Hubble’s original diagram of distance to nearby galaxies, derived from measurements using Cepheid variables, against velocity, derived from redshift . The Hubble constant is the slope of this relation, and in this diagram is a factor of nearly 10 steeper than currently accepted values.
Illustration of the Hubble law. Galaxies at all points of the square grid are receding from the black galaxy at the centre, with velocities proportional to their distance away from it. From the point of view of the second, green, galaxy two grid points to the left, all velocities are modified by vector addition of its velocity relative to the black galaxy (red arrows). When this is done, velocities of galaxies as seen by the second galaxy are indicated by green arrows; they all appear to recede from this galaxy, again with a Hubble-law linear dependence of velocity on distance.
Positions of Cepheid variables in HST/ACS observations of the galaxy NGC 4258, reproduced from  (upper panel). Typical Cepheid lightcurves are shown in the lower panel.
Diagram of the CMB anisotropies, plotted as strength against spatial frequency, from the WMAP 3-year data . The measured points are shown together with best-fit models to the 1-year and 3-year WMAP data. Note the acoustic peaks, the largest of which corresponds to an angular scale of about half a degree.
Top: The allowed range of the parameters , , from the WMAP 3-year data, is shown as a series of points (reproduced from ). The diagonal line shows the locus corresponding to a flat Universe ( + = 1). An exactly flat Universe corresponds to H0 70 km s–1 Mpc–1, but lower values are allowed provided the Universe is slightly closed. Bottom: Analysis reproduced from  showing the allowed range of the Hubble constant, in the form of the Hubble parameter h H0 / 100 km s–1 Mpc–1, and by combination of WMAP 3-year data with acoustic oscillations. A range of H0 is still allowed by these data, although the allowed region shrinks considerably if we assume that w = –1 or = 0.
Basic geometry of a gravitational lens system, reproduced from .
The lens system JVAS B0218+357. On the right is shown the measurement of time delay of about 10 days from asynchronous variations of the two lensed images . The left panels show the HST/ACS image  on which can be seen the two images and the spiral lensing galaxy, and the radio MERLIN+VLA image  showing the two images together with an Einstein ring.
S-Z decrement observation of Abell 697 with the Ryle telescope in contours superimposed on the ROSAT grey-scale image. Reproduced from .
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