feinstein vehemently opposed that logic. His student Rabbi Tendler is therefore opposed to amniocentesis as the couple will then be pressured to terminate -- when according to Rabbi Feinstein it's not permitted to do so. (Note that other rabbis are more lenient in some unfortunate cases.)

I think the majority of Orthodox poskim today will tell you that two carriers really should look for other people to marry. It's the least-bad option. Hence the importance of checking for compatibility well before a relationship gets underway. (Rabbi Feinstein himself recommended finding one's carrier status as soon as one decides that s/he is "seriously of dating age", while the tests could be done earlier he didn't want more anxiety weighing on people. Today Dor Yeshorim removes the stigma by no one knowing their actual status.)

Should a couple realize they're both carriers: Rabbi Feinstein had ruled "if a man has a condition such that, regardless of who he marries, there's a 50% chance that his child will have medical problems but a life expectancy of several decades with treatment ... he should have faith and get married", with others questioning this. That's a far, far cry from saying that a couple who know there's a 25% chance any child they have won't survive preschool age should have "faith."!

In short:

• A couple who know they're both carriers shouldn't get married.



• If they're already married and determine they're carriers, it's reasonable to question whether the mitzva to try to conceive conventionally would apply -- as the emotional cost here is so high. I'd assume many would advise against it.


• Adoption, or IVF with preimplantation testing, are both complex options that may be advisable, pending a couple's consultation with their rabbi.