I've been noticing for the past few days that the Moon looks huge when it rises over the horizon, much bigger than on other days. My sister says it's an optical illusion, but I was wondering if it has something to do with its orbit or if it's actually closer this time of year.
Your sister is right - it's mainly optical illusion. The Moon does orbit Earth in an elliptical orbit, so there are moments when it's closer (perigee) and farther away (apogee), but that difference in distance is pretty small - we're talking about roughly 50,000 kilometers of variation between the two points. What your eye perceives as "huge" when it rises over the horizon has almost nothing to do with that.
What you're seeing is the classic optical illusion effect: when the Moon is low on the horizon, your brain automatically compares it to nearby terrestrial objects - buildings, trees, mountains - and perceives it as much larger. Plus, when it's high in the sky, you don't have reference points, so it seems smaller. It's a trick of the brain, not orbital physics. In September 2026 there's nothing special that would make the Moon significantly closer than at other times of the year, so what you're seeing is pure perspective and visual context.
My advice: try photographing the Moon when you see it "huge" and then look at the photo on your phone. You'll be surprised how small it looks. That confirms that it's your visual perception playing tricks on you, not an actual change in size or distance.
It's not that the Moon is necessarily closer right now, but what people usually overlook is that the sensation of gigantic size when it rises over the horizon is pure optical illusion caused by terrestrial objects around it (trees, buildings, mountains) that act as a reference point and trick your brain - something that disappears when the Moon climbs higher in the sky and there's nothing nearby to compare it to anymore. If you really want to know whether it's at perigee or apogee on these specific days in September, you'd have to look up precise astronomical data, but the visual effect you're describing probably has more to do with where you're viewing it from and what's around you than with the actual distance.
The optical illusion is definitely the main thing, but there's a detail worth clearing up: the Moon's perigee and apogee do exist and do affect its actual size, it's just that the difference is pretty small, like 14% more or less, so we barely notice it with the naked eye. What we do notice a lot is when it rises over the horizon because our brain compares it with trees, buildings, and other objects, which makes it seem gigantic; up in the sky we don't have that reference and we see it smaller even though it's the same Moon. If you want to verify it, photograph the Moon with your phone when it's rising and then when it's high up, from the same spot, and you'll see that in the photo it's almost the same size in both moments.
The thing is there's nothing special about the lunar orbit in September that would explain why it looks bigger! I go out running early almost every day and I see the Moon in different phases, and I swear that whenever it comes up right on the horizon it always looks huge, regardless of the month or whether it's at perigee or apogee. It's pure optical illusion - your brain compares the Moon to buildings, trees, and earthly objects around it, and that's why it seems enormous. When you see it way up in the sky with nothing nearby to compare it to, suddenly it looks small and disappointing!
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