Today is Monday,April 20th, 2015

Pre-Class:How long is a year?

What causes the seasons?

http://deepskycolors.com/pics/astro/2011/11/mb_2011-11_Aries.jpg Dust clouds within the Aries constellation.

In This Lesson:The Celestial

Sphere, Seasons, and Moon

(Lesson 2 of 2)

Today’s Agenda

• The Celestial Sphere• Celestial Coordinates• Seasons• Detailed Moon Information• Eclipses

• Where is this in my book?– Pages 19-43, and 189-212.

By the end of this lesson…

• You should be able to locate objects via a celestial coordinate system.

• You should be able to distinguish between a solar/synodic and sidereal time period.

• You should be able to astronomically explain the seasons and the phases of the moon.

• You should be able to describe the moon via a variety of properties.

• You should be able to identify the circumstances under which a lunar or solar eclipse occurs.

Pre-Test

• Grab your computers – we’re going to see how much middle school astronomy you remember.

• Unit 1 Lesson 2 Pre-Test– Username: [firstnamelastname]832– Password: Gleicher[house/apt. #]

What’s your star sign?

• It may seem silly to you at this point, but students in the past have sometimes confused this course (Astronomy) with horoscopes (Astrology).

• They’re so similarly named because they both concern celestial bodies and space.– All those “star signs” are literally stars – they’re

constellations like the one on the first slide.• However, Astronomy is science while astrology

is…not.

The Astrological Signs

• So how’d astrologers pick those twelve star signs?

• Well, they saw those constellations fairly readily in the celestial sphere.– The celestial sphere is the “sphere of stars” that

appears to rotate around the Earth.• The “movement” of the stars (they really don’t move) is

called diurnal motion.

The Celestial Sphere

• Other things early astronomers noticed:– The planets/Sun move through a band of the

celestial sphere called the zodiac.• Those are the “star sign” constellations.

– The stars “rotate” around the North Star (Polaris).• Key: Because the Earth rotates toward the EAST, the

stars appear to rotate WESTWARD through the sky.

– The Sun “moves” through a path called the ecliptic.

The Astrological Constellations

The Celestial Sphere• The earliest astronomers didn’t realize:– The Earth is doing the rotation, not the stars.– The stars are at different distances.

• So stars within constellations are not “related.”• In fact, some many be many light years apart

from each other.

• Now’s probably a good time to discuss two reasons why the stars “twinkle.”– There’s a huge distance between us.– The Earth’s atmosphere and wind can distort

the light a little bit.

The Celestial Sphere

The Celestial Sphere

• How far are the other stars, anyway?– UniverseToday – What is the Closest Star?

• We can get a good sense for that “moving” celestial sphere if we just speed things up to a more human-like time frame.– Celestial Sphere Rotation video

• If we change the time lapse process a little bit, however, we can reveal the rotations of the Earth within the celestial background.– Star Spin video

Aside: Edmond Halley

• Edmond Halley is most well known for his comet.

• He also was the first to confirm that the stars move.

• To do this, in 1718 he compared the positions of stars to those noted (rather accurately) by the ancient Greek astronomer Hipparchus circa 150 BC.– Turns out, in 1800 years, the position of

the star Arcturus had moved just a little bit, but enough to confirm his hypothesis.

https://cbs3weather.files.wordpress.com/2014/04/wx-blog3.jpg

Edmond Halley(1656-1742)

The Horizon System

• One way to locate stuff is the horizon system.– Like a compass, the horizon system helps you find stuff

in the sky by specifying azimuth (direction, like “Northwest”) and altitude (60°, for example).• Zenith, by the way, is straight up (90°). That one IS useful.

• This doesn’t really work for astronomers since, well, stars “move” in the sky.– Astronomers (and telescopes with equatorial mounts)

use right ascension and declination.

The Equatorial System

• The equatorial system is a more logical method because it projects the Earth’s equator onto the celestial sphere.– Instead of specifying points on a sphere via latitude and

longitude like Earth, this sphere is viewed from within.– So the equator is called the celestial equator.

• Any star that is located on the celestial equator has a declination (dec or δ) of 0°.

• A star located straight above the north pole (like Polaris) has a declination of +90°.

• A star located straight above the south pole has a declination of -90°.

Declination

http://www.astronomyforbeginners.com/astronomy/celestialsphere.php

The Equatorial System

• So declination is kinda like altitude in the sky, or like latitude on Earth.

• The equivalent of azimuth (compass direction) or longitude is right ascension (RA or α).– Right ascension is named for the ascent of a star

from the east (or “right”) horizon.• Like arcminutes, every “hour” of right

ascension across the sky is equivalent to 15° of longitude.– 24 hours of RA = 360° of longitude/sky.

Right Ascension

http://www.astronomyforbeginners.com/astronomy/celestialsphere.php

Right Ascension

• Right ascension gets a little tricky.• Think about it: The stars “move” in the sky, so

shouldn’t the “longitude” lines of RA also change?– Sorta.• Right ascension is a fixed point (more next slide).• What changes is the hour angle, which is just a

relationship between the fixed right ascension point and the current sidereal time.

Right Ascension Anchors

• Anyone know where 0° longitude is located on Earth?– The Prime Meridian, which passes through Greenwich, England.

• Anyone know where 0 hr RA is located on the celestial sphere?– The first point of Aries (which is technically now in Pisces),

which is at the intersection of the celestial equator and meridian.

• So RA is anchored to a fixed point and all Dec/RA calculations are made starting there.

• For astronomers, if you can spot a star with a known RA value in the night sky, it doesn’t matter what time it is.– Just use that star’s relative RA to find your object of choice.

The Equatorial System

Eeee…what do I need to know?

• I expect you to know the following:– Astronomers locate objects on the celestial sphere

using a coordinate system.– On Earth it’s latitude and longitude but on the

celestial sphere it’s declination and right ascension, respectively.

– The reason for the change is because dec/RA are fixed on the celestial sphere and thus consistent.

Extra Practice

• Simulation: Sidereal Time and Hour Angle• Celestial Coordinates worksheet (in groups or

pairs)– Still need help? Visit:• http://www.astronomygcse.co.uk/AstroGCSE/Unit4/

DecandRA.htm• http://www.astronomyforbeginners.com/astronomy/

celestialsphere.php

• It took many years to firmly establish that the Earth was rotating, not the stars all rotating around it.– Humanity as a whole just seems to

have a really big ego.• We now know that the Earth rotates

once about its axis…wait…axis?– Just so we’re all clear, Earth’s axis is the

imaginary line that runs from North Pole to South Pole through the Earth.

• Fun fact: At the equator, the Earth rotates at slightly over 1040 mph!

http://science.jrank.org/kids/article_images/space_p12.jpg

Earth’s Rotation

Earth’s Rotation• So Earth rotates about its axis once every…?– 23 hours, 56 minutes, and 4.09 seconds. Huh?

• If you were thinking 24 hours, you’re also right…sorta.– A solar (synodic) day is 24 hours – the type of day you

know.• The Sun goes from a spot in the sky back to the same spot in

the sky.

– A sidereal day (“sid-EAR-ial”) is 23 hours, 56 minutes, and 4.09 seconds.• A distant star goes from a spot in the sky back to the same spot

in the sky.http://astro.unl.edu/naap/motion3/sidereal_synodic.html http://www.astro.cornell.edu/academics/courses/astro201/sidereal.htma

Let’s be clear here…

• “Sidereal” literally means “relating to distant stars.”

• “Synodic” means “relating to conjunctions” of celestial bodies.– When in doubt, remember sidereal is all about the

background stars and not the Sun.• UniverseToday – How Fast Does the Earth

Rotate?

Solar Day versus Sidereal Day

• So what’s the difference?– The reason the sidereal day is

shorter than the synodic/solar day is because the sidereal day is how long the Earth takes to rotate 360°.

– Since the revolution of the Earth around the sun is a curved path, it takes slightly longer for the Earth to re-point toward the Sun, but not as long toward what is effectively a static background star.

http://astro.unl.edu/naap/motion3/sidereal_synodic.html

1 2 = Sidereal Day1 3 = Solar Day

Solar Day versus Sidereal Day

Leap Years• The Earth takes 365.25 days, if we count in

solar days, to revolve around the sun.– A solar year is also known as a tropical year, by

the way.• We make up for the missing time in the

sidereal day by having a leap year every 4 years in the Gregorian calendar:– Unless the year is evenly divisible by 100.– Except when divisible by 400.• So 1900 was not a leap year; 2000 was.

To Be Clear…

• You should know:– The Earth rotates counterclockwise when viewed

from above the North Pole.– The Earth revolves counterclockwise when viewed

from above the Sun.

Seasons

• So now for the big question:• What causes the seasons?– Seriously, what’s your answer?

• Let’s check with some Harvard graduates on their big day.

• A Private Universe

A Private Universe

• Here’s the thing…all those Harvard grads are, well, wrong.

• The Earth’s orbit around the sun is actually quite close to circular.

• Even if it weren’t, the seasons can’t be caused by proximity to the Sun.– If that were the case, the whole planet would experience the

same season all at once.– In reality, right now the Southern Hemisphere is experiencing

the opposite season we are.• Let’s explain this a little bit better than an Ivy Leaguer.

Rotations and Revolutions

• So the Earth rotates about its axis once every sidereal day (23 hr, 56 min, 4 sec).

• The Earth, as you know, also revolves around the Sun once every 365.25 days.– The orbit around the Sun is slightly elliptical,

which means it’s not quite a perfect circle.– As it revolves, it points toward Polaris, which is

commonly known as the North Star.

Rotations and Revolutions

Tilt

• Did you notice the Earth isn’t pointing perfectly North/South while it rotates?– It turns out that tilt is kinda important.

• The Earth is tilted 23.5° relative to the perpendicular of its orbital plane.

• That means, during different parts of the year, certain parts of the planet receive more sunlight per day and are ever so slightly more directed at Sun.– Hence, seasons.

Seasons Model

• [this is your cue, Mr. G – grab your props]

Seasons• For more:– TED: Rebecca Kaplan – Reasons for the Seasons– UniverseToday – Why Are There Seasons?– Veritasium – What Causes the Seasons?– Veritasium – Why Does the Moon Orbit Earth?

Seasons• On the equinoxes, the day length and night length

are equal.– The vernal equinox is on/about March 20.– The autumnal equinox is on/about September 23.

Note: This is Earth’s orbit as viewed from the side.

Seasons• On the solstices, the day/night lengths are at their

extremes (shortest or longest).– The summer solstice is on June 21.– The winter solstice is on December 21.

Note: This is Earth’s orbit as viewed from the side.

Seasons

• What this means is that the Northern Hemisphere gets the most direct solar radiation (known as insolation) on the Summer Solstice.

• The Northern Hemisphere gets the least direct insolation on the Winter Solstice.

• Insolation on the Spring/Fall Equinoxes is relatively equal and “mid-range.”– You even notice the Sun’s “path” across the sky (the

ecliptic) is higher in summer than in winter.

Sun Angle by Seasons

• In Boston, as an example:

http://scienceblogs.com/startswithabang/files/2012/06/sun_angle_seasonal.jpeg

Extreme Solar Angles

• Did you happen to notice something about the angle of the Sun at the poles?– When the Northern Hemisphere is in winter, there

are times when the Artic Circle gets no sunlight all day.

Extreme Solar Angles

• Similarly, at the same time of year, the Antarctic circle gets sunlight for all 24 hours.– And vice versa, when it’s summer in the northern

hemisphere.

Aside: Total Sun?

• The 2002 movie Insomnia by (Christopher Nolan) takes place above the Arctic Circle.

• In reality, suicide rates in Alaska are much higher than other states and some people cite the strange photoperiod as a possible cause.

http://boltechai.net/wp-content/uploads/2014/08/52.jpg

Seasons• Remember that Earth’s orbit about the Sun is slightly

eccentric (not perfectly circular).• At aphelion (July 4), Earth is farthest from the Sun.• At perihelion (January 3), Earth is closest to the Sun.– More on this whole ellipse thing next unit.

Note: This is Earth’s orbit as viewed from the side.

Seasons Practice

• Seasons Interactive• The Seasons worksheet– Can’t remember the Tropics and/or Circles?

Tropic of Cancer

Tropic of Capricorn

Equator

Note that axis tilt is not shown.

Arctic Circle

Antarctic Circle

Moon Phases

• Another product of Earth’s simultaneous rotation about its axis and revolution around the Earth is that the Moon has its own phases.

• Before we explore them, let’s get one thing straight:– Ever hear the phrase, “The dark side of the moon?”– More accurately, it would be a “back side of the

moon,” because the same side of the moon always faces us, though it isn’t always dark.

• Here’s what I mean…

Moon Phases• The Moon rotates with the same period as its orbit.– In other words, it takes 27.3 days to rotate once and 27.3 days to

revolve once.• This is called synchronous rotation.Without Lunar Rotation With Lunar Rotation

Another View

http://upload.wikimedia.org/wikipedia/commons/5/56/Tidal_locking_of_the_Moon_with_the_Earth.gif

Without Lunar RotationWith Lunar Rotation

Moon Phases

Moon Phases – Another Look

• Video: One Year of the Moon in 2.5 Minutes

Moon Phases

• What’s evident from that Moon phase image?– The Moon kinda wobbles.– The Moon gets closer and further during orbit.– Shadows and light pass across the same moon surface.

• So…we’ve got a lot to talk about. A summary:1. General lunar characteristics2. Lunar gravity effects3. Lunar rotation/revolution effects4. Lunar (and solar) eclipses

• To help you summarize this info, use the Moon Details note organizer worksheet.

1. General Lunar CharacteristicsMoon Size and Gravity

http://www.astronomy.org/programs/moon/earth-moon-size.gif

• The moon is about 25% the size of the Earth but it only has 17% of the gravity.– That low gravity means the

moon has no significant atmosphere.• It technically has a little.

– No atmosphere means no protection from meteor impacts, hence all the craters.

1. General Lunar CharacteristicsThe Surface

http://csep10.phys.utk.edu/astr161/lect/moon/luna.gif

• Light areas of the moon are highlands.• Dark areas of the moon are lowlands called

maria (singular: mare).– The name comes from the Latin for “sea,” because

early astronomers thought there were oceans on the moon.

– Apollo 11 landed in the Sea of Tranquility (Mare Tranquillitatis).

• Highlands are composed of anorthosite, which is a different kind of rock from the maria, which are made of basalts from cooled lava flows.

• The dusty/rocky surface of the Moon is overall called regolith.

http://upload.wikimedia.org/wikipedia/commons/thumb/

6/61/Moon_names.svg/2000px-Moon_names.svg.png

1. General Lunar CharacteristicsThe Far Side of the Moon

• Interestingly, the far side of the moon (the “dark” side) appears much different from the side of the moon we always see.– It’s got virtually no maria and a whole bunch

of craters.• Key: Any region of a celestial body having

a lot of craters means that area is relatively old.– This is because young surfaces haven’t had

time to get so many craters.– Earth has few craters because we have

shifting tectonic plates and fresh soil.• And speaking of craters…

http://csep10.phys.utk.edu/astr161/lect/moon/luna.gif

1. The Near Side and the Far SidePhotographed by the Clementine Spacecraft in 1994

http://astrobites.org/wp-content/uploads/2014/06/NearAndFarMoonWiki.pngs

Near Side Far Side

1. General Lunar CharacteristicsCraters and the Surface

• Many of the craters we can see have been named after famous astronomers.– One of the most prominent is Tycho, named after Tycho

Brahe. It’s the big one in the image below.• See those faint “lines” running from it?

http://upload.wikimedia.org/wikipedia/commons/6/6b/Tycho_Crater.jpg

1. General Lunar CharacteristicsCraters and the Surface

• Those faint lines coming from the crater are the rays, made of ejecta from that meteor impact.

• Other surface features include rilles, which are grooves in the surface in which lava once flowed.

http://upload.wikimedia.org/wikipedia/commons/6/6b/Tycho_Crater.jpg

http://upload.wikimedia.org/wikipedia/commons/thumb/

6/61/Moon_names.svg/2000px-Moon_names.svg.png

2. Lunar Gravity EffectsTides

• Tides are caused by the Moon’s gravity as it tugs on the water on Earth.– The water on Earth “bulges” in two spots – the side nearest the

Moon and the opposite side (due to inertia).– Two tides occur each day (high tide and low tide).

• Tides vary periodically as, on occasion, the Moon and the Sun combine to exert a lot of gravitational force on water.– The spring tide.

• Sometimes, the Moon and Sun exert less-than-normal pulls on water because they’re at right angles to one another and cancel out each other’s gravity.– The neap tide.

2. Lunar Gravity EffectsDaily Tides

• Note that we are rotated into the tidal bulge, which remains constant.

http://kgortney.pbworks.com/f/1241198825/Tide-Animation.gif

2. Lunar Gravity EffectsSpring/Neap Tides

http://home.hiwaay.net/~krcool/Astro/moon/moontides/

SUN

For more…

• UniverseToday – How Do The Tides Work

3. Lunar Rotation/Revolution EffectsLunar Elliptical Orbit

• Like Earth, the Moon also has an elliptical orbit.– Also like Earth (and the other planets), the Moon

revolves counterclockwise around the Earth.• You remember how perihelion is when the Earth is

closest to the Sun?– Perigee is when the Moon is closest to the Earth.

• You remember how aphelion is when the Earth is farthest from the Sun?– Apogee is when the Moon is furthest from the Earth.

3. Lunar Rotation/Revolution EffectsLibrations

• Even though we only see one side of the Moon, it wobbles enough that we actually get to see 59% of it.– There are a number of different

“wobbles” and explanations for that 59%, but in short they’re all known as librations.• The “up and down” rocking is a result of

the moon’s ecliptic being inclined relative to Earth’s orbital plane.

• The “side to side” rocking is a result of the moon’s elliptical orbit and variable orbit speed.

Aside: Libra Weight?

http://i.space.com/images/i/000/029/891/i02/libra.jpg?1371505868http://www-spof.gsfc.nasa.gov/stargaze/Smoon4.htm

• Libra, a star sign and a constellation, comes from the Latin for “scale.”

• “Libra” also used to be the word used for “pounds,” as in the unit of weight.– Ever wonder why “pounds” is

abbreviated “lbs?” Now you know.• Just the way old-timey scales

might oscillate, the Moon’s movements were also called librations.

Precession

• One quick thing while we’re on the topic of wobbling.

• While not as much or as quickly as the Moon, the Earth wobbles slightly on its axis, a movement caused by the Moon.– This is called precession, and it takes 26,000 years to

complete a cycle.– It’s like seeing a top that’s soon going to stop

spinning.

Aside: Milankovitch Cycles• Precession is one of three components of

something collectively known as Milankovitch Cycles, named for astronomer Milutin Milankovitch.

• The other two components are:– Axial Tilt

• The tilt of the Earth on its axis; varies between 22.1° and 24.5°.

– Eccentricity• The Earth’s orbit varies between nearly perfectly

circular and kinda elliptical as a result of the gravity of Jupiter/Saturn and other planets.

"Milutin Milanković" by Unknown - http://www.sanu.ac.rs/. Licensed under Public Domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Milutin_Milankovi%C4%87.jpg#/media/File:Milutin_Milankovi%C4%87.jpg

Milutin Milankovitch(1879-1958)

Aside: Milankovitch Cycles• Milankovitch Cycles are often cited by deniers of climate

change as a reason why climate change is not anthropogenic (human-caused).

• In fact, they do correlate with significant shifts in Earth’s climate.

• There’s just one problem in using them to explain the recent changes in temperature:– Precession cycles take 26,000 years.– Axial tilt cycles take 41,000 years.– Eccentricity cycles take 100,000 years.

• Sorry guys, believe it or not, climate change is still reality.

Milankovitch Cycles and Climate Change

http://upload.wikimedia.org/wikipedia/commons/7/7e/Milankovitch_Variations.png

Back to the Phases of the Moon

• There are some vocabulary words associated with the moon phases:– Waxing means the visible part of the Moon is getting larger.– Waning means the visible part of the Moon is getting

smaller.– Gibbous means the Moon is nearly full (whether waxing or

waning).• Key: The moon phases “move” right to left (backward

reading direction).– You may want to sketch these…

Moon Invisible

FromEarth

Moon Phases: Why?

• What causes the shadows and lights across the Moon?– Yep, it’s the positioning of the Sun and the Moon

relative to Earth.

SUN

Moon Invisible

FromEarth

Synodic versus Sidereal Months

• Months are named for moon movements.• A sidereal month is like a sidereal day.– The movement of the Moon around the Earth 360°.– Key: It takes 27.3 days.

• A synodic month is like a synodic/solar day.– The time it takes to go from new moon to new

moon.– Key: It takes 29.5 days and needs to revolve 390°

to do that, not 360°.• Why?

Synodic versus Sidereal Months

• Remember, in 27.3 days the Moon has completed 360° (synodic month).– However, in that time, the Earth travels a little under

30° around the Sun.• So the Moon needs to “catch up” in order to get

in the right location to be a new moon again.– That takes another 2.2 days, totaling 29.5 days and

390°.

Synodic versus Sidereal Months

Lunar Phases

• Lunar Phases Interactive• Lunar Phases worksheet

The Moon

• So, uh, it turns out there’s a whole lot of people that actually believe NASA faked the moon landing.– Crazy, right?

• The skepticism boiled over in 2001 when FOX (surprise) aired a show called Conspiracy Theory: Did We Land on the Moon?

• As you might guess, all the “theories” presented can be refuted…but let’s give ‘em a fair shake anyway.– First we’ll watch Conspiracy Theory.– Then we’ll watch two quick follow-up videos.– Then we’ll do a little of our own research to find the truth.– Then we’ll watch In the Shadow of the Moon for a counterpoint.

Follow-Up Videos

• Buzz Aldrin Punches Bart Sibrel• UniverseToday – How Do We Know the Moon

Landing Isn’t Fake• In the Shadow of the Moon – Were the Moon

Landings Faked• In the Shadow of the Moon– With video questions.

Just for fun…

http://pbfcomics.com/248/

4. Lunar (and Solar) Eclipses

• Hopefully by now you’ve gotten a sense for the weird dance thing the Moon and Earth are doing around the sun.– It takes three to celestially tango.

• As they move about one another, there are times when they “intersect” or align in special ways.

• You know these intersections better as…?– Eclipses! (both solar and lunar)• Not “of the heart…”

Let’s start with Lunar Eclipses.

• Before we fully understand all the terminology of eclipses, we need to know the names for shadows.– Yes, shadows.

• The Sun illuminates only part of Earth, causing the Earth to cast a two-part shadow.– The umbra is the main, darkest shadow.– The penumbra is on the edges of the umbra and

isn’t quite as dark.• Here’s what I mean…

¡Umbra y Penumbra!

• The penumbra is the partial shadow, while the umbra is the complete shadow.

• Fun fact: The umbra shadow is 500,000 miles long.

Penumbral Lunar Eclipse

• A penumbral lunar eclipse occurs if the Moon passes only through the penumbra (and none of the umbra).

Partial Lunar Eclipse

• A partial lunar eclipse occurs if the Moon passes through the penumbra and part-way into the umbra.

Total Lunar Eclipse

• A total lunar eclipse occurs if the Moon passes completely into the umbra.

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Wait a second…

• If the Moon revolves around the Earth each month, how come we don’t always see a lunar eclipse?– Well, first, the Moon must be in the “full moon” phase.– Then, the Moon’s orbit is not quite “level” with the

Earth’s.• It’s tilted about 5°, so it doesn’t always line up.

• Though it’s not really moving, the Sun appears to take a “path” through the celestial sphere.– That path is called the ecliptic, and for a lunar eclipse,

the Moon must cross into the ecliptic.• As in, must “intersect” with the plane of the Sun/Earth’s orbit.

Aside: Blood Moons

• Sometimes, during a total lunar eclipse, the moon may take on a reddish glow, known commonly as the blood moon.– This is caused by light

from the Sun passing through Earth’s atmosphere before illuminating the Moon.

Solar Eclipses• Lunar eclipses are more common than solar eclipses

because the Moon is moving into Earth’s relatively large shadow.

• On the other hand, solar eclipses are not nearly so common.– The Earth has to move into the relatively small shadow of the

Moon.• Like the Earth, the Moon also casts a shadow with an umbra

and penumbra.

Solar Eclipses

• Because of the size discrepancy between the Moon and Earth, there are 2.5 different kinds of solar eclipse:– Total Solar Eclipse– Partial Solar Eclipse– Annular Solar Eclipse

• Let’s take a look…

Total Solar Eclipse• A total solar eclipse occurs

in the region of Earth where the umbra “lands.”– The umbral shadow location

is known as the region of totality.

– As you might guess, the Moon’s shadow moves across the Earth.

– During an eclipse, things get quite eerily dark and you can see the corona (sun’s outer atmosphere).

Region of total solar

eclipse.

Region of partial solar eclipse.

Path of total

eclipse.

Total Solar Eclipse: August 11, 1999

Partial Solar Eclipse• A partial solar eclipse

occurs in the region of Earth just outside totality.– You may see the diamond

ring effect.

Region of total solar

eclipse.

Region of partial solar eclipse.

Path of total

eclipse.

http://www.dreamview.net/dv/new/photos/101917.jpg

Annular Solar Eclipse

• An annular solar eclipse occurs if the Moon’s umbra does not quite touch the ground.– Around the Moon is the

annulus or “ring of fire.”

Solar Eclipses

• Solar eclipses can make for very dramatic images, like this one:

From where would you see a total solar eclipse?

From where would you see a partial solar

eclipse?

Tell your neighbor… Partial Solar

Eclipse

Total Solar

Eclipse

Via Mir Space Station

Upcoming Solar Eclipses

Closure

• Eclipses Interactive• Eclipses of Moon and Sun worksheet– Note: If you’re confused about external/internal

tangent lines, see below.External tangent lines

are in white.

Internal tangent lines are in red.