Space, Earth and Space, Earth and Celestial ObjectsCelestial Objects

© Lisa Michalek

Celestial ObjectsCelestial Objects

The sun, moon, planets, stars or any distant The sun, moon, planets, stars or any distant object visible in the sky, generally appear to object visible in the sky, generally appear to rise in the east and set in the west.rise in the east and set in the west.Most appear to move along circular Most appear to move along circular

or curved paths.or curved paths.The motion occurs The motion occurs

at an angular rate at an angular rate of 15° per hour of 15° per hour (360° in 24 hours).(360° in 24 hours).

Motion of Stars and PlanetsMotion of Stars and Planets

Stars located over Earth’s equator follow nearly Stars located over Earth’s equator follow nearly the same path as the sun.the same path as the sun.

Stars in the southern portion of the sky briefly arc Stars in the southern portion of the sky briefly arc across or appear over the horizon.across or appear over the horizon.

Stars over the North Stars over the North Pole move in circles Pole move in circles around Polaris.around Polaris.

In addition to their In addition to their circular motion, planets circular motion, planets change their positions change their positions from night to night.from night to night.

ConstellationsConstellations

Although the stars are randomly distributed Although the stars are randomly distributed throughout the sky, ancient people imagined throughout the sky, ancient people imagined they saw patterns among them.they saw patterns among them.

These patterns were often associated with These patterns were often associated with traditions and legends that were part of the traditions and legends that were part of the culture of early civilizations.culture of early civilizations.Some were said to resemble people, animals, Some were said to resemble people, animals,

or objects.or objects.

ConstellationsConstellations

Regions in the Night SkyRegions in the Night Sky

Astronomers have divided the night sky into Astronomers have divided the night sky into 88 regions.88 regions.

Each region is associated with a Each region is associated with a constellation.constellation.

Night Sky ModelsNight Sky Models

Early civilizations considered Earth to be a Early civilizations considered Earth to be a stationary object located at the center of stationary object located at the center of the universe.the universe.This was because they could not This was because they could not

feel the Earth moving.feel the Earth moving.This early model of This early model of

the universe was the universe was geocentricgeocentric, or , or Earth-centered.Earth-centered.

Heliocentric ModelHeliocentric ModelWhen the paths of the planets were When the paths of the planets were

carefully measured by astronomers, carefully measured by astronomers, some of the planetary motions were too some of the planetary motions were too complex and hard to explain.complex and hard to explain.

Therefore astronomers Therefore astronomers support this more support this more simple model.simple model.

This model includes This model includes all known planets all known planets revolving around revolving around the sun.the sun.

Heliocentric ModelHeliocentric ModelIncludes two motions of planet Earth.Includes two motions of planet Earth.

Each day Earth spins on Each day Earth spins on its its axisaxis is known as is known as rotationrotation..From west to east at the rate of From west to east at the rate of

15° per hour (360° in 24 hours).15° per hour (360° in 24 hours).Earth also orbits the sun once Earth also orbits the sun once

per year known as per year known as revolutionrevolution..The earth takes 365 ¼ The earth takes 365 ¼

days to revolve around days to revolve around the sun.the sun.

About 1° per day.About 1° per day.

Foucault PendulumFoucault Pendulum In 1851 the French scientist Jean Foucault In 1851 the French scientist Jean Foucault

suspended a long pendulum and set it swinging suspended a long pendulum and set it swinging along a north-south line.along a north-south line.

The Foucault Pendulum, mounted on a high The Foucault Pendulum, mounted on a high support, is able to move in any direction.support, is able to move in any direction.

Foucault observed how the Foucault observed how the pendulum appeared to change pendulum appeared to change direction as it swung freely in direction as it swung freely in a clockwise direction.a clockwise direction.

He interpreted this motion He interpreted this motion as the rotation of Earth as the rotation of Earth under the pendulum.under the pendulum.

Coriolis EffectCoriolis Effect

Winds blowing out of a high-pressure Winds blowing out of a high-pressure system always curve to the right in the system always curve to the right in the Northern Hemisphere.Northern Hemisphere.

The system of prevailing winds of Earth The system of prevailing winds of Earth forms a series of symmetrical bands located forms a series of symmetrical bands located north and south of the equator.north and south of the equator.

The Coriolis effect is the The Coriolis effect is the result of inertia acting on result of inertia acting on a rotating planet.a rotating planet.

Motions of the SunMotions of the Sun

Before there were mechanical clocks, the Before there were mechanical clocks, the movement of the sun through the sky was movement of the sun through the sky was used to track the passage of time.used to track the passage of time.

Sundials were among the first timekeeping Sundials were among the first timekeeping devices used by humans.devices used by humans.

A sundial reveals the A sundial reveals the passage of the daylight passage of the daylight hours as the shadow hours as the shadow of a stick (gnomon) of a stick (gnomon) shifts across a marked shifts across a marked dial or scale.dial or scale.

Motions of the SunMotions of the Sun

Our system of time is based upon the Our system of time is based upon the apparent motionsapparent motions of the sun. of the sun.The motions of celestial objects through the sky The motions of celestial objects through the sky

is called is called apparent motionapparent motion because the object is because the object is not really moving as it appears to be.not really moving as it appears to be.

The apparent rising and setting of the sun is The apparent rising and setting of the sun is actually caused by Earth’s rotation.actually caused by Earth’s rotation.

The The apparent solar dayapparent solar day is the interval of is the interval of time during which the sun passes from its time during which the sun passes from its highest point on one day to its highest point highest point on one day to its highest point on the next.on the next.

SeasonsSeasonsBecause Earth moves in its orbit, the sun’s Because Earth moves in its orbit, the sun’s

pathway from east to west in the sky also pathway from east to west in the sky also changes on a yearly cycle.changes on a yearly cycle.

At the At the autumnal equinoxautumnal equinox (about Sept 23), (about Sept 23), the sun rises due east and sets due west.the sun rises due east and sets due west.Daylight lasts for 12 hours, and it is the Daylight lasts for 12 hours, and it is the

beginning of fall, or autumn, in the Northern beginning of fall, or autumn, in the Northern Hemisphere.Hemisphere.

At the beginning of winter, the At the beginning of winter, the winter winter solsticesolstice (about Dec 21),the sun rises south (about Dec 21),the sun rises south of due east.of due east.This is the shortest daylight period of the yearThis is the shortest daylight period of the year ..

SeasonsSeasons

At the At the vernal equinoxvernal equinox (about March 21), the (about March 21), the sun rises exactly in the east and sets due sun rises exactly in the east and sets due west.west.The daylight period is 12 hours long, and it is the The daylight period is 12 hours long, and it is the

beginning of spring in the Northern Hemisphere.beginning of spring in the Northern Hemisphere.When the When the summer solsticesummer solstice (about June 21), (about June 21),

arrives the sun rises north of due east.arrives the sun rises north of due east.The summer solstice is the longest daylight The summer solstice is the longest daylight

period of the year; it is the beginning of summer.period of the year; it is the beginning of summer.

SeasonsSeasons

Autumnal Equinox Autumnal Equinox Fall in the Northern hemisphere.Fall in the Northern hemisphere.

Notice the amount of light and dark are equal in Notice the amount of light and dark are equal in both hemispheres.both hemispheres.

Winter SolsticeWinter Solstice   Winter in the Northern hemisphere.Winter in the Northern hemisphere.

Notice the North is getting much less daylight.Notice the North is getting much less daylight.Above the Arctic circle is in 24 hour darkness.Above the Arctic circle is in 24 hour darkness.

Vernal Equinox Vernal Equinox 

Spring in the Northern hemisphere.Spring in the Northern hemisphere.Both hemispheres are again getting the same Both hemispheres are again getting the same

number of hours of daylight.number of hours of daylight. It is identical to the Autumnal Equinox.It is identical to the Autumnal Equinox.

Summer Solstice Summer Solstice Summer in the Northern hemisphere.Summer in the Northern hemisphere.

Notice that the North is now getting many hours Notice that the North is now getting many hours of daylight and above the Arctic circle is in 24 of daylight and above the Arctic circle is in 24 hour daylight.hour daylight.

Latitude and the Angle of the SunLatitude and the Angle of the Sun

The path of the sun through the sky depends The path of the sun through the sky depends upon where you are when you observe it.upon where you are when you observe it.

As you travel northward from any mid-latitude As you travel northward from any mid-latitude location, the noon sun will move lower and location, the noon sun will move lower and lower in the sky.lower in the sky.

Observers at the poles see six months of Observers at the poles see six months of daylight, followed by six months of darkness daylight, followed by six months of darkness in a yearly cycle.in a yearly cycle.This is caused by a combination of the 23½° tilt This is caused by a combination of the 23½° tilt

of Earth’s axis and our revolution around the sun.of Earth’s axis and our revolution around the sun.

Earth’s AxisEarth’s Axis

Daylight HoursDaylight Hours

At equinox, for all locations At equinox, for all locations (except the poles), daylight lasts 12 hours.(except the poles), daylight lasts 12 hours.

At the equator throughout the year, At the equator throughout the year, there are 12 hours of daylight and there are 12 hours of daylight and 12 hours of night.12 hours of night.

As you approach the poles, the amount of As you approach the poles, the amount of seasonal variation in the length of daylight seasonal variation in the length of daylight increases until a maximum six months of increases until a maximum six months of daylight and six months of darkness is daylight and six months of darkness is reached at the North or South Pole.reached at the North or South Pole.

Daylight HoursDaylight Hours