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LYNN NEARY, host:

One of the UK's leading research labs is asking the public to help answer an important question: Exactly when does the new moon appear? Many religions rely on the new moon to set their calendars and determine the timing for important festivals. The problem is the new moon becomes visible in different places at different times. That's where Her Majesty's Nautical Almanac Office comes in. They are asking people to go outside tonight at sunset and record when they see the new moon. Catherine Hohenkerk works for the HM Nautical Almanac Office. She joins us now from her home in Oxfordshire, England.

Thanks so much for being with us.

Ms. CATHERINE HOHENKERK (Her Majesty's Nautical Almanac Office): Hello, Lynn. It's nice to be here.

NEARY: Tell us something about this project, how it came about and its importance and significance.

Ms. HOHENKERK: Well, it's part of mass experiment that's being carried out for Einstein Year. And we got involved because we could see an application where we could get members of the public worldwide to make observations of the new crescent moon and enter the data into our Web site. So this is not just for the UK, although we are very interested in the northern latitudes, but we we want people all over the world, if possible, to enter this data.

NEARY: Now can't you already calculate the start of the new moon mathematically? Why a moon watch in this day and age?

Ms. HOHENKERK: Well, we know precisely when the instant of new moon is. That's not the problem. The problem is that you cannot see it until it's hours old. So you have to wait until the width of the moon, the crescent, that sliver of light that you see is large enough for you to see with your eye. And that also depends on the relative positions of the Earth--the observer, that is--the sun and the moon and how old the moon is at sunset because you're only going to see it in the evening after the sunset.

So in Washington, the sun will set at 18:44 tonight, and the moon will then set a 19:45. So have an hour. So in Washington, you have a good chance of seeing it this evening...

NEARY: Oh, good. I'm going to be looking up at the sky. What about there in England? It must be early evening there already. Are people out there watching now?

Ms. HOHENKERK: Well, I hope they've been watching. In Glasgow, for example, they only had 20 minutes this evening to see, and so the chances were much less because they've already seen it. The moon was also younger, and therefore the crescent wouldn't have been as wide. That's that sliver of light you see--wouldn't have been as wide, so they have less opportunity. But we are trying to gauge how to predict this for months in the future. And that's why we want everybody to make these observations. And it doesn't matter if you don't see it. If you go out and look and you haven't seen it, we still want you to enter the data into our Web site, which is www.crescentmoonwatch--all one word--.O-R-G, .org.

NEARY: OK. So you enter exactly when you saw--you enter when you saw it?

Ms. HOHENKERK: You enter the time you saw it, and there will be other questions about exactly what you saw. There are various moon symbols to look at to match what you saw; your location, of course. There's also something about your eyesight, whether you've done this many times; your age, because of course it's a factor of how good your eyesight will be. And...

NEARY: And then is this just a one-shot thing? You're doing it tonight and that's it or...

Ms. HOHENKERK: Oh, no, no. We want--hopefully, it'll run a couple of years. And so every month we would like people to go out from new moon and for about three nights until they see it and then enter the information in. And as I say, it's just as important to enter if they don't see as to when they do see it.

NEARY: And then you'll be able to figure out when the moon's going to come out in the future. And that'll help a lot of people calculate their religious events and things like that?

Ms. HOHENKERK: Yes, people like to know when it's going to happen because people like to plan things. And we have predictions at the moment, but they're based on some work that was done about 10 years ago...

NEARY: Catherine, thanks so much for joining us today. We're running out of time.

Ms. HOHENKERK: Oh, lovely.

NEARY: Good luck with your project.

Ms. HOHENKERK: Thank you very much.

NEARY: Catherine Hohenkerk is a mathematician and member of the HM Nautical Almanac Office.

This is TALK OF THE NATION from NPR News. I'm Lynn Neary in Washington.

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