Universe Puzzle No. 7

As with last week’s Universe Puzzle, something that cannot be answered by five minutes spent googling, a puzzle that requires you to cudgel your brains a bit, and do some lateral thinking. This is a puzzle on a “Universal” topic – astronomy and astronomers; space, satellites, missions, and astronauts; planets, moons, telescopes, and so on.

As this week’s puzzle may be a bit harder than most, I’ll be adding a HINT tomorrow, if it looks like no one is even close to being on the right track.

UPDATE: Answer has been posted below.

What do the following objects have in common?
NGC 6822, NGC 598, NGC 221, NGC 224, and NGC 5457.

Together with the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC), these are the seven galaxies (“nebulae”) with the most reliable distances, used by Edwin Hubble to establish the distance-redshift relationship, in his landmark 1929 paper. Today we call this the Hubble relationship.

“The data are given in table 1. The first seven distances are the most reliable, depending, except for M 32 the companion of M 31, upon extensive investigations of many stars involved.”

Hubble, Edwin, “A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae” (1929) Proceedings of the National Academy of Sciences of the United States of America, Volume 15, Issue 3, pp. 168-173

Note that not all are in the Local Group, and they are not the five brightest galaxies in Table 1. Figure 1 from that paper is reproduced in the Universe Puzzle graphic; it’s at the top right.

Well done Matthew Burns and iantresman!

Check back next week for another Universe Puzzle!