OK, now we need to pretend we are on a planet in the Andromeda galaxy, out for a night of observing, and how often do we look at the Milky Way in our telescopes? For that estimate we can use the mirror calculation, that is, figure how often Earth's astronomers are looking at Andromeda, then draw the parallels. When we look at Andromeda, it has to be above the horizon, and it has to be the right time of year. Let's also say that an Andromedan would find that the Milky Way is an equally interesting object for amatuer viewing. A large spiral galaxy is a frequent target. For the numbers, we can use some realistic estimates. Andromeda has to be about 20 degrees above the horizon or better, and dividing the visible window by 360 degrees yields 40%. And the probability that we are in the right season is about 50% (we can always stay up very late or get up very early to see Andromeda during the "off" seasons, but let's say our prime time viewing (after work and before bed on a Saturday night) is affected by seasonal viewing windows. Next we calculate the odds that we are viewing tonight. Say its 5%, which is roughly 2 nights per month and biased because of our lunar cycle. I don't get out more than once per month, and diehards are out much more, and we don't know if our Andromedan neighbors have no moons or many moons, and they might not even sleep at night, so it's a guess. Now, on an observing night when Andromeda is in view, what are the chances we will look for it, and how long will we view it? I think it's maybe a 10% chance that we will select it for view, out of all the other interesting objects to look at, so let's assume the same for the Andromedans - when the Milky Way is up, it's one of many interesting objects, but a nice large galaxy target, so it's 1 in 10 that they look this way. Next, the probability of viewing "now" (or 3 million years ago considering the distance, take your pick). If I have a three hour viewing session, and I spend 2 minutes viewing each object that I slew to, that's roughly a 1% probability of viewing now. Assuming the same level of interest by our Andromedan neighbors, and plugging all the numbers in, we find that there are, on average, 1.08 Andromedan astronomers looking at us "while" we are peering at them. This amazing result means there is a fair chance "some one" is looking at our galaxy while you are looking at Andromeda. So the next time you are out observing Andromeda, you may be pleased to know that some one may be there looking toward you and enjoying the sight of our beautiful Milky Way galaxy.
Let's hope they have dark skies.
Mike Ricklin
Member, TAAS
Let's hope they have dark skies.
Mike Ricklin
Member, TAAS
