You’re probably thinking this is a short list. Space is big, sure, but how many things actually start with the letter "Y" when you move past the basics? Most people might stumble at "Yellow Dwarf" and then just sort of give up. But if you actually dig into the star catalogs and the messy history of celestial nomenclature, there's a whole lot more going on. We’re talking about massive stars that shouldn't exist, tiny brown dwarfs that are colder than a cup of coffee, and galaxies so distant they look like tiny red smudges on a telescope's sensor.
Space is weird. Honestly, the way we name things makes it even weirder.
The Most Famous Y: Yellow Dwarfs
Our Sun is a Yellow Dwarf. Technically, astronomers call it a G-type main-sequence star. It's kinda funny because the Sun isn't actually yellow; it’s white. The atmosphere just scatters the shorter wavelengths of light, like blue and violet, leaving the yellows and reds to hit your eyes. If you were floating in the vacuum of space (not recommended without a suit), the Sun would look like a blindingly white ball of fire.
Yellow dwarfs are the "Goldilocks" stars of the universe. They live for about 10 billion years, which is long enough for life to actually get its act together on nearby planets. If a star is too big, it blows up in a few million years. Too small, and it’s a temperamental Red Dwarf that shoots out flares every Tuesday.
Yellow Hypergiants: The Rare Beasts
Now, if you want something truly terrifying, look at a Yellow Hypergiant. These are not just "big" stars. They are atmospheric nightmares. There are only a handful of them known in the entire Milky Way—stars like Rho Cassiopeiae. These things are so unstable they literally throw their own outer layers into space because they’re too bright to hold onto their own gas.
Imagine a star so large that if you replaced our Sun with it, the star’s surface would swallow every planet out to Jupiter. They’re basically stars in a mid-life crisis, transitioning between being Red Supergiants and Blue Supergiants. Because this phase is so short in cosmic terms, catching one is like seeing a lightning bolt in a photo of a storm.
Yerkes: The Name Behind the Glass
If you’re into the history of how we actually see space, you’ve heard of Yerkes Observatory. Located in Williams Bay, Wisconsin, it houses the world's largest refracting telescope. We're talking about a lens that is 40 inches across.
Back in the late 1890s, George Ellery Hale convinced businessman Charles Yerkes to fund this monster. It was the "birthplace of modern astrophysics." This is where legends like Subrahmanyan Chandrasekhar worked out why stars collapse into black holes. It’s not an "object" in space, but without Yerkes, our map of the "Y" objects in the sky would be a lot emptier.
The Coldest Stars: Y Dwarfs
This is where things get really cool. Literally.
Y Dwarfs are the coldest class of brown dwarfs. Brown dwarfs are often called "failed stars" because they never got massive enough to start fusing hydrogen in their cores. They just sit there, glowing dimly from the heat of their own gravitational contraction.
For a long time, these were theoretical. Then, NASA’s WISE (Wide-field Infrared Survey Explorer) mission started finding them. Some of these Y dwarfs, like WISE 1828+2650, have temperatures lower than room temperature. You could potentially touch the surface of this "star" without burning your hand—though the gravity would crush you instantly. They represent the bridge between the smallest stars and the largest gas giant planets like Jupiter.
They don't give off visible light. To find a Y dwarf, you have to look in the infrared. They are essentially ghosts haunting the interstellar neighborhood.
Y-Type Asteroids and the Metal Mystery
Asteroids aren't just rocks. They’re classified by what they’re made of. While C-type (carbon) and S-type (stony) are common, Y-type asteroids are a bit of a niche rarity. These are actually a sub-category in some taxonomic systems, often grouped near M-types (metallic).
They have a specific "reddened" spectrum in the near-infrared. Astronomers believe these might be the remnants of the cores of shattered protoplanets. When you look at a Y-type or its cousins, you’re looking at the "bones" of a world that never got the chance to finish growing.
Names You’ve Probably Never Heard Of
Most stars are named after the constellation they are in, combined with a letter or a number. This leads to a lot of "Y" names that sound like serial numbers but represent massive, burning suns.
- Y Canum Venaticorum: Also known as La Superba. It is one of the reddest stars in the sky. It’s a carbon star, meaning its atmosphere is choked with carbon compounds that absorb blue light, making it look like a drop of blood in the constellation Canes Venatici.
- Y Cassiopeiae: A variable star that changes its brightness over time.
- Y-GZGs: These are "Young Giant-Z Galaxies." When we look at the very early universe, we see these massive galaxies forming stars at a rate that seems impossible.
The YORP Effect: How Light Moves Mountains
Okay, this isn't a physical object you can touch, but it’s one of the most important "Y" things in space. The YORP effect (Yarkovsky–O'Keefe–Radzievskii–Paddack effect) is the reason some asteroids spin so fast they literally fly apart.
It happens because of sunlight. When an asteroid absorbs sunlight, it re-emits that energy as heat. Because asteroids are usually lumpy and irregular, that heat doesn't leave the surface evenly. This creates a tiny, tiny amount of thrust. Over millions of years, this "thermal torque" can speed up an asteroid’s rotation.
The asteroid Bennu, which the OSIRIS-REx mission visited, is being affected by the YORP effect right now. It's essentially a cosmic windmill powered by light.
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Why Does Any of This Matter?
Searching for things in space that start with "Y" might feel like a trivia game, but it actually highlights the gaps in our knowledge. Y dwarfs were invisible to us for centuries. Yellow hypergiants are so rare that every new one we find changes our models of how stars die.
The universe doesn't care about our alphabet. But by categorizing these things—from the heat-powered spin of an asteroid to the freezing "surface" of a brown dwarf—we start to see the patterns.
How to Explore the "Y" Objects Yourself
You don't need a billion-dollar telescope to see some of these.
- Find La Superba (Y CVn): If you have a decent pair of binoculars and a star chart for Canes Venatici, look for a deep red star. It’s one of the most strikingly colored objects in the night sky.
- Track the Sun: Since the Sun is a Yellow Dwarf, you can study it every day. Just use a solar filter or a dedicated solar telescope. Look for sunspots, which are magnetic storms on the surface.
- Check out the WISE data: NASA’s archives are public. You can look up infrared images of Y dwarfs and see how they differ from standard stars.
- Visit Yerkes: If you’re ever near Wisconsin, go to the observatory. Seeing a 40-inch glass lens in person makes you realize how far we’ve come from just staring at the "yellow" Sun with our naked eyes.
Space is full of oddities. The "Y" category gives us a weird mix of the extremely hot, the extremely cold, and the extremely historical. Whether it's a star that's too cold to burn or an asteroid being spun like a top by sunlight, there's plenty to find if you know where to look.