This is from the NED

What do these three titles mean?

  • log fb (Jy)
  • MRK 1014
  • Log v (HZ)

Why is there LINE,LINE,LINE,LINE,LINE written along the bottom? What does that signify?

What are the dots and lines showing? A range of information? In that chase, what's the relevance of the dot?

Is it like this: The dot is the log v and then the horizontal line shows the range of MRK 1014 recorded for that log v and the vertical line showing the log fv recorded for it?

Why does the log v between 12 - 16.3 have small amounts of log fv and MRK 1014, but the log v between 15 - 19 have no log fv at all, but a large amount of MRK 1014. The same goes for the 2 log v points between 10.4 - 12, except these two have a large amount of log fv but no MRK 1014

Maybe if you could explain the units to me and give me links to further reading it would all become a lot clearer...

Update Okay MRK 1014 is the same of the object. (Doh!) However, what is that titless axis showing?

  • 1
    $\begingroup$ NED is a terrible place to start learning astronomy. It's meant as a data source and reference for the astronomical community. I would start with an introductory astronomy text book or an introductory astronomy course online. $\endgroup$
    – Aaron
    Jul 22, 2014 at 23:22
  • $\begingroup$ @Aaron I fear you're right. Can you recommend a book / online source? I want to go from no knowledge to understanding the NED's data. No crazy stuff just yet, just what all the units mean. $\endgroup$
    – Starkers
    Jul 22, 2014 at 23:35
  • $\begingroup$ I would start with something like this: en.wikibooks.org/wiki/General_Astronomy. Also: en.wikipedia.org/wiki/List_of_common_astronomy_symbols and use the links to learn more about what each symbol means. $\endgroup$
    – Aaron
    Jul 22, 2014 at 23:41

1 Answer 1


This is a spectral energy distribution (SED). Since astronomical objects don't emit light a single frequency an SED tells you how much emission you're getting across a range of frequencies.

  • "log" indicates it's on a logarithmic scale
  • $\nu$ represents frequency in Hz (e.g. $log~\nu=12$ is $10^{12}$ Hz)
  • Jy is a unit of specific flux density $f_{\nu}$ is the specific flux
  • MRK 1014 is the name of the object
  • Each of the points are observations there is a link on the page for "photometric data points" to see where everything comes from. All the positions have a point, which is measurement of the specific flux density at that given frequency. The vertical lines are the error bar for the flux measurement and the horizontal is the range of frequencies a measurement covers (e.g. a filter might have a central frequency but it filters light over a range of frequencies).
  • There are a few upper limits which are indicated by vertical lines with arrows pointing down.
  • LINE indicates that this is an estimate from a spectrum and it is the measurement of the flux of that line, not from a imaging filter.

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