Alphard is Hydra’s brightest star at mag. +2.0, and it sits in an otherwise rather barren part of the sky.
Appropriately, the name ‘Alphard’ means ‘solitary one’.
Covering an area of 1,303 deg2, Hydra the Water Snake is the largest constellation of all, but also a little obscure.
Most of its pattern, representing the body of the snake, is marked by relatively faint stars.
The head of the snake is more distinctive – a sideways tear-drop pattern south of Cancer, the Crab.
The snake’s ‘neck’ falls southeast of the head and it’s here you’ll find orange giant star Alphard (Alpha (α) Hydrae).
Alphard’s visibility in the northern hemisphere in the night sky in the early part of the year denotes the oncoming of spring, and the star is visible throughout springtime.
Facts about Alphard
Physically, Alphard is around 50 times larger than our Sun but contains only three times the mass.
Its spectrum is K3II–III, the K3 meaning it is in the orange part of the stellar classification system that ranks stars according to temperature.
The II–III indicates it’s a class of star between a bright giant and a normal giant.
Having exhausted much of its hydrogen, Alphard is now fusing helium into heavier elements such as oxygen and carbon in its core.
The star exhibits regular oscillations ranging from hours to days. It also has a small excess of barium.
This is usually seen in binary systems where matter has been transferred from a white dwarf.
No such companion is visible close to Alphard.
Two more distant companions can be seen, of which only one, Alphard B, 282 arcseconds away, is considered to be a candidate for a true gravitational companion.
Have you observed or photographed Alphard? Share your observations and images with us by emailing contactus@skyatnightmagazine.com
This guide appeared in the February 2019 issue of BBC Sky at Night Magazine.