Complete this activity by 9am on Wednesday morning
Please start it before you begin your travel to Green Bank and bring
questions for discussion with others en route to GB

Scavenger Hunt #0 for 2017

Useful links:
  • Using Arecibo for ALFALFA       A2010 observer's page

    • Note: Scavenger hunts aren't exams covering the material in the last three chapters, and they are not for the faint of heart. Don't expect the answers to be trivial and/or "google-able".
    If possible, try to install and explore TOPCAT before you come to GB. Or, if you haven't had a chance to figure TOPCAT out, sit with someone else who has used it on the bus.

    0.0   Introduction to TOPCAT   (If you have not used it before..)
    If you have not used TOPCAT before, consult these notes and try out the exercise it contains. You will also find useful information on the UAT Google docs page. (Ask if you don't know about that!). Since many members of the UAT are familiar with using TOPCAT, this workshop is a great opportunity for you to learn how to use it!

    0.1   Getting oriented to the local sky
    Below is a schematic diagram of the local sky as observed from Green Bank
    Fact: The Green Bank Telescope is located at 79.8398° W longitude, 38.4322° N latitude.
    Fact: On June 14, 2016, the Sun's declination will be +23° 20'.
    Imaging that you are standing at the center looking up. Label on this diagram the following:
    • horizon
    • zenith
    • meridian
    • cardinal directions N,S,E,W
    • North Celestial Pole
    • Celestial Equator
    • Sun's path on June 14, 2017

    0.1   The sky view from Arecibo
    Below is a schematic diagram just like the one above. In this case, label the same points but as they would be seen from Arecibo.
    Fact: The Arecibo Telescope is located at 66.7528° W longitude, 18.3464° N latitude.
    Imaging that you are standing at the center looking up. Label on this diagram the following:
    • horizon
    • zenith
    • meridian
    • cardinal directions N,S,E,W
    • North Celestial Pole
    • Celestial Equator
    • Sun's path on June 14, 2017

    0.3   Observing galaxies at radio wavelengths

    To help you understand our technical radio astronomy jargon, use any on-line resources or textbooks to find the answers to these questions:

    Fact: The rest wavelength of the 21 cm HI line is 1420.4058 MHz.

        a.   What is the "L-band" in radio astronomy?

        b.   Why is the unit of flux density called a Jansky?

        c.   What range of frequency does the "radio spectrum" cover?

        d.   What range of wavelength does the "radio spectrum" cover?

        e.   In what energy state is the hydrogen atom when the 21 cm line is emitted?

        f.   The HI 21 cm line transition is highly forbidden; why then do we see it so easily?

    In extragalactic astronomy, we normally use "z" to indicate the observed redshift (or blue shift). Because distant galaxies are moving away from us at velocities that are a significant fraction of the speed of light, we need to adopt the relativistic doppler formula to relate z to a recessional velocity. This relation defaults to the simple doppler formula for v << c. See the equations to the right.

        g.   At what frequency would be observe the HI in a galaxy at a distance of 70 Mpc from us?   Hint: What is "Hubble's Law"?

        h.   Over what frequency range would be expect to see HI line emission from the Milky Way?


    0.4   Beams, drifts and the resolution of the Arecibo telescope

        a.   The diffraction limit of a telescope can be described by the cartoon to the right. What is the diffraction limit of a 305 meter diameter telescope at 21 cm?

        b.   What is the beamwidth of the Arecibo L-band wide receiver system?

        c.   Why aren't your answers to a. and b. the same?

        d.   ALFALFA was undertaken in a drift-scan mode whereby the azimuth arm is held fixed (usually parked on the meridian) so that the sky drifts by as the Earth rotates. For a beamwidth of 3.5 arcmin (approximately that of one of the ALFA feed horns), how long does it take for a source to drift across one beam?


    0.5   Using Public Databases to Explore our Targets

    We use lots of public databases to explore the universe. To get you started, investigate three of them to understand what kinds of data they contain and how to use them.
  • Sloan Digital Sky Survey
  • Digitized Sky Survey at STScI
  • NASA Extragalactic Database (NED)


    Fact: The HI 21 cm line from the galaxy known to us as UGC 987 was detected by the ALFALFA survey at a heliocentric recessional velocity of ~4650 km/s. Use the links below to investigate information about UGC 987 in the public galaxy databases.
    UGC 987   012531.5+320809   21.3812 32.1358     DR9Navi   DR12Navi   DSS2blu.03     NED1.0

        a.   What does "UGC" stand for? What catalogs do some of this galaxy's other names refer to?

        b.   Experiment with the differences in display tools for DR9 and DR12 of the SDSS image for this galaxy. What does "DR" mean?

        c.   How many HI line spectra (of UGC 987) obtained using the Arecibo telescope are available in the NED database?


    Fact: The HI 21 cm line from the galaxy known to us as AGC 102274 was detected by the ALFALFA survey at a heliocentric recessional velocity of ~4700 km/s. Use the links below to investigate information about AGC 102274 in the public galaxy databases.
    AGC 102274   004720.4+260147   11.8350 26.0297     DR9Navi   DR12Navi   DSS2blu.03     NED1.0

        d.   Estimate the inclination of this galaxy where an inclination of 0° indicates the galaxy's disk is in the plane of the sky and 90° means its disk is edge-on.

        e.   Where does the redshift given in NED come from?

        f.   NED lists many different distances for this object. What do the different distances refer to?


    Fact: During the ALFALFA team observations undertaken using the L-band wide receiver at Arecibo in November 2013, the HI 21 cm line from the galaxy known to us as AGC 103425 was detected at a heliocentric recessional velocity of ~800 km/s. Use the links below to investigate information about AGC 103425 in the public galaxy databases.
    AGC 103425   004129.4+220231   10.3725 22.0419     DR9Navi   DR12Navi   DSS2blu.03     NED1.0

        g.   What is the distance to this object? How certain is this distance?

        h.   How large (linear diameter) is the galaxy? How does its size compare to that of the Milky Way? Be sure you keep track of how you obtained the answer.

        i.   Is the galaxy forming stars at the current epoch? How do you reach your conclusion?


    Fact: During the ALFALFA team observations undertaken using the L-band wide receiver at Arecibo in November 2015, the HI 21 cm line from the galaxy known to us as AGC 125245 was detected at a heliocentric recessional velocity of ~4300 km/s. Use the links below to investigate information about AGC 125425 in public galaxy databases.

    AGC 125425   025139.7+334648   42.9154 33.7800     DR9Navi   DR12Navi   DSS2blu.03     NED1.0

        j.   Compare this galaxy to the previous two.


    Be sure you know what databases these links take you to. They will be very useful later.


    0.6   Communicating with ET
    Let us suppose that there are some extraterrestrial beings in the vicinity of the Solar System whose lifeform resembles that of a many pointed star and that they intercept a junk U.S. spacecraft containing a partly degraded plaque showing the illustration to the right.

    Where does this illustration come from and what is its intended meaning?
    Click here for larger view.


    0.7   ALFALFA Team Trivia: Part I (i.e., really important stuff)

        a.   Why does the ALFALFA team always begin enumerated lists with "0" (not "1")?

        b.   In the 2000 movie about the live tv coverage of the Apollo 11 Moon landing, what theme does the local Australian band play as the U.S. national anthem?

        c.   What radio astronomy pioneer discovered, through experiments conducted in Green Bank, that climbing bean plants produce more massive beans if they climb opposite to their natural twining direction?


    0.8   Learning PYTHON   (OPTIONAL but recommended!)
    Although we won't be using it much in this workshop, we suggest that you learn python. Here are some handy notes to get you started. Bring your questions with you to Green Bank.


    This page created by and for the members of the awesome ALFALFA Survey Undergraduate team

    Last modified: Thu Jun 8 15:01:44 EDT 2017 by martha