Practice English Speaking&Listening with: Beyond the Solar Eclipse: Lunar Eclipse Science with NASA’s LRO by Benjamin Greenhagen

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I'm gonna talk a little bit about some science that's coming back from the

Lunar Reconnaissance Orbiter. We got some press this summer with the great solar

eclipse that came up across the continental United States. This is an

image taken from lunar orbit with our high-resolution camera of the Earth

showing the eclipse near the point of greatest totality. So we got some press

from that and we want to talk about a little bit of different type of eclipse

that we've a little less coverage on and that's lunar eclipses and why they're so

special to lunar science. So eclipse just means you're in shadow. Solar eclipse

you're in the shadow of the Moon on a particular place on Earth. For lunar

eclipse you are in the shadow of the Earth and the entire near side of the

Moon is in eclipse is in shadow and they progress in stages. The plot down here in

the lower left hand corner shows the two different types of eclipses. As you start

to enter the Earth's shadow you're in a penumbral eclipse. Once you enter the

center part of the shadow you enter the umbral eclipse and the total eclipse.

Great thing about lunar eclipses they can be seen anywhere on Earth that can

see the Moon and they last a long duration. The total eclipses can be up to

about a hundred and five, hundred and six minutes. Important to keep in mind lunar

eclipses always occur during the full moon and lunar eclipses only affect the

near side. So why are these eclipses special? Well they give us a very rapid

transition in temperature on the surface of the Moon and the surface of the Moon

has interesting thermal physical properties. The regolith, and we just

heard from Amanda a few minutes ago, as this very powdery dusty material and

it's in vacuum so it's thermo physical properties are very insulating, it

basically is as insulating as aerogel and it changes its temperature very

rapidly. There's also rocks on the lunar surface and they change their

temperature more slowly. Because we're in this very short duration lack of

sunlight we get this quick thermal pulse which allows us to investigate different

levels within the in the soil as well, whereas if you look

at the entire rotational period in moon, about 29 days, you're getting a thermo

pulse that goes down to about 30 centimeters. During the eclipse it's just

a couple centimeters. And so we can sense the upper part of the regolith and also

smaller rocks than you can with the full day/night cycle. So we want to use this

data to understand the structure of the very near surface, how fluffy it is, how

rocky it is, and look at some different interesting lunar phenomenon and, and

what their thermal physics can tell us about that. So LRO is in a great spot to

view lunar eclipses. We're orbiting the Moon, and so we can get very

high-resolution data and fortunately LRO is also designed to survive lunar

eclipses, so we have plenty of power to be active for for most of them. We've

been active for five of seven of the total eclipses to date. Because we are so

close we can't view every area that's in eclipse, we're limited to a very narrow

orbit tracts and when we go over each of these areas we basically get one orbit

during the total eclipse and then we'll get another orbit which is either when

you're entering or exiting the eclipse. And so we we choose our observations

very carefully based on what landforms are near the orbit tracts and what their

thermal physical properties are. The map on the right is showing the rockiness or

fluffiness of the surface. The instrument that we use during eclipses is the

diviner lunar radiometer. It's a temperature sensor it has nine spectral

channels, two of them measure visible light and seven of them measure infrared

light from the mid infrared all the way out into the far infrared. And because we

have these spectral channels we're able to measure the full range of

temperatures on the Moon which has the most extreme temperature variations of

any place we know of. There's permanent shadow reaches near the poles that are

just called a 17 Kelvin that we measured with diviner and then the equatorial

regions can be up over 400 Kelvin. An important aspect of this is that diviner

can point independent of LRO. So LRO is at a very standard nadir pointing

orientation to save heat and to a lesser extent power, during eclipses and we use

diviner to look off to the side our own instrument.

All right. So what do we see? I pulled out an example here, this is going over a

relatively young lunar crater called Kepler crater, so as we get into the

eclipse it's a kind of mid-morning, the day, it's daytime surfaces warm, we enter

the penumbral eclipse, the partial shadow and the surface starts to cool off. Once

you're in the total eclipse the surface cools off very rapidly. If you look at

the scale bar we've cooled off 200 Kelvin in these fluffy areas around the

crater. In the crater itself it's staying warmer because there are more rocks

there and that's one of the things we're looking at for this particular example

is the distribution of small pebble sized blocks. And then after the eclipse

the surface rapidly warms up again. Each one of these is two Earth hours apart

which would be nominally about six lunar minutes apart. And another interesting

phenomenon we've been looking at are these thermal anomalies that were

discovered by Josh Banfield a few years ago. Basically every fresh impact crater

on the moon disturbs an area of tens to up to about 80 crater diameter away

that's really only visible in the thermal inertia maps, and so it's fluffed

up is this large area that extends around the small crater, and we've

identified these by looking at the temperatures in the pre-dawn data, so

right before dawn this temperature difference is greatest for these

disturbed areas, there are these colder blue lines, typical regolith is this red

line. But when we look at these areas in eclipse they're actually warmer during

the eclipse because that means although they have a fluffier structure generally

the very top part actually has to be less fluffy, and so we're trying to

figure out exactly how that works for understanding that. All right, you can

start the plot on the left. These are actually Earth-based thermal telescope

movies and this plot here on the left is Kepler and you're gonna see something

very similar to what we saw with the diviner data, rock staying warm, regolith

gets cooler. If you could start the one on the right as well. This is Reiner

Gamma, this is a space weathering anomaly, it's an albedo anomaly, and here we're

looking to see if there were thermal physical differences and once you get

in eclipse you see the feature just completely

disappears and you see the background rocks. So here we're using ground-based

telescopes that were measured at the same time as the diviner observations to

get this higher temporal resolution so there's a nice synergy between the two

different types of observations. All right

so, kind of in summary, we're getting really nice data from the lunar eclipses.

We may not be able to do this very much longer going forward. LRO has been up

there for over eight years, its batteries have degraded a little bit and so we're

at the point where total eclipses are probably off the table but we're still

gonna look at partial eclipses and we're also evaluating the data as we enter the

eclipse and we exit the eclipse to get additional information as well. So with

that I'll take any questions. Thank you.

The Description of Beyond the Solar Eclipse: Lunar Eclipse Science with NASA’s LRO by Benjamin Greenhagen