Star Trek

All motion is relative.  For example, you may be reading this is in a stationary chair but you are moving!  If you live in Milwaukee, you are actually moving over 700 mph (.3 km/s) eastward due to the rotation of the Earth.  And then again, the Earth is moving around the sun at about 67,000 mph (30 km/s).   But the story doesn't end there and that is the topic of this question.  Each answer is worth 3 points unless where indicated.  Please report all speeds in km/s.

Our sun is also in motion but you have to be careful to define what that motion is relative to.

  1. Astronomers have defined a reference point related to the sun's motion in space abbreviated the LSR.  What is that? (4 points)

    The LSR is known as the Local Standard of Rest.  Imagine a point which is exactly the same distance from the center of the galaxy as the sun but moving around the galactic center in a perfect circle at a constant speed.  This would be a perfect reference point to make galactic motion measurements.  As it turns out, if you take all the stars located around the solar neighborhood and calculate their AVERAGE motion, it comes pretty close to the LSR.  For our purposes, we can treat them the same.  You may be confused why astronomers might need this strange reference point so let me explain.  Imagine a swarm of bees flying as a group.  One speed measurement could describe the motion of the swarm itself and another could describe the motion of one individual bee within the swarm (which would be random from one bee to another).  This is exactly the problem astronomers had with describing how stars move around a galaxy.  Now imagine the LSR is the motion of the swarm of stars around our sun and the sun itself is a single bee within that swarm (with its own random motion with respect to the swarm).  Get it?
     
  2. How is our sun moving with respect to the LSR?

    According to this source:

    The Sun is moving


     

  3. How fast is the LSR moving with respect to the galactic center?

    Essentially the sun is zooming around the Milky Way at a whopping 230 km/s.  As you read in the eBook, it will take 225 million years to make one galactic round trip.
     
  4. Within our local group of galaxies, how are we moving with respect to the Andromeda galaxy?

    We are heading toward the Andromeda Galaxy at a speed of 130 km/s but don't worry, the collision won't happen for another 5 billion years (about the time our sun dies).
     
  5. There is something out there called "The Great Attractor".   If the Milky Way were a piece of gravel, the Great Attractor would be a truck 150 million ly away.  What is our motion with respect to this mysterious object?

    Whatever this thing is, we are moving toward it at about 600 km/s (but numbers vary from one source to another).

    After this, the expansion of the universe takes over and everything is red shifted according Hubble's Law (as described in the eBook).
     
  6. On the grandest scale, how are we moving with respect to the Big Bang? (4 points)

    When we study the cosmic background radiation (the (remnant of the Big Bang), it turns out we are overall Doppler red shifted when looking at one direction of the sky and Doppler blue shifted in the opposite direction.  That means we are moving with respect to the Big Bang.  There are actually two ways you can answer this.  If you just reference the sun, our speed is about 368 km/s with respect to the cosmic background radiation.    However, you will read in unit 5 that there is another reference point known as the Local Group.  This is the bunch of gravitationally connected nearby galaxies and the Milky Way is a member of it.   As it turns out, the Milky Way is moving with reference to the Local Group ..... so .... we (the Local Group) are moving at 630 km/s with respect to the Big Bang in the direction of Leo and Virgo.