Alta High Astronomy

Intro: Astronomy

A stellar course to be in!

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Chapter 1: Charting the Heavens

The Foundations of Astronomy

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What is Astronomy?

Astronomy is the study of the Universe where the universe is the totality of all space.

Often when we think of astronomy, we look to the heavens and think of the constellations.

Constellations are groups of stars which have been given names and that when viewed with some imagination, resemble a known object.

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Constellations Constellations are the result of the natural

human tendency to look for patterns. The stars that make up a constellation are not

necessarily close to each other in space, they are simply bright enough to be seen by the naked eye.

Constellations usually have a cultural bias, that is that each culture throughout history has assigned a name and a story to the constellations. For example, the constellation which North Americans refer to as the big dipper is know as the wagon or the plough in Europe.

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Constellations in the Sky:Orion

Orion – also know as the hunter is the predominant constellation in the winter sky in the northern hemisphere.

Usually located by the three stars in the “belt”

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Constellations in the Sky:Orion

Astersim A distinctive

pattern of stars that forms part of one or more constellations

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Objectives Explain the concept of the celestial sphere Understand and use angular measurements

including RA and DEC to locate objects in the sky

Describe how celestial objects appear to move in the sky and account for these apparent motions in terms of the actual motions of Earth

Understand the types of eclipses and how each occurs

Use simple geometry to measure the distances and sizes of faraway objects.

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Finding Your Way Around the Earth

On the Earth we give directions using lines of longitude called meridians

These lines begin at 0° (Prime Meridian) and go 180° (International date line) east or west

Lines of latitude which are called parallels.

These lines begin at the equator (0°) and measure to 90° North or South (North and South Pole)

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Finding Your Way Around the Earth

Red dot is in Galveston, TX Latitude 29° 43’ North Longitude 94º 48’ West

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Finding Your Way Around the Sky

In the Sky, we use a concept called the Celestial Sphere to locate objects.

Here we use degrees of Declination (similar to latitude) to tell an object’s position above or below the Celestial Equator

Hours of Right Ascension (similar to longitude) to tell its position east or west of the.

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Measurement in the Sky A circle contains 360° so when an

object rotates on its axis (as the earth does) it is said to move through 360°

Since the earth rotates once every 24 hours, it rotates 15° per hour.

1 degree = 60’ or 60 arcminutes 1’ = 60” or 60 arcseconds Finally, 1 hour of RA = 15°

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Motion in the Sky The apparent motion of the stars in the sky

(including our own sun) is a result of the earth’s rotation, in combination with its revolution around the sun

The time required for the earth to rotate on its axis is known as a solar day

However, because the earth also is revolving while it rotates the position of the stars at the end of the solar day is slightly different each night

The time required to bring the stars back to the same position as the previous night is known as a sidereal day

A solar day is 3.9 minutes longer than a sidereal day

Leap Year with its additional day each year, is our attempt to make our calendar match that of the stars

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The Annual Path of the Sun

As the sun travels across the sky during the year it follows a predictable path known as the ecliptic

The ecliptic passes through 12 identifiable constellations known as the constellations of the zodiac

A branch of pseudoscience which studies the zodiac and its supposed influence on our lives is astrology – which we will not study in this class

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The Annual Path of the Sun

The ecliptic is tilted 23.5° because that is the tilt of the earth with respect to the sun

The tilt of the ecliptic is what causes the seasons of the year and explains why the seasons in the northern hemisphere are reversed from those in the south

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The Seasons The northern most point

on the ecliptic is where the winter solstice occurs (Dec 21 – the shortest day of the year) and the southern most point is the summer solstice (June 21 – longest day of the year)

In between these points are the two points where the sun crosses the celestial equator, points of equal day and night called equinoxes (September 21 – Autumnal equinox & March 21 – Vernal or Spring equinox)

Seasons of the Northern Hemisphere

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Precession Over the long term, the

fact that the earth is tilted with respect to the sun causes a “wobble” known as precession

Precession will eventually cause a significant shift in the direction of the north pole of the celestial sphere shifting our “north star” from its current position pointing at Polaris to a new position pointing at Vega

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The Moon: Our Nearest Neighbor

The moon, like the stars goes through a regular cycle of changes

These changes are called phases

There are eight phases in the cycle

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Eclipses An eclipse is a blocking of light caused

by one celestial object passing into the shadow of another object

This occurs when the sun, moon, and earth line up

The two types of eclipses are a solar eclipse where the sun is blocked, and a lunar eclipse where the moon is blocked

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Solar Eclipse

A solar eclipse occurs at the new moon when the moon passes between the sun and the earth

In a perfect alignment there is a total shadow called the umbra producing a total eclipse

In a less than perfect alignment there is a partial shadow called the penumbra producing a partial eclipse

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Geometry: The Mathematics of Astronomy The ancient

astronomers were good mathematicians. Part of the reason the Greeks developed astronomy was to study the stars.

The measurement of distances is accomplished by triangulation or the use of a right triangle

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Triangulation To triangulate a distance

to an object you need to know the baseline, or a distance between two point on a straight line opposite the object

You also need to know the angle between the baseline and the object or any other angle in the triangle.

Of course the last criteria is that the angle between the baseline and the distance you want to measure must be 90°

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Stellar Parallax Stellar Parallax uses

triangulation combined with the apparent shifting of an object when seen from two points to estimate the distance to far away celestial objects

Using the diameter of the earth as a baseline, astronomers find the parallax angle by observing the same object from opposite sides of the earth

Then using triangulation they estimate the distance to the object.