LAB (Inst. Dickinson): Lab Constellation/Star Quiz Angular Measurement Lab Agenda LECTURE (Prof. Canales): Discuss Formal Lab Report on FOV- Due Tues 2/15 LAB PREP: Unit Conversion Review Dec. & RA and degree, minute second (Norton?) Arc length formula and small angle formula do fill in the blanks for Angular Measurement Lab. LECTURE: Scaling, Distance (parsec) Magnitudes (apparent and absolute) Tutorial: motion CS (3-4) LAB (Inst. Dickinson) Planetarium FYI Intro Moon Project & Journal Labs- Norton Coordinates and
Measuring Angular Size/Distance HOW BIG IS IT? WHERE DO I LOOK?
RADIAN - SEC CONVERSION Angle in degress = Angle in radians X 57.29 Angle in arcsec = Angle in radians X 206,265
Unit Conversion (if time)
Week 5 Motion of C.S., Scaling, Distances & Magnitude of Stars Earth s rotation causes the Sun, Planets, Moon and stars to appear to move (nightly/daily) when viewed from Earth
Will the North Celestial Pole (Earth s Northern Axis) always point toward Polaris? Currently it is within 1 degree of Polaris, but it will take thousands of years for our North Star to change to another star.
Daily Motion of the Stars (Sun, Moon, Stars & Planets) Do the human animation, neglect tilt of Earth! (blank paper with cardinal directions) Do stars (etc) rise above your Eastern or Western horizon? Does the moon rise later, earlier or at the same time each day?
Nightly Motion of the Stars Do we view the C.S. (Celestial Sphere) from above as this top arrow indicates? Celestial Sphere Rotation 1 Celestial Sphere 4 3 1 Star B 2 Star A 2 Celestial Sphere Does the C.S. appear to rotate CW or CCW as viewed by Earthlings? 4 Figure 2 3 Celestial Sphere Rotation Horizon
Nightly Motion (diurnal motion) of the Stars (in Northern Hemisphere) For stars (is similar for the Sun, Moon and planets) they first rise near the eastern horizon, move upward and toward the south, and then move down and set near the western horizon.
Nightly Motion of the Stars Looking North: Stars appear to move counter-clockwise around the stationary North Star (Polaris) we call these circumpolar stars.
Looking North: Circumpolar Stars Circumpolar stars seem to move counter-clockwise around the stationary North Star. These constellations and stars are visible any night of the year in the NORTHERN sky because they never rise or set! Examples: Ursa Major, Ursa Minor, Draco, Cepheus, and Cassiopeia
What happens over time in the Northern Sky?
What direction is the camera facing in this picture (HINT: see Tutorial book or next slide)
Nightly Motion of the Stars Do we view the C.S. (Celestial Sphere) from above as this top arrow indicates? Celestial Sphere Rotation 1 Celestial Sphere 4 3 1 Star B 2 Star A 2 Celestial Sphere Does the C.S. appear to rotate CW or CCW as viewed by Earthlings? 4 Figure 2 3 Celestial Sphere Rotation Horizon
Tutorial: Motion pg. 3-4 (SKIP pg. 5 & 6, but show SUN ) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. If you get really stuck or don t understand what the Lecture Tutorial is asking, ask your Professor to help.
Celestial Sphere Rotation North Star 4 Path of Star B 1 2 Celestial Sphere Path of Star A North Star 3 Earth s Equator Horizon At what time will Star B be located high in the Northwestern sky? A. 4:00 am B. 10:00 am C. 2:00 pm D. 7:00 pm E. 1:00 am 6 PM North Celestial Sphere Rotation
Celestial Sphere Rotation North Star 4 Path of Star B 1 2 Celestial Sphere Path of Star A North Star 3 Earth s Equator Horizon 6 PM North If you were able to see the motion of star B at Noon, over a period of 15 minutes what direction would it appear to move? A. west (to the left) B. east (to the right) C. South (out of the page) D. away from the horizon (up) Celestial Sphere Rotation E. toward the horizon (down) & east
If you could see stars during the day, the drawing below shows what the sky would look like at noon on a given day. The Sun is near the stars of the constellation Gemini. Near which constellation would you have expected the Sun to be located at sunrise Sun on this day? A. Leo B. Cancer C. Gemini D. Taurus E. Aries Leo East Cancer Gemini South Taurus West Aries 0/0
Thousands of km Astronomical Unit A few to about 1,000 Light-years 10,000 to 100,000 Light-years Millions of Light-years Billions of Light-years Parsec = 3.26 light years
Do all stars appear the same? How are they different? Which one looks the coolest? Hottest? Are they all the same brightness? Do they all look the same size?
the brightest star Sirius at -1.44. the brightest planet Venus varies in brightness and is about -4.4 magnitude at maximum brightness. the Moon is -12.7 magnitude at maximum brightness the Sun is -26.75 magnitude. As the Sun sets, some stars are visible. These are the first magnitude stars. Later, when twilight is over, more stars are visible. These are the second magnitude stars, and so on Is this apparent magnitude or absolute magnitude?
Two Kinds of Brightness Apparent Magnitude, m: How bright the object appears to us on Earth. Absolute Magnitude, M: How bright a star actually is, its intrinsic brightness. (determine a star s absolute brightness by imagining moving it to 10 pc away from the observer)
Apparent Magnitude is a number that represents the apparent brightness of stars as seen on Earth The larger the number the dimmer the object will appear from Earth Note we use the letter m for apparent magnitude
Apparent Magnitudes Which would look brighter? Sirius, m = -1.4 Venus, m = -4.4 Which would look brighter? Vega, m = 0.03 Antares, m = 1.06
Apparent Magnitudes Which would look brighter? Sirius, m = -1.4 Venus, m = -4.4 Which would look brighter? Vega, m = 0.03 Antares, m = 1.06
Smaller/negative numbers correspond to BRIGHTER stars and Bigger/positive numbers correspond to DIMMER stars
Why do stars in the night sky appear considerably different in brightness? The distance to stars are not all the same. Some stars are intrinsically brighter than others they simply give off more light.
Which star looks like it is giving off more light? But, which star is actually giving off more light?
How bright a star appears depends on both how much light it releases (its actual brightness or luminosity) and how far away it is (distance) according to the inverse square law
The Inverse Square Law apparent magnitude = m= Power or Luminosity (Watts) 2 Surface Area (in meters ) ( L) 4πd 2
Problem Rigel (m = 0.18) Spica (m = +1.0) Which looks brighter from Earth?
Rigel (m = 0.12) Spica (m = +1.0) Which looks brighter? Rigel BUT... It turns out that Spica actually gives off 1000 times more light than Rigel!! SO..If Spica is giving off more light, why would it appear dimmer in the sky here at Earth? ANSWER : Because Spica is much farther away from Earth than Rigel!
PROBLEM: Stars are at different distances from Earth and so it s hard to know which stars are ACTUALLY brighter versus which APPEAR brighter SOLUTION: We imagine having them all lined up together at the same distance (10 parsecs or 32 light years), then compare the brightness of each star
SOLUTION: We imagine having them all lined up together at the same distance (10 parsecs or 32 light years), then compare the brightness of each star (1 parsec = 206.26 10^3 AU = 3.26156 ly) This allows us to determine how bright the star actually is the Absolute Magnitude of the star - M
Absolute Magnitude M - compares the brightness of all the stars as if they were all the same distance away from Earth (10 pc (32.6 light-years)) and gives a number that indicates the actual brightness or luminosity of the star.
Compare some stars: Absolute Apparent M Sun = 4.8 m Sun = -26 M Sirius = 1.4 m Sirius = -1.46 M Betelgeuse = -5.6 m Betelgeuse = 0.50 1) Which star looks brightest from Earth? A) Sun B) Sirius C) Betelgeuse 2) Which star is brightest? A) Sun B) Sirius C) Betelgeuse
Absolute (recall at 10 pc) distance) Apparent (recall at actual I) M Sun = 4.8 m Sun = -26 II) M Sirius = 1.4 m Sirius = -1.46 III) M Betelgeuse = -5.6 m Betelgeuse = 0.50 1) Which is closest to us? Rank them from least distance to farthest. A) I = II < III B) I < II < III C) II <I <III D) III <II <I E) III <I <II
By comparing the apparent (m) and absolute magnitude (M) numbers we can estimate a stars distance from Earth. When m = M, then the star is located exactly 10 pc away When m<m, then the star appears brighter than it would if it were 10 pc away so it must be closer than 10 pc When m>m, then the star appears dimmer than it would if it were 10 pc away so it must be farther than 10 pc
By comparing the apparent (m) and absolute magnitude (M) numbers we can estimate a stars distance from Earth. OR m = M, then the distance = 10 pc m < M, then the distance < 10 pc m > M, then the distance > 10 pc