Cosmic Distances Space Academy for Educators Summer 2012
Basics of Astronomy • The basic unit of measurement for dealing with distances inside our solar system is called an AU, or Astronomical Unit. This is the distance between the Earth and the Sun, roughly 92 million miles. It would take you 106 years to drive this distance in your car, if you went the speed limit, or over 3,536 years to walk that far, since there are few gas stations in space. • When dealing with objects outside our solar system the standard unit of measurement is the Light Year. This is the distance light travels in one year, roughly 6 trillion miles. • Scientists also use a unit of measurement called a Parsec, which is just over 19 trillion miles, or 3.26 light years.
Basics of Astronomy • The brightness of a celestial object is measured in “Apparent Magnitude”. This is not a true measure of how large or bright a star actually is, it is only how bright it appears when viewed from Earth. • Vega has replaced Polaris as the benchmark star for calculating apparent magnitude, because Polaris has been discovered to be three gravitationally bound stars, and changes brightness depending on their location.
Basics of Astronomy • Celestial bodies follow the same path taken by the Sun and Moon, rising in the East and setting in the West. • Celestial bodies are seasonal, only a select few are visible all year round. • Star patterns are called Asterisms.There are 88 asterisms recognized by the International Astronomical Union (IAU) in 1930 that are considered official Constellations. • Not all celestial bodies are stars!
What Else Is Out There? • Planetary Nebula: Cloud of gasses thrown off by dying stars • Dark Nebula: Clouds of gas and dust—site of star formation • Clusters: Thousands of new stars gravitationally bound together —they have absorbed the nebula that produced them • Galaxies:Stars in groups measuring hundreds of thousands of light years across —our own Milky Way is the closest example
Naming Astronomical Objects • Some objects have descriptive names based on their appearance or location:—the Orion Nebula, the Whirlpool Galaxy • Others are named after the person or observatory who first discovered and cataloged them: • Messier Objects (M113, etc.) are part of the Messier Catalogue started by Charles Messier as he searched for comets in 1771 and noted fuzzy, non-star objects. • New General Catalogue (NGC) objects were compiled in the 1880’s by the Royal Astronomical Society. • The Caldwell Catalogue was compiled by Sir Patrick Moore as a companion to the Messier Catalogue and contains the work of many independent amateur astronomers.
Naming Astronomical Objects • Many stars are still called by their traditional Greek, Roman or Arabic names. —examples: Rigel, Sirius, and Bellatrix • Stars are also named with a Greek prefix according to their constellation and order of their apparent magnitude. —RigilKentaurus (“foot of the centaur”) is better known as Alpha Centauri (α Centauri) since it is the brightest star in the constellation Centaurus. • Stars in a binary system are named with a suffix denoting order of brightness. —RigilKentaurus is also a triple star, named Alpha Centauri A, Alpha Centauri B, and Alpha Centauri C.
Finding Your Bearings • In the absence of a compass you can easily find North using the stars. • There are five circumpolar constellations—visible year round, they circle Polaris (the North Star). • Ursa Major (“Big Dipper”) • Ursa Minor (“Little Dipper”) • Cassiopeia (“the Queen,” the big “W”) • Cepheus (“the King”) • Draco (“the Dragon”)
Finding Your Bearings • Polaris is the end star in the handle of “the Little Dipper,” Ursa Minor. • Once you find Polaris you can locate other celestial bodies by knowing their degrees from the horizon. • When held at arms length your fist will cover roughly 10°. • For example, 25° from SW horizon will be 2½ fists high.
Circumpolar Constellations: Ursa Minor
Circumpolar Constellations: Ursa Minor Once thought to be a Binary star, new images from the Hubble telescope have confirmed that Polaris is actually a triple star. Polaris Ab is the most recently discovered star in the system, since Polaris B was already a well known and documented star Astronomers gave it the designation Ab to put it ahead of Polaris B in order of brightness and avoid confusion by renaming Polaris B.
Cosmic Distance Activity • The purpose of this activity is to create a three dimensional representation of a constellation. This will not only show how the stars appear from Earth, but also shows the depth of the star field. • For this activity you will need constellation charts, distances of the stars in the constellation, and a list of apparent magnitudes of the stars in the constellation. • Materials for this activity are cardboard, string, rulers and foam balls of various sizes to represent apparent magnitudes of stars. • Remember, X is your width, Y is your height, Z is your depth!
Cosmic Distance ActivityGraphing Your Constellation • Step 1: Make 10 marks 1 cm apart across the top of your constellation image. Label this your X axis. (Center your marks over the star field, do not start at the top left corner.) • Step 2: At the 0 mark of your X axis begin labeling down, making marks at 1 cm intervals. (You may have more than 10 marks.) • Step 3: Find the co-ordinates for each star in your constellation, and multiple your answers by 3. (A star at 1,4 becomes 3,12) • Step 4: Measure and label the top of your cardboard sheet with marks 3 cm apart. Label this your X axis.
Cosmic Distance ActivityGraphing Your Constellation • Step 5: Measure and mark the left side of your cardboard at 3 cm intervals and label this your Z axis. To find the Z axis’ unit of measurement identify the star in your constellation with the farthest distance from the Sun in light years, and divide that distance by 10. Starting with 0 in the top left corner, label the left side of your graph with this new unit. (ex. 350 light years / 10 = 35, so from the top left corner down is 0,35,70,105,140, 175, 210, 245, 280, 315, and 350 in the bottom left corner.) • Step 6: Using the Brightness chart retrieve foam balls from the box corrosponding to the magnitude of the stars. (0-1 mag = biggest ball, 1.01-2 = next biggest ball, ect.)
Cosmic Distance ActivityGraphing Your Constellation • Step 7: Tie one end of your roll of string to the eyelet on your foam ball, measure out the distance recorded as the Y axis for each star. Leave a little extra string to accommodate your tape. • Using your X axis calculations and distance as your Z axis begin hanging your foam spheres from the cardboard. • From the X axis end you can see the constellation as it appears from Earth, but if you turn it sideways it shows the actual immensity of space. • Our model is small today, but this activity can be done on your classroom ceiling, or in the hallways outside your classroom to make a much larger star chart.