Delta (δ) Aurigae is the main star at the top of Auriga, the constellation that looks like a misshapen pentagon.
Delta on top of the pentagon forms a triangle along with Capella (Alpha (α) Aurigae) and Menkalinan (Beta (β) Aurigae) as the triangle’s base.
It shines at mag. +3.7 and so is an easy naked-eye star, but despite its labelled position as Delta, it’s outshone by Epsilon (ε), Eta (η), Theta (θ) and Iota (ι) Aurigae.
Facts about Delta Aurigae
Delta’s spectral class is K0 IIIb, K0 indicating an orange star and the IIIb indicating that it’s a less luminous evolved giant star.
It’s slightly younger than our Sun at 3.26 billion years and is believed to be a red clump star, one that fuses helium in its core.
It’s also known to be a spectroscopic binary with an orbital period of 3.52 years. The main star is 1.63 times more massive than our Sun and approximately 11 times larger.
It spins on its axis at the leisurely rate of 4km/s, twice the rotation speed of the Sun. The system is 141 lightyears distant.
Finding the North Star
Delta has a special place in the sky, forming an asterism with Menkalinan and Theta Aurigae that on a map appears like a perfectly straight line.
Nothing special here you might think, until you realise that extending this line northwards points with an impressive degree of precision directly at Polaris, the North Star.
Even the traditional ‘pointer’ stars, Dubhe (Alpha (α) Ursae Majoris) and Merak (Beta (β) Ursae Majoris), don’t point as precisely as the Theta–Beta–Delta Aurigae line!
Do you have a better way to find the North Star? Let us know by emailing contactus@skyatnightmagazine.com
This guide appeared in the February 2025 issue of BBC Sky at Night Magazine
