<p><strong>RA and DEC</strong> are the coordinates on sky.   </p>

<ul>
<li>RA (Right Ascension) is the angular position measured eastward in a full circle along the celestial equator.</li>
<li>Dec (Declination) is the angular position measured from the celestial equator in either the north (positive) or south (negative) direction. $+90\,^{\circ}$ is the north celestial pole, $-90\,^{\circ}$ is the south.</li>
</ul>

<p><strong>Velocity (km/s)</strong> is the radial velocity that the galaxy has away from or towards the earth.  </p>

<p><strong>Redshift (z)</strong> is basically a distance estimate based on observing the amount that the light of the object is redshifted due to it's movement away from us. (Since galaxies farther away will appear to move away faster according to Hubble's Law) If you understand the Doppler effect, the equation for its definition is pretty simple: (from Wikipedia's "Redshift" page)  </p>

<p><img src="https://i.sstatic.net/fr2D4.png" alt="From wikipedia on &#39;redshift&#39;"></p>

<p>The higher z is, the further away in distance (and time) the galaxy is. </p>

<p><strong>Magnitude / Filter :</strong> Magnitude is the measure of brightness of the object. This depends on which filter (at which wavelength range) the observation is made in. For this measurement: smaller values = brighter. The sun is something like -27, the brightest star Sirius, is around -1.5, the faintest stars visible to the naked eye are around +6 to +8.<br>
The galaxy page you linked only lists the magnitude - I don't know why the filter doesn't seem to be there.</p>

<p><strong>Separ. arcmin :</strong> The separation in arc minutes. (Probably meaning size, or diameter of the galaxy) An arc minute is an angular unit of size on the sphere of the sky (the same units as declination). So one arc minute is 1/60th of a degree, and there are 360 degrees spanning the entire celestial sphere.</p>

<p>Sorry, I don't know the "Qual" measurement.</p>

CC BY-SA 3.0
2014-07-24T23:01:10.200Z
2014-07-24T23:01:10.200Z
superphoton
<p>DEC :Declination</p>

<p>RA :Right ascension</p>

<p>Redshift / z  :use to calculate   velocity  over earth z axis (azimuth) </p>

<p>Magnitude/ Qual Filter : zoom into image filter quality (??)</p>

<p>Separ arc min   : if is a group as cloud magallans</p>

<p><a href="http://en.wikipedia.org/wiki/Equatorial_coordinate_system" rel="nofollow">here more information</a></p>

CC BY-SA 3.0
2014-07-22T20:28:03.710Z
2014-07-22T20:28:03.710Z
Adrian R
<p>complete beginner here, only got into star gazing a few days ago using my friend's telescope and I don't really understand at all what any of the measurements mean.</p>

<p>Anyway, talk about jumping in the deep end, but I'm poking around Nasa's Intergalactic Database, but sadly it's all greek to me: <a href="http://ned.ipac.caltech.edu/" rel="nofollow">http://ned.ipac.caltech.edu/</a></p>

<p>Here's a galaxy: <a href="http://ned.ipac.caltech.edu/cgi-bin/objsearch?objname=NGC+7590&amp;extend=no&amp;hconst=73&amp;omegam=0.27&amp;omegav=0.73&amp;corr_z=1&amp;out_csys=Equatorial&amp;out_equinox=J2000.0&amp;obj_sort=RA+or+Longitude&amp;of=pre_text&amp;zv_breaker=30000.0&amp;list_limit=5&amp;img_stamp=YES" rel="nofollow">NGC 7590</a></p>

<p>Here's its basic data:</p>

<p><strong>EquJ2000.0 RA</strong></p>

<p><strong>EquJ2000.0 DEC</strong></p>

<p><strong>Velocity km/s</strong></p>

<p><strong>Redshift / z</strong></p>

<p><strong>Magnitude / Qual Filter</strong></p>

<p><strong>Separ arc min</strong></p>

<p>Now I'm afraid I don't really understand what any of these measurements and their values actually mean.</p>

<p>I remember from school what Red Shift is, its the wavelength increasing becoming 
'stretched' making the light seem to appear more reddish the faster an object is accelerating away from us. But what is that z unit?</p>

<p>I'm afraid I really don't have a clue regarding anything else... spear arc min, magnitude / qual filter?</p>

<p>Is there a book for a brief understanding of these units? Not out to solve problems regarding celestial mechanics, I just want the NED to make a bit more sense to me so I can visualize these objects.</p>

<fundamental-astronomy><redshift><units>
Basic celestial data
Starkers
# Basic celestial data

(Asked by: username_0 on 2014-07-19)

complete beginner here, only got into star gazing a few days ago using my friend's telescope and I don't really understand at all what any of the measurements mean.

Anyway, talk about jumping in the deep end, but I'm poking around Nasa's Intergalactic Database, but sadly it's all greek to me: <http://ned.ipac.caltech.edu/>

Here's a galaxy: [NGC 7590](http://ned.ipac.caltech.edu/cgi-bin/objsearch?objname=NGC+7590&extend=no&hconst=73&omegam=0.27&omegav=0.73&corr_z=1&out_csys=Equatorial&out_equinox=J2000.0&obj_sort=RA+or+Longitude&of=pre_text&zv_breaker=30000.0&list_limit=5&img_stamp=YES)

Here's its basic data:

**EquJ2000.0 RA**

**EquJ2000.0 DEC**

**Velocity km/s**

**Redshift / z**

**Magnitude / Qual Filter**

**Separ arc min**

Now I'm afraid I don't really understand what any of these measurements and their values actually mean.

I remember from school what Red Shift is, its the wavelength increasing becoming
'stretched' making the light seem to appear more reddish the faster an object is accelerating away from us. But what is that z unit?

I'm afraid I really don't have a clue regarding anything else... spear arc min, magnitude / qual filter?

Is there a book for a brief understanding of these units? Not out to solve problems regarding celestial mechanics, I just want the NED to make a bit more sense to me so I can visualize these objects.

**Tags:** fundamental-astronomy, redshift, units

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## 2 answers

### Answer by username_1 on 2014-07-24. Score: 2

**RA and DEC** are the coordinates on sky.

* RA (Right Ascension) is the angular position measured eastward in a full circle along the celestial equator.
* Dec (Declination) is the angular position measured from the celestial equator in either the north (positive) or south (negative) direction. $+90\,^{\circ}$ is the north celestial pole, $-90\,^{\circ}$ is the south.

**Velocity (km/s)** is the radial velocity that the galaxy has away from or towards the earth.

**Redshift (z)** is basically a distance estimate based on observing the amount that the light of the object is redshifted due to it's movement away from us. (Since galaxies farther away will appear to move away faster according to Hubble's Law) If you understand the Doppler effect, the equation for its definition is pretty simple: (from Wikipedia's "Redshift" page)

![From wikipedia on 'redshift'](https://i.sstatic.net/fr2D4.png)

The higher z is, the further away in distance (and time) the galaxy is.

**Magnitude / Filter :** Magnitude is the measure of brightness of the object. This depends on which filter (at which wavelength range) the observation is made in. For this measurement: smaller values = brighter. The sun is something like -27, the brightest star Sirius, is around -1.5, the faintest stars visible to the naked eye are around +6 to +8.  
The galaxy page you linked only lists the magnitude - I don't know why the filter doesn't seem to be there.

**Separ. arcmin :** The separation in arc minutes. (Probably meaning size, or diameter of the galaxy) An arc minute is an angular unit of size on the sphere of the sky (the same units as declination). So one arc minute is 1/60th of a degree, and there are 360 degrees spanning the entire celestial sphere.

Sorry, I don't know the "Qual" measurement.


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### Answer by username_2 on 2014-07-22. Score: 1

DEC :Declination

RA :Right ascension

Redshift / z :use to calculate velocity over earth z axis (azimuth)

Magnitude/ Qual Filter : zoom into image filter quality (??)

Separ arc min : if is a group as cloud magallans

[here more information](http://en.wikipedia.org/wiki/Equatorial_coordinate_system)


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