Latest / PlanetGeo: The Geology Podcast / Manhatten-henge - Dr. Jackie Faherty (GeoShort)

Transcript

Manhatten-henge - Dr. Jackie Faherty (GeoShort) · PlanetGeo: The Geology Podcast

• 0:04
  SPEAKER_00: Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.
• 0:41
  SPEAKER_00: Today we talk a bit about Manhattan Henge, which you may or may not have heard of, but it's just a really interesting phenomenon and is a really cool way to understand how Earth rotates.
• 0:52
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• 0:55
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• 0:59
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• 1:01
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• 1:04
  SPEAKER_00: We are at Planet Geocast.
• 1:05
  SPEAKER_00: That's at Planet Geocast with a C.
• 1:09
  SPEAKER_00: All right, let's get to Dr.
• 1:10
  SPEAKER_00: Fardy.
• 1:11
  SPEAKER_00: Okay, so is it wait, is it Manhattan hedge or henge?
• 1:16
  SPEAKER_00: Henge.
• 1:17
  SPEAKER_01: Oh play on the word stone henge.
• 1:19
  SPEAKER_00: Jesse, what are you doing?
• 1:20
  SPEAKER_00: Like, of course it's henge, not hedge.
• 1:23
  SPEAKER_01: What are you doing?
• 1:26
  SPEAKER_01: Just beat into it, you know?
• 1:28
  SPEAKER_01: You know my gosh.
• 1:30
  SPEAKER_00: I think that's a that's an honest question.
• 1:32
  SPEAKER_00: And I don't deserve the crap I'm getting for this right now.
• 1:35
  SPEAKER_00: Okay.
• 1:36
  SPEAKER_00: You didn't get the play on the words, did you?
• 1:38
  SPEAKER_00: That's your problem.
• 1:38
  SPEAKER_00: I did get it, but I was just confirming that I got it.
• 1:41
  SPEAKER_00: That it was actually a play on words and not I don't want to put my foot in my mouth here.
• 1:44
  SPEAKER_00: So, okay, Dr.
• 1:45
  SPEAKER_00: Faraday, Manhattan Henge.
• 1:48
  SPEAKER_00: What's up with this?
• 1:51
  SPEAKER_01: It's a really cool sunset moment, frankly.
• 1:55
  SPEAKER_00: It's uh So that but this is also this is like some you you started a kind of a social media sort of campaign about this thing too, right?
• 2:02
  SPEAKER_00: Like so can you kind of give us the describe what it is and and what people like about it, I suppose?
• 2:08
  SPEAKER_01: Yeah, and I I definitely cannot take credit for Manhattan Henge.
• 2:12
  SPEAKER_01: The person that started it is Neil deGrasse Tyson, who's the director of the Hayden Planetarium, and he started spreading the word about it in early 2000s.
• 2:24
  SPEAKER_00: Okay.
• 2:24
  SPEAKER_01: And I joined the American Museum of Natural History as a volunteer as a kid right out of college.
• 2:31
  SPEAKER_01: And when I did in the like 2000s era, I he was emailing the department about it and no one was really paying any attention.
• 2:42
  SPEAKER_01: But I would go out every year on these days of the year where the sun sets perfectly aligned with the grid of New York City.
• 2:52
  SPEAKER_01: So perfectly aligned with all of these gorgeous buildings.
• 2:56
  SPEAKER_01: And when the sun is low in the sky, you get gorgeous sunset.
• 3:00
  SPEAKER_00: So the sun is like if you're looking between skyscrapers and Manhattan, the sun is setting straight down between them.
• 3:06
  SPEAKER_00: Is that what's going on?
• 3:08
  SPEAKER_01: No, that's actually a misnomer that a lot of people ask.
• 3:10
  SPEAKER_01: So I'm glad that you said that because sometimes I say it and I realize that it does sound that way.
• 3:14
  SPEAKER_01: It comes at an angle because New York City is not the equator, and this is not the equinox.
• 3:20
  SPEAKER_01: If that were the case, it would come straight down in a vertical ascent.
• 3:25
  SPEAKER_01: But instead, what you get is the sun comes at an angle from the from the south as it's setting north and it crosses where the grid of Manhattan is.
• 3:38
  SPEAKER_01: And so right before the sun kisses the grid of the city, it starts to peak between the buildings, and you only catch it between your buildings right before it sets.
• 3:52
  SPEAKER_01: And so you'll so it's it's not like you're watching the sun all day striking the middle of the building.
• 3:59
  SPEAKER_01: It's a surprise moment.
• 4:00
  SPEAKER_01: You're in the middle of the streets, you're waiting, you're waiting, you're waiting, you're seeing the valley of the city of New York start to brighten in different gorgeous colors.
• 4:09
  SPEAKER_01: And then about 10 to 12, maybe 15 minutes before the uh the sun is supposed to go below the horizon, you start to see its light start shining at you as it emerges from the south, going towards the north.
• 4:25
  SPEAKER_01: And then at the moment of sunset, it's right between your buildings.
• 4:30
  SPEAKER_01: The bottom of it is kissing the grid.
• 4:32
  SPEAKER_01: And then I do another calculation where the middle of the sun kisses the grid, and then it keeps moving north and sets.
• 4:39
  SPEAKER_00: And you mean by grid, you mean the horizon.
• 4:41
  SPEAKER_00: It's hitting the street.
• 4:42
  SPEAKER_00: The the bottom is at the street level.
• 4:44
  SPEAKER_00: Is that what you mean by grid?
• 4:45
  SPEAKER_01: No, I mean actually the New York City, Manhattan is a gridded city with north-south avenues and 90-degree angle cross streets.
• 4:55
  SPEAKER_01: So you have a literal grid of a city.
• 4:59
  SPEAKER_01: There's lots of gridded cities in the world, it's kind of more of a modern thing, I think.
• 5:04
  SPEAKER_01: Uh though the Romans did it, huh?
• 5:07
  SPEAKER_00: Sure.
• 5:07
  SPEAKER_00: Yeah, more recent cities are often gridded.
• 5:09
  SPEAKER_00: Yeah, sure.
• 5:10
  SPEAKER_01: Yeah, gridded cities, it was an efficient way to proceed in developing a city.
• 5:17
  SPEAKER_01: In the 1800s, when they made this decision to grid the city of New York, they didn't have to.
• 5:23
  SPEAKER_01: They had all these kind of squares and these circles, and they could have just followed that.
• 5:28
  SPEAKER_01: And Broadway is this old um Native American trail that skates the whole of the city, and they actually kept that.
• 5:38
  SPEAKER_01: But they decided that 90-degree angles between these the long avenues and the cross streets was the way to do the city.
• 5:46
  SPEAKER_01: And as soon as they did that, they created a bullseye for the sun to hit because they're east-west cross streets with a long view towards New Jersey, which has a relatively low skyline, and so you have a fairly flat sky horizon to aim for.
• 6:03
  SPEAKER_01: So when I say it kisses the grid, it just kisses the middle of this beautiful city of Manhattan in between the buildings, and it does so over New Jersey.
• 6:17
  SPEAKER_01: When does this happen?
• 6:18
  SPEAKER_01: There are two dates, and it's symmetrical because it happens on either side of the summer solstice.
• 6:26
  SPEAKER_01: So it happens uh May 29th or around there.
• 6:31
  SPEAKER_01: There's usually just a plus or minus one day, and then July 13th, again, plus or minus one day.
• 6:38
  SPEAKER_01: And I should say Neil is the one that coined the term.
• 6:41
  SPEAKER_01: He's the one that got people initially excited, but I took over doing the calculations for when it was going to happen uh several many years ago.
• 6:49
  SPEAKER_01: I don't remember what year I started doing it, but then I started doing it.
• 6:52
  SPEAKER_01: I started running a public program, and now it's a super holiday for people to come visit near.
• 6:58
  SPEAKER_00: Do you see a lot of people out on the streets?
• 6:59
  SPEAKER_00: I have two questions.
• 7:00
  SPEAKER_00: Do you see a lot of people out on the streets and and watching this?
• 7:02
  SPEAKER_00: Is this or is there like a viewing event where you can go to and and you can watch this happen?
• 7:07
  SPEAKER_01: It's crazy how popular it is.
• 7:10
  SPEAKER_00: Yeah, okay, cool.
• 7:12
  SPEAKER_00: So cool.
• 7:12
  SPEAKER_01: The cops get involved.
• 7:13
  SPEAKER_01: What you see is this like phenomenon of people, you have to be in the middle of the street to see it.
• 7:19
  SPEAKER_01: So that adds to the joy and the fun, where some people really know what's up.
• 7:23
  SPEAKER_01: And it's a photographer's holiday.
• 7:25
  SPEAKER_01: So photographers really know what's up, and they'll be like well set up in a couple of key locations.
• 7:31
  SPEAKER_01: And I've given away my favorites so much in various media interviews that they're just now absolutely mobbed.
• 7:39
  SPEAKER_01: I mean, thousands of people will be there.
• 7:41
  SPEAKER_01: Cameras will be set up two hours before, and frankly, the my favorite spot, which I do tell everybody about, is illegal.
• 7:48
  SPEAKER_01: Uh, but now it the cops try and break it up, and then everybody comes back.
• 7:54
  SPEAKER_01: It's a whole charades thing.
• 7:55
  SPEAKER_01: And then you're perched above Grand Central, which is my favorite spot.
• 7:59
  SPEAKER_01: And so perched above, but you're kind of you're basically in the streets, sort of, it's just where the cabs are allowed to go.
• 8:04
  SPEAKER_01: Cameras are all set up there, and then so many people show up that they block the entire path for the cab, so the cabs can't go by.
• 8:11
  SPEAKER_01: You look down, and there's people just getting ready to to to line the street at the moment of sunset, traffic stops, buses stops, cabs stop, and there's people that know what's going on and people that don't.
• 8:23
  SPEAKER_00: Oh, that's so cool.
• 8:24
  SPEAKER_00: That's they talk to each other.
• 8:26
  SPEAKER_00: So let's go back to basics because this is like an amazing way to teach you know something about the orbital dynamics of Earth.
• 8:32
  SPEAKER_00: Like, why does this happen?
• 8:34
  SPEAKER_00: Can you give us that in 30 seconds?
• 8:36
  SPEAKER_00: Like, what's going on here?
• 8:37
  SPEAKER_01: Yeah, so the thing I try and get people to understand when they think about this is that the sun sets in a different position every day.
• 8:46
  SPEAKER_01: And it's actually six months in one direction, and then it's six months repeating itself just backwards.
• 8:52
  SPEAKER_01: And that is because it all comes down to one thing, and that is that the earth is tilted by 23 and a half degrees relative to the plane of the sun, of how the sun is rotating.
• 9:06
  SPEAKER_01: So we don't rotate at the same angle that the sun rotates, basically.
• 9:12
  SPEAKER_01: And so we lean away from the sun sometimes, and then we lean towards it as we're going around.
• 9:20
  SPEAKER_01: So that means that there's sometimes when the sun is gonna set very far north of east, rise north of east, and that I had to think about that.
• 9:33
  SPEAKER_01: It'll set it will set north of west, or it'll set east uh south of west.
• 9:40
  SPEAKER_01: And that just depends on the time of year that you're in.
• 9:43
  SPEAKER_01: And it's because we are tilted by 23 and a half degrees, so the sun will not set in the same position every day, it'll set in a different spot, north or south of due east or west, if you're looking at sunrise or sunset.
• 10:01
  SPEAKER_01: Because the other thing is that there is a reverse Manhattan Henge where you can catch the sunrise on the grid of the city.
• 10:09
  SPEAKER_01: Okay, yes, and I've just been telling people those dates.
• 10:13
  SPEAKER_01: That's a is that a big deal too?
• 10:16
  SPEAKER_01: It's less popular in part because it's winter, so it's cold and no one wants to get up early.
• 10:21
  SPEAKER_01: And you have to look towards the east, which means you're looking towards the boroughs to the east, which is Queens, the Bronx, Brooklyn, and they have a lot more topography.
• 10:31
  SPEAKER_01: There's a lot of tall buildings, there's big landscape, there's geology.
• 10:35
  SPEAKER_00: You know, you guys, the stuff you guys do, there's like there's geology in the way of your astronomy rocks and rocky things, and so it's the same reason we have seasons, right?
• 10:45
  SPEAKER_00: And and people kind of intuitively make that make sense to people.
• 10:48
  SPEAKER_00: But I I think highlighting the fact that the sun is actually setting in a very different spot every night is important, and that's interesting.
• 10:55
  SPEAKER_01: That's cool.
• 10:55
  SPEAKER_01: Yes, and well, I was gonna say the other thing on this is that uh it is just like the seasons, it's the same concept of why we have seasons, and it is symmetric on either side of the summer solstice, which is why it's May 29th and July 13th.
• 11:14
  SPEAKER_01: By the summer solstice, there's something that I call the Manhattan henge effect.
• 11:18
  SPEAKER_01: So, by the calculation of the date, May 29th is the first date that the sun sets so far north that it crosses the projecting grid of New York City across the sky, 93 million miles towards the sun, so that the sun will cross the coordinate grid of Manhattan.
• 11:38
  SPEAKER_01: And then every night, every night between May 29th and July 13th, the sun is between the buildings before it sets.
• 11:46
  SPEAKER_01: It's just a little higher, a little higher, a little higher until the summer solstice, where it reaches the highest that it can be when it crosses your buildings, and then it's lower, lower, lower.
• 11:57
  SPEAKER_01: And July 13th is what I call the goodbye to the grid sunset moment.
• 12:02
  SPEAKER_01: Because at that point, it's the last time that the sun will set so far north that it gets to the point where it'll cross into the grid.
• 12:12
  SPEAKER_01: And then after that, it's like you're you're towards the winter month, towards you're heading towards fall and then winter, and then you come back around towards the spring, and it arrives again at the location of the grid of Manhattan.
• 12:28
  SPEAKER_00: So that's so cool, very cool, very cool.
• 12:31
  SPEAKER_00: So people can follow.
• 12:32
  SPEAKER_00: Science is so cool, Jesse.
• 12:34
  SPEAKER_00: So cool, right?
• 12:35
  SPEAKER_00: It's so cool.
• 12:36
  SPEAKER_00: And so people can find well, we've talked about these dates, but people can find this information on your Twitter and so I usually list the dates on my my website.
• 12:47
  SPEAKER_01: I have a Manhattan henge page, and then you can always follow me on Twitter and I tweet about it.
• 12:52
  SPEAKER_01: And the other thing that I I've done this lesson with school kids where I teach them how to calculate their own henges.
• 12:59
  SPEAKER_01: It because Manhattan Henge is popular because everybody loves Manhattan.
• 13:02
  SPEAKER_01: Well, you guys might not.
• 13:04
  SPEAKER_01: I love Manhattan.
• 13:04
  SPEAKER_01: A lot of people in the world love Manhattan.
• 13:06
  SPEAKER_00: You people from New York love Manhattan.
• 13:09
  SPEAKER_01: It's not just you people from New York, a lot of people across the world love Manhattan.
• 13:13
  SPEAKER_00: All right, all right.
• 13:14
  SPEAKER_01: The point being, Chicago has a henge for you Midwesterners.
• 13:18
  SPEAKER_01: Hey, there we go.
• 13:19
  SPEAKER_00: That sounds fun.
• 13:21
  SPEAKER_01: And Chicago Henge is actually around the equinox, so it happens.
• 13:25
  SPEAKER_01: Uh, you just missed it.
• 13:26
  SPEAKER_01: It was it was right around the first day of fall, and the autumnal equinox was September 21st.
• 13:33
  SPEAKER_01: But aside from that, you don't need too much to calculate exactly where the sun will intersect something interesting for you.
• 13:43
  SPEAKER_01: So the Manhattan is such a big city, and there's so many interesting buildings, but the whole point, like people used to do this.
• 13:50
  SPEAKER_01: This is why Stonehenge exists.
• 13:52
  SPEAKER_01: They built a structure to capture the sun on its sunrise moment on a very important day, which was the summer solstice, because you want to know what the longest day of the year is, and you want a marker for that because you didn't have like yeah, you didn't have GPS, you didn't have calendars, we didn't have anything that was helping us keep track of time.
• 14:12
  SPEAKER_01: It was figuring out the position of the sun.
• 14:14
  SPEAKER_01: And this is our little clock in Manhattan, but you could calculate it.
• 14:18
  SPEAKER_01: And so I have kids in Queens do this that aren't on the grid of Manhattan, I have kids in Brooklyn do it.
• 14:23
  SPEAKER_01: I teach teachers how to bring this up with their kids and then teach a lesson on it because it's a really good earth science lesson.
• 14:30
  SPEAKER_00: It is, yeah, that is.
• 14:32
  SPEAKER_00: That's a great earth science lesson.
• 14:33
  SPEAKER_00: Absolutely.
• 14:34
  SPEAKER_00: Okay.
• 14:34
  SPEAKER_00: Well, thanks, Jackie.
• 14:35
  SPEAKER_00: That's really useful.
• 14:37
  SPEAKER_00: All right, that's a wrap for today's episode.
• 14:40
  SPEAKER_00: Tune in next week for a full interview with Dr.
• 14:42
  SPEAKER_00: Jackie Fardy.
• 14:43
  SPEAKER_00: Follow us, like, subscribe, and please send any questions you have to for either Chris or I or our guests to planetgeocast at gmail.com.
• 14:53
  SPEAKER_00: That's planetgeocast at gmail.com.
• 14:55
  SPEAKER_00: We love hearing the questions and interactive with you all.
• 14:58
  SPEAKER_00: Peace.