Astronomy Basics Where is it? How to see it? Angular positions in the sky How far is it? How to see it? Telescopes

Positions on the Celestial Sphere How to locate (and track) objects from a spinning, orbiting platform in space….

Positions on the Celestial Sphere The Altitude-Azimuth Coordinate System Coordinate system based on observers local horizon Zenith - point directly above the observer North - direction to north celestial pole NCP projected onto the plane tangent to the earth at the observer’s location h: altitude - angle measured from the horizon to the object along a great circle that passes the object and the zenith z: zenith distance - is the angle measured from the zenith to the object z+h=90 A: azimuth - is the angle measured along the horizon eastward from north to the great circle used for the measure of the altitude

Changes in the Sky Coordinates continuously changing in alt-az system for all celestial objects (except geo-stationary satellites) Earth’s rotation Earth’s orbit about Sun Proper motion of objects The moon Planets Asteroids Comets Satellites…. Milky Way From Frisco Peak. Paul Ricketts 

Motion of Stars about NCP

Earth’s Rotation Earth’s rotation is responsible for the “rapid” motion of objects through the sky Mud springs point 2 hour exposure of NCP. Paul Ricketts

Tilt of Earth’s Axis Position of sun, moon and planets on celestial sphere significantly influenced by the tilt of Earth’s axis. Stars far enough away that seasonal variation of position on celestial sphere not significantly influenced by the tilt of Earth’s axis… On timescale of thousands of years, however, position of even stars move on celestial sphere due to precession!!!!

Earth’s Orbit about the Sun Due to the Earth’s motion about the Sun : Line of sight to the sun sweeps through the constellations. The sun apparently moves through the constellations of the zodiac along a path known as the Ecliptic The constellations that are visible each night at the same time changes with the season A given star will rise approximately 4 minutes earlier each day The Ecliptic.The path of the sun through the year in equatorial coordinates.

Equatorial Coordinate System Coordinate system that results in nearly constant values for the positions of distant celestial objects. Based on latitude-longitude coordinate system for the Earth. Declination - coordinate on celestial sphere analogous to latitude and is measured in degrees north or south of the celestial equator Right Ascension - coordinate on celestial sphere analogous to longitude and is measured eastward along the celestial equator from the vernal equinox  to its intersection with the objects hour circle Hour circle

Positions on the Celestial Sphere The Equatorial Coordinate System Hour Angle - The angle between a celestial object’s hour circle and the observer’s meridian, measured in the direction of the object’s motion around the celestial sphere. Local Sidereal Time(LST) - the amount of time that has elapsed since the vernal equinox has last traversed the meridian. Right Ascension is typically measured in units of hours, minutes and seconds. 24 hours of RA would be equivalent to 360. Can tell your LST by using the known RA of an object on observer’s meridian Hour circle

What is a day? Solar day Sidereal day The period (sidereal) of earth’s revolution about the sun is 365.26 solar days. The earth moves about 1 around its orbit in 24 hours. Solar day Is defined as an average interval of 24 hours between meridian crossings of the Sun. The earth actually rotates about its axis by nearly 361 in one solar day. Sidereal day Time between consecutive meridian crossings of a given star. The earth rotates exactly 360 w.r.t the background stars in one sidereal day = 23h 56m 4s

Annalemma Position of sun at “noon” Mean (average) solar day is 24 hours Equation of time Position of sun at “noon”

Local Sidereal Time LST = 100.46 + 0.985647 * d + long + 15*UT d is the days from J2000, including the fraction of a day UT is the universal time in decimal hours long is your longitude in decimal degrees, East positive. Add or subtract multiples of 360 to bring LST in range 0 to 360 degrees.

Precession of the Equinoxes Precession is a slow wobble of the Earth’s rotation axis due to our planet’s nonspherical shape and its gravitational interaction with the Sun, Moon, etc… Precession period is 25,770 years, currently NCP is within 1 of Polaris. In 13,000 years it will be about 47 away from Polaris near Vega!!! A westward motion of the Vernal equinox of about 50” per year.

Celestial Coordinates Links… http://spiff.rit.edu/classes/phys445/lectures/radec/radec.html http://home.att.net/~srschmitt/script_celestial2horizon.html http://www.coyotegulch.com/articles/StellarCartography/na0002.html http://tycho.usno.navy.mil/sidereal.html http://www.jgiesen.de/elevaz/basics/astro/stposengl.htm http://idlastro.gsfc.nasa.gov/ http://idlastro.gsfc.nasa.gov/ftp/pro/astro/hor2eq.pro http://idlastro.gsfc.nasa.gov/ftp/pro/astro/eq2hor.pro

Distance and Brightness Stellar Parallax The Magnitude Scale

Stellar Parallax Trigonometric Parallax: Determine distance from “triangulation” Parallax Angle: One-half the maximum angular displacement due to the motion of Earth about the Sun (excluding proper motion) With p measured in radians

PARSEC/Light Year 1 radian = 57.2957795 = 206264.806” Using p” in units of arcsec we have: Astronomical Unit of distance: PARSEC = Parallax Second = pc 1pc = 2.06264806 x 105 AU The distance to a star whose parallax angle p=1” is 1pc. 1pc is the distance at which 1 AU subtends an angle of 1” Light year : 1 ly = 9.460730472 x 1015 m 1 pc = 3.2615638 ly Nearest star proxima centauri has a parallax angle of 0.77” Not measured until 1838 by Friedrich Wilhelm Bessel Hipparcos satellite measurement accuracy approaches 0.001” for over 118,000 stars. This corresponds to a a distance of only 1000 pc (only 1/8 of way to center of our galaxy) The planned Space Interferometry Mission will be able to determine parallax angles as small as 4 microarcsec = 0.000004”) leading to distance measurements of objects up to 250 kpc.

The Magnitude Scale Apparent Magnitude: How bright an object appears. Hipparchus invented a scale to describe how bright a star appeared in the sky. He gave the dimmest stars a magnitude 6 and the brightest magnitude 1. Wonderful … smaller number means “bigger” brightness!!! The human eye responds to brightness logarithmically. Turns out that a difference of 5 magnitudes on Hipparchus’ scale corresponds to a factor of 100 in brightness. Therefore a 1 magnitude difference corresponds to a brightness ratio of 1001/5=2.512. Nowadays can measure apparent brightness to an accuracy of 0.01 magnitudes and differences to 0.002 magnitudes Hipparchus’ scale extended to m=-26.83 for the Sun to approximately m=30 for the faintest object detectable

Flux, Luminosity and the Inverse Square Law Radiant flux F is the total amount of light energy of all wavelengths that crosses a unit area oriented perpendicular to the direction of the light’s travel per unit time…Joules/s=Watt Depends on the Intrinsic Luminosity (energy emitted per second) as well as the distance to the object Inverse Square Law:

Absolute Magnitude and Distance Modulus Absolute Magnitude, M: Defined to be the apparent magnitude a star would have if it were located at a distance of 10pc. Ratio of fluxes for objects of apparent magnitudes m1 and m2 . Taking logarithm of each side Distance Modulus: The connection between a star’s apparent magnitude, m , and absolute magnitude, M, and its distance, d, may be found by using the inverse square law and the equation that relates two magnitudes. Where F10 is the flux that would be received if the star were at a distance of 10 pc and d is the star’s distance measured in pc. Solving for d gives: The quantity m-M is a measure of the distance to a star and is called the star’s distance modulus

A Brief talk about Telescopes Types of Telescopes Refractor Reflector Newtonian Schmidt-Cassegrain …. What Does a Telescope Do? Light Collection Image Formation Pointing Go-To Telescopes

Types Refractor Reflector Catadioptric

Light Collection The aperture of the optical instrument allows light coming from a source to be collected for image formation. The larger the aperture the more light is collected, therby allowing dimmer objects to be seen. Meade LX200 14” diameter Human Eye 1/4” diameter 99,314 mm^2 126 mm^2 Our 14” Meade has 788 times larger area than your eye

Light Collection Magnitude limit of 14” scope Assume that the unaided eye can see down to 6th magnitude. The amount of light collected increases with light collection area 14” scope hase 788 times the area of your eye Magnitude Definition Each 5 magnitudes  100 times the light Each magnitude  =2.51 times the light With 14” scope should be able to see down to magnitude 13.24

Image Formation Lenses or Mirrors Focus light in such a way that the light rays emanating from one point on the object is focused to one point in the focal plane thereby forming an image of the object

Eyepieces and Magnification Need eyepiece to examine image Magnification = Primary Focal Length ----------------------------- Eyepiece Focal Length

Resolution The ability to make out detail of an object Separate binary stars See features on extended objects Diffraction limit Maximum useful magnification

Focal Ratio Focal Length/Aperture “Speed/Brightness” of optics f/8 requires 4x exposure time of f/4 Field of View Smaller is faster and wider

Telescope Pointing Mount types Altitude-Azimuth Equatorial Fork German Equatorial Dobsonian

Altitude-Azimuth Mount

Equatorial Fork Mount

German Equatorial

Dobsonian Mount

Go-To Telescopes Alignment of Equatorial Mount Scopes Basic Setup Computer Location and Time Use of Catalogs Use of Coordintes Telescope Finderscope alignment Basic Usage Finding and Centering Objects Focusing

Warnings !!!!! Know the basic operation before turning on scope Be prepared to switch off/ stop scope from slewing Watch cables…..