Arcturus size and scale context

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. Read its scale context, comparisons, and journey links on the canonical object page.

PolluxK-type orange giant star·12.5 million km

Sagittarius A*Supermassive black hole·24.5 million km

ArcturusK-type orange giant star·35 million km

AldebaranK-type red giant star·62.8 million km

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Black holes

Sagittarius A*

Sagittarius A* is the supermassive black hole at the center of the Milky Way. Event Horizon Telescope observations imaged the glowing material around it, resolving a radio source about 52 million kilometers across around a black hole of roughly 4.3 million solar masses.

Scale fact24.5 million kmevent horizon diameter

Object class: Supermassive black hole
Host: Milky Way
Mass: ~4.3 million solar masses

Stars

Arcturus

Scale fact35 million kmdiameter

Object class: K-type orange giant star
Mass: ~1.1 solar masses
Temperature: ~4,300 K surface
Estimated age: ~7.1 billion years
Composition: Hydrogen and helium

Stars

Aldebaran

Aldebaran is a red giant branch star in Taurus with a cool orange surface and a diameter about 45 times the Sun’s. It lies in front of the Hyades cluster by chance, so it appears to sit among the bull’s-head stars without actually belonging to that group.

Scale fact62.8 million kmdiameter

Object class: K-type red giant star
Mass: ~1.03 solar masses
Host: Aldebaran system
Estimated age: ~6.4 billion years
Composition: Hydrogen and helium
Temperature: ~3,900 K surface