Astronomy Unit 2Astronomy Unit 2

TelescopesTelescopesCelestial Spheres/ConstellationsCelestial Spheres/Constellations

Apparent Motion of the StarsApparent Motion of the StarsMotion of the PlanetsMotion of the Planets

TelescopesTelescopes Vocab Words for this section are:Vocab Words for this section are:

– Reflecting TelescopeReflecting Telescope– Refracting TelescopeRefracting Telescope– Radio TelescopeRadio Telescope– Space TelescopeSpace Telescope

TelescopesTelescopes Hans Lippershey was the inventor of Hans Lippershey was the inventor of

the telescope in 1608.the telescope in 1608. Galileo was the first to use a telescope Galileo was the first to use a telescope

to study the sky in 1609.to study the sky in 1609. The invention and use of the telescope The invention and use of the telescope

began a huge number of discoveries in began a huge number of discoveries in the field of astronomy.the field of astronomy.

TelescopesTelescopes 3 types of telescopes3 types of telescopes

– Optical Telescopes study visible light.Optical Telescopes study visible light. Reflecting telescopesReflecting telescopes use mirrors to bounce light from an use mirrors to bounce light from an

objective lens to an eyepiece lensobjective lens to an eyepiece lens Refracting telescopesRefracting telescopes use lens to bend light and magnify use lens to bend light and magnify

images coming through an objective lens.images coming through an objective lens.

– Radio TelescopesRadio Telescopes study radio waves from earth. study radio waves from earth.– Space TelescopesSpace Telescopes travel out of Earth’s atmosphere travel out of Earth’s atmosphere

to study the other types of radiation not visible to to study the other types of radiation not visible to the naked eye, and the radiation that cannot make the naked eye, and the radiation that cannot make it through earth’s protective atmosphere.it through earth’s protective atmosphere.

TelescopesTelescopes Optical Telescopes study the visible Optical Telescopes study the visible

light section of the electromagnetic light section of the electromagnetic spectrum.spectrum.

They uses mirrors and/or lenses to They uses mirrors and/or lenses to magnify the light.magnify the light.

TelescopesTelescopes One type of One type of

Optical Optical Telescope Telescope is the is the Reflecting Reflecting TelescopeTelescope– Within this Within this

telescope telescope there are there are mirrors to mirrors to bounce the bounce the light light traveling traveling through.through.

TelescopesTelescopes Another type Another type

of Optical of Optical telescopes is telescopes is the the Refracting Refracting TelescopeTelescope– Within this Within this

telescope telescope there are there are lenses to bend lenses to bend the light the light traveling traveling through.through.

TelescopesTelescopes Radio Radio

TelescopesTelescopes use a use a parabolic antenna parabolic antenna and a receiver to and a receiver to study radio study radio waves.waves.– Radio Waves Radio Waves

are a type of are a type of radiation that is radiation that is not normally not normally visible to the visible to the naked eye.naked eye.

TelescopesTelescopes Space Space

telescopestelescopes travel out of travel out of earth’s earth’s atmosphere to atmosphere to study all study all different types of different types of radiation that radiation that can not make it can not make it through earth’s through earth’s atmosphere.atmosphere.– Examples are Examples are

the Hubble the Hubble Space Space Telescope and Telescope and the Chandra the Chandra Space Space TelescopesTelescopes

Celestial Celestial Sphere/ConstellationsSphere/Constellations

Vocab words for this section are:Vocab words for this section are:– Celestial SphereCelestial Sphere– DeclinationDeclination– Right AscensionRight Ascension– ConstellationConstellation– Circumpolar ConstellationCircumpolar Constellation– North Circumpolar ConstellationNorth Circumpolar Constellation– South Circumpolar ConstellationSouth Circumpolar Constellation– ZodiacZodiac– EclipticEcliptic

Celestial Celestial Sphere/ConstellationsSphere/Constellations

A A celestial spherecelestial sphere is similar to a globe is similar to a globe of the sky.of the sky.– It is an imaginary It is an imaginary

sphere where the sphere where the sun, the moon, and sun, the moon, and all the other stars all the other stars appear to be appear to be combined.combined.

Celestial Celestial Sphere/ConstellationsSphere/Constellations

To locate on the To locate on the celestial sphere, you celestial sphere, you use declination and use declination and right ascension.right ascension.– DeclinationDeclination measures measures

angular distance North or angular distance North or South of the celestial South of the celestial equatorequator Between 0 and 90 Between 0 and 90

degreesdegrees– Right AscensionRight Ascension

measures distances measures distances eastward, along the eastward, along the celestial equator from celestial equator from the vernal equinoxthe vernal equinox Goes up to 360 degreesGoes up to 360 degrees

Celestial Celestial Sphere/ConstellationsSphere/Constellations

The 88 recognized constellations by The 88 recognized constellations by the International Astronomical Union the International Astronomical Union are plotted on the Celestial Sphere.are plotted on the Celestial Sphere.

Some constellations are close enough Some constellations are close enough to a celestial pole that they are visible to a celestial pole that they are visible in certain locations on earth all year in certain locations on earth all year long. These constellations are called long. These constellations are called Circumpolar ConstellationsCircumpolar Constellations..

Celestial Celestial Sphere/ConstellationsSphere/Constellations

Constellations close to the N. Celestial Pole Constellations close to the N. Celestial Pole are are North Circumpolar ConstellationsNorth Circumpolar Constellations– They are visible from the North Pole all year They are visible from the North Pole all year

long! long!

Constellations close to the S. Celestial Pole Constellations close to the S. Celestial Pole are are South Circumpolar Constellations.South Circumpolar Constellations.– They are visible from the South Pole all year They are visible from the South Pole all year

long!long!

Celestial Celestial Sphere/ConstellationsSphere/Constellations

These are These are the North the North Circumpolar Circumpolar ConstellationConstellationss

Celestial Celestial Sphere/ConstellationsSphere/Constellations

These are These are the South the South Circumpolar Circumpolar ConstellationConstellationss

Celestial Celestial Sphere/ConstellationsSphere/Constellations

The The eclipticecliptic is the apparent is the apparent path the sun traces out in path the sun traces out in the sky throughout the year. the sky throughout the year. – It is visible on the celestial It is visible on the celestial

sphere!sphere! Along the ecliptic there is a Along the ecliptic there is a

band of 12 constellations. band of 12 constellations. They are called the They are called the zodiac zodiac constellationsconstellations– These are where These are where

astrological signs come astrological signs come from. The constellation that from. The constellation that rises and sets during the rises and sets during the month of your birthday is month of your birthday is supposedly your “sign.”supposedly your “sign.”

Celestial Celestial Sphere/ConstellationsSphere/Constellations

The 12 constellations of the zodiac are:The 12 constellations of the zodiac are:

Apparent Motion of the Apparent Motion of the StarsStars

Vocab Words for this section are:Vocab Words for this section are:– ConstellationConstellation– Circumpolar ConstellationCircumpolar Constellation– Diurnal CirclesDiurnal Circles– ParallaxParallax

Apparent Motion of the Apparent Motion of the StarsStars

We have previously discussed We have previously discussed circumpolar constellations.circumpolar constellations.– This concept deals with how stars appear This concept deals with how stars appear

to move throughout the year.to move throughout the year.

Apparent Motion of the Apparent Motion of the StarsStars

If you trace the path a star makes If you trace the path a star makes each day, it would trace out a Diurnal each day, it would trace out a Diurnal Circle.Circle.– This the circular path a star appears to This the circular path a star appears to

take each day.take each day. We can’t see stars during the daytime We can’t see stars during the daytime

because of the sun, so we don’t actually see because of the sun, so we don’t actually see the circle.the circle.

Apparent Motion of the Apparent Motion of the StarsStarsDiurnal CirclesDiurnal Circles

Apparent Motion of the Apparent Motion of the StarsStars

Stars also display Stars also display parallaxparallax..– ParallaxParallax is the apparent movement of an object is the apparent movement of an object

due a change in the viewer’s position.due a change in the viewer’s position.– You can try it with your finger.You can try it with your finger.

Hold your finger in front of your face. Close your left Hold your finger in front of your face. Close your left and view your finger from your right eye. Quickly switch and view your finger from your right eye. Quickly switch eyes. Go back and forth a few times. Your finger should eyes. Go back and forth a few times. Your finger should appear to move even though it isn’t actually moving.appear to move even though it isn’t actually moving.

As the earth moves around the sun, it As the earth moves around the sun, it changes our viewing position of stars. This changes our viewing position of stars. This causes them to display parallax!causes them to display parallax!

Apparent Motion of the Apparent Motion of the StarsStars

We use a stars parallax (or apparent shift) We use a stars parallax (or apparent shift) relative to “fixed” background stars, to relative to “fixed” background stars, to determine the distance to stars.determine the distance to stars.

Stars that are further away display less of Stars that are further away display less of a parallax, than stars that are close to us.a parallax, than stars that are close to us.

Motion of the PlanetsMotion of the Planets Vocab Words for this section are:Vocab Words for this section are:

– Sidereal MotionSidereal Motion– ProgradePrograde– RetrogradeRetrograde– Kepler’s 1Kepler’s 1stst Law of Planetary Motion Law of Planetary Motion– Kepler’s 2Kepler’s 2ndnd Law of Planetary Motion Law of Planetary Motion– EllipseEllipse

Motion of the PlanetsMotion of the Planets A sidereal day actually A sidereal day actually

takes 23 hours, 56 takes 23 hours, 56 minutes and 4.09 secondsminutes and 4.09 seconds– This is the amount of time it This is the amount of time it

takes the earth to get back takes the earth to get back to the same location it was to the same location it was at previously.at previously.

– We don’t use this as a day We don’t use this as a day because the earth not only because the earth not only rotates, but it moves a little rotates, but it moves a little bit around the sun in its bit around the sun in its revolution during each revolution during each rotation. This is where we rotation. This is where we get the 24 hour day from.get the 24 hour day from.

Motion of the PlanetsMotion of the Planets As we watch planets move across the As we watch planets move across the

sky, they move relative to their sky, they move relative to their background “fixed” stars.background “fixed” stars.– Planets normally move westward across the Planets normally move westward across the

night sky. This is called night sky. This is called ProgradePrograde motion.motion.– Sometimes planets appear to begin moving Sometimes planets appear to begin moving

“backward” or eastward across the night “backward” or eastward across the night sky. This is called sky. This is called RetrogradeRetrograde motion. motion.

Please not that if you look these words up, the directions will be backwards Please not that if you look these words up, the directions will be backwards because Astronomers pretend like you are living on the planet looking out. because Astronomers pretend like you are living on the planet looking out. For our purposes we define the word as how it looks in the night sky! For our purposes we define the word as how it looks in the night sky!

Motion of the PlanetsMotion of the Planets The planets don’t actually switch directions.The planets don’t actually switch directions.

– What is happening is our orbits around the sun What is happening is our orbits around the sun (the earth’s and whichever planet we are looking (the earth’s and whichever planet we are looking at) are catching up with each other. at) are catching up with each other.

– This makes the planet appear to move This makes the planet appear to move backwards for a small portion of time.backwards for a small portion of time.

See the animation at the following website See the animation at the following website to help you understand prograde vs. to help you understand prograde vs. retrograde motion:retrograde motion:

ProgradePrograde vs. Retrograde Motion vs. Retrograde Motion

Motion of the PlanetsMotion of the Planets Johannes Kepler developed 3 laws for Johannes Kepler developed 3 laws for

how the planets move around the sun. how the planets move around the sun. He did this after making detailed He did this after making detailed studies and observations as to how the studies and observations as to how the planets are moving. planets are moving. – We are going to study the first 2!We are going to study the first 2!

These laws don’t only apply to planets, These laws don’t only apply to planets, but they also apply to how moons orbit but they also apply to how moons orbit their parent planets!their parent planets!

Kepler’s First Law of Planetary MotionPlanets follow elliptical orbits, with the Sun at one focus of the ellipse.

Motion of the PlanetsMotion of the Planets

Motion of the PlanetsMotion of the Planets The planets move The planets move

around the sun in around the sun in an elliptical shape an elliptical shape with the sun at one with the sun at one of the foci.of the foci.– An An ellipseellipse appears appears

as a squashed as a squashed circle.circle. It is defined as a It is defined as a

closed loop where closed loop where the sum of the the sum of the distances from 2 distances from 2 points (the foci) to points (the foci) to every point on the every point on the line is constant.line is constant.

Motion of the PlanetsMotion of the Planets This means there are times throughout This means there are times throughout

the year where the earth is closer and the year where the earth is closer and further from the sun.further from the sun.– The earth is actually closer to the sun in The earth is actually closer to the sun in

December, our winter!December, our winter! It is about 147,450,000 km from the sunIt is about 147,450,000 km from the sun

– The earth is further from the sun in June, The earth is further from the sun in June, our summer!our summer! It is about 152,400,000 km from the sunIt is about 152,400,000 km from the sun

Kepler’s 2nd Law of Planetary Motion

As a planet moves in its orbit, it sweeps out an equal amount of area in an equal amount of time.

Motion of the PlanetsMotion of the Planets

Motion of the PlanetsMotion of the Planets Kepler’s 2Kepler’s 2ndnd Law implies that when a Law implies that when a

satellite is closer to its parent object, it satellite is closer to its parent object, it actually travels faster than when it is actually travels faster than when it is further away!further away!– When we are closer to the sun we travel When we are closer to the sun we travel

slightly faster than when we are further slightly faster than when we are further away.away.

– This is due to the gravitational pull the This is due to the gravitational pull the parent object has on the satellite.parent object has on the satellite. The pull the sun has on the earthThe pull the sun has on the earth

– On average the earth travels at 29.78 km/sOn average the earth travels at 29.78 km/s

Motion of the PlanetsMotion of the Planets Kepler’s Laws apply to ALL the planets Kepler’s Laws apply to ALL the planets

that orbit the sun.that orbit the sun. Kepler’s Laws also apply to how every Kepler’s Laws also apply to how every

moon orbits its parent planet!moon orbits its parent planet!