INTRODUCTION TO ASTRONOMY Astronomy: is a science that studies everything outside Earth’s atmosphere such as planets, stars, asteroids, galaxies, and the properties and relationships of those celestial bodies. Brief intro

Astrology – the study of the movements and relative positions of celestial bodies interpreted as having an influence on human affairs and the natural world.

ASTROPHYSICS - the branch of astronomy concerned with the physical nature of stars and other celestial bodies, and the application of the laws and theories of physics to the interpretation of astronomical observations INTRO

Universe: the totality of all space, time, matter, and energy Expansive ---Massive----Large Universe -----Galaxy -----Solar system How Big

Milky Way is a Spiral Galaxy can Expand for 100,000 LY across What does this mean? Light Year = distance traveled by light in one year. One LY = about 9 trillion KM Rate: 300,000 KM/sec Sun’s light takes 8.3min to reach us Sun is 93 million miles away Video 2: light year explained

10 trillion kilometers 103 = 1,000 thousand 106 = 1,000,000 million 109 = 1,000,000,000 billion 1012 = 1,000,000,000,000 trillion If you were to count out 1,000 at a rate of 1number per second it would take 16min 1 million would take 2 weeks (16hrs per day) 1 billion = 50 years Video 2: How big is the universe

How “big” is the Earth? TINY?

Celestial Sphere Celestial sphere – imaginary sphere surrounding Earth to which objects in the sky were once considered attached animation of sphere

Constellations appear to move across sky from east to west (88 constellations) Polaris – North Star Axis for which the celestial sphere rotates Video 3 Constellations

Constellations today???

Zodiac - 12 constellations which the sun passes as it moves along ecliptic – that is, the constellations we would see looking in the direction of the sun if they weren’t overwhelmed by the sun’s light

Celestial coordinates Latitude= declination – degrees N and S of celestial equator (o) Longitude= right ascension – measured in angular units called hours, minutes, and seconds starting point is the sun

Video 4 The Universe - beyond the Big Bang - 85 min Beyond

Earth’s Orbital Motion Time is measured by the Sun Sunrise to sunset = 24 hour solar day Diurnal motion - apparent daily progress of sun and stars across sky diurnal motion

Sidereal day – day measured by stars, celestial sphere shifts daily causing day measured by stars different from a day measured by earth’s rotation solar vs sidereal

Reason for difference between days Earth moves with two motions simultaneously – Rotation & Revolution Rotates on its central axis while at the same time revolves around sun Noon on one day is slightly later at noon the next day

Seasonal changes Earth revolves 1 degree per day. Every few months we see different group of stars and constellations. Ecliptic – apparent motion of the sun the sky traces out on a celestial sphere

Solstices Northern Hemisphere’s summer: Earth’s axis is pointed toward the sun

June 21- Summer Solstice, longest day of the year

Northern Hemisphere Winter: Earth’s axis is pointed away from sun

Winter Solstice December 21 - Shortest day in Northern Hemisphere

Equinoxes Autumnal and Vernal Equinox for Northern hemisphere occur when north axis is not pointed away or toward the sun

Reason for Seasons Revolution Parallelism 23.5 degree Earth’s tilt Bill Season

Earth’s Long Term orbital changes Sidereal year – time required for Earth to complete exactly one orbit around the Sun, relative to the stars One Sidereal Year = 365.256 solar days long 20 minutes longer than tropical year Tropical year – interval of time from one vernal equinox to next = 365.242 solar days

Difference between tropical and sidereal year Precession – earth's axis changed direction over time caused by gravitational pull of moon and sun. Precession

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