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Arcturus
Details
Arcturus is a bright orange giant and the brightest star in the northern celestial hemisphere. It also races unusually fast across the sky for such a bright star, shifting by about two arcseconds per year because of its high motion relative to the Sun.
Arcturus is the brightest star in the northern celestial hemisphere, but brightness is not the only thing that makes it memorable. It is an orange giant, a star that has already moved beyond its quieter main-sequence years. That gives it a soft, warm color and a sense of maturity that fits its presence in the sky.
What makes Arcturus especially interesting is that it is not fixed in the heavens as much as it seems. It moves unusually quickly relative to the Sun, drifting across the sky with a high proper motion that marks it as a star in motion even on very long timescales. Arcturus is therefore not just a beacon but a traveler.
That combination matters because it makes Arcturus feel alive in two different senses. It is bright enough to stand out immediately, yet it also carries the subtle evidence of change and motion. Arcturus is one of those stars that reminds us the sky is not a painted ceiling but a moving system.
13.0million km
Visual creditscaleofspace.org / CC BY-NC 4.0
Key facts
- Category
- Stars
- Object class
- K-type giant star
- Mass
- ~1.1 solar masses
- Temperature
- ~4,300 K surface
- Scale fact
- 35 million kmdiameter
- Estimated age
- ~7.1 billion years
- Composition
- Hydrogen and helium
Scale context
Where Arcturus sits on the full axis
By size on the journey, Arcturus sits between Sagittarius A* and Aldebaran. The band below uses nearby Stars objects for context.
Shared physical scale
67.0million km
Together, these objects make the size change around Arcturus easy to compare at a glance.
Between the smallest and the largest, perspective is everything.
About
Scale of Space is a scroll-based journey through the universe, placing objects on a single logarithmic scale so you can compare size across an unbroken range.
Guides turn parts of that scale into curated essays, while focused views let you explore the same range through specific groups of objects.