A raw #Keck #echelle spectrum of the #RRLyrae star currently under observation: blue is on the upper left, (infra)red on the lower right. The actual star spectrum is the thin line in all strips, the horizontal lines are sky emission lines - these are important to capture, too, because they have to be carefully subtracted from the star spectrum. Therefore the star is placed in a slit, to get the sky left and right, too.

The new #Keck target - an #RRLyrae star at the outskirts of our Galaxy in the #halo; the Virgo Cluster is too low now - has been placed behind the spectrograph slit marked with the cursor (and thus can't be seen by the guide camera now). A 45-minute exposure of a spectrum is now being taken: the goal is its #radialvelocity, for determining the #Galaxy's mass and looking for a reflex motion of the whole Milky Way caused by its Large Magellanic Cloud neighbor.

The new #Keck target - an #RRLyrae star at the outskirts of our Galaxy in the #halo; the Virgo Cluster is too low now - has been placed behind the spectrograph slit marked with the cursor (and thus can't be seen by the guide camera now). A 45-minute exposure of a spectrum is now being taken. The goal is its #radialvelocity, for determining the #Galaxy's mass and looking for a reflex motion if the Milky Way caused by the Large Magellanic Cloud.