Quasar 3C 273



Subject: Quasar 3C 273 in Virgo.
Telescope: Takahashi FSQ-106n f/5.
Mount: Losmandy G-11
Imager: SBIG ST-7 non-E non-ABG -15 degrees C
Image Details: A single 5 minute integration of this remote object. This serves as a finder chart for those interested in finding this odd little subject. Red-shift measurements place this object some 2+ billion light-years away from Earth: the most distant object yet recorded on CCD by us here at the Northwood Ridge Observatory. 28 April 2001. Magnitude estimate done using false aperture photometry in MaxImDL. 3C 273 is located at (Year 2000 epoch):
RA: 12:29:06.698
Dec: +02:03:08.58

Determining Redshift:

The redshift of a distant object is measured by comparing the absorption lines or emission lines of that object against a known reference. I chose to use the star Theta Leonis (spectral type A3v) as a reference due to its easily recognizable Hydrogen lines. Quasars are known to have strong emission lines of Hydrogen (both Alpha and Beta in the Balmer Series).

The spectra of both objects were obtained the same evening using identical circumstances: temperature of the CCD was steady at -20C, the telescope was a Celestron 8 (200mm) operating at f/6.3. The focus was not altered between images.

Spectrum of the star Theta Leonis (used as a calibration) and the quasar 3C 273. Note the bright emission Hydrogen lines in 3C 273’s spectrum:



Once obtained, the spectrum of Theta Leonis was calibrated using VSpec software using the Hydrogen Beta line at 4861.33 Angstroms and the 0-order image of the star for reference. Once calibrated, the number of pixels per Angstrom is known (17.49756 A/p). By measuring the position of the quasar’s 0-order image from its Hydrogen Beta emission line in pixels, we can determine how many Angstroms the line has been shifted towards the red end of the spectrum.


In this case, 3C 273 has had its Hydrogen Beta line, Hb, (normally at 4861.33 Angstroms) shifted to 5640.34 Angstroms. Using the formula:


or: z = (quasar wavelength – local star wavelength) / wavelength at rest

we arrive at a value of z = 0.1602, which is as expected. This corresponds well with the accepted results of z = 0.158339

Now, considering that the quasar is moving at relativistic speeds, a slight modification of the formula should be taken into account, so we use the following:


Plugging our value for z into the above equation yields a value of z = 0.1475, which is still close to the expected 0.158339 that is published by professionals. For more details, please see the NASA Extragalactic Database

The distance to 3C 273 depends upon the value of Hubble’s Constant (H). If H is assumed to be 75km/s/Mpc, then 3C 273 resides some 2 billion light-years away. If H is assumed to be 60, then 3C 273 resides some 2.6 billion light-years away. At such a distance, objects have their light dimmed by 38.9 magnitudes! In order for us to even see 3C 273 means that it must be incredibly bright. Latest estimates point to 3C 273 being as bright as 2 trillion (1012) of our suns! That would make it as bright as 100 times the combined light of all the stars in our Milky Way Galaxy.