This smudge is a star cluster located by one of the “feet” of the two brothers constellation, Gemini. It’s two bright stars, Castor and Pollux, along with bright Jupiter, make it an easy constellation to find now. M35 is located on the outside foot of the brother Castor. Cool fact, Castor is a 6 star system. It’s slightly dimmer brother is confirmed to have a planet that takes it 590 Earth days to circle the star. Once you locate Castor, move down the body, past Jupiter, and find the outer foot. It will be 3 slightly curved stars. M35 is right above, and to the outside, of the last star (in the foot).
Unlike other clusters I’ve posted (like M45 – Pleiades/Seven Sisters) it is not an obvious naked eye object. It is sometimes, though only under very optimal conditions. However, it is an open cluster (like M45, M41 and Beehive Cluster) and very large. Pleiades is just a few hundred light years away, this one is about 2,500 light years away. Despite it’s distance, it still takes up the same size in the sky as the full Moon does.
That’s what makes it tricky to see. In wide photos it is simple – it’s the noticeable smudge near Castor’s foot. However, even though it’s bright enough overall, the fact it takes up so much space means it’s brightness is spread over a wide area. The higher you zoom, the dimmer it appears.
If we were as close to it as we are to Pleiades, it wouldn’t even appear as a cluster. Hyades, the cluster representing Taurus the Bull’s head/horns is so close most don’t recognize it as a cluster. The Big Dipper, largely, is made up of stars in what’s known as the Ursa Major Cluster/Ursa Major Moving Group. The Ursa cluster is spiraling apart, but even if it wasn’t, it wouldn’t appear as a cluster. It’s too close.