Astronomy

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White dwarf
Sirius B (8.6 light-years)
Imagine a hot star the size of Earth, but with
the mass of the Sun. The transition begins
as a Sun-like star becomes a red giant, like
Aldebaran (Alpha [α] Tauri). It then ejects
its outer layers to form a planetary nebula,
and eventually settles down as a white
dwarf. Our Sun is destined to become a
white dwarf in about 5 billion years.
In the meantime, the closest white dwarf,
Sirius B (Alpha Canis Majoris B), is only
8.6 light-years away. It is the companion of
Sirius A, the brightest star in the night sky.
Originally, Sirius B was brighter and more
massive than Sirius A, but it aged faster and
evolved into a white dwarf around the time
the Cretaceous raptor Deinonychus prowled
North America. Although it is brighter than
Barnard’s Star, the glare of its luminous
companion makes it a challenge to see. It’s
currently about 10" east of the primary,

approaching the most distant part of its

50-year orbit. That means it is easier to see

now than it will be in 25 years.

Observing tip: Let Sirius drift through

your eyepiece’s field of view; the

companion lies to the east and will follow.

High magnification and a steady sky are

your friends. And light pollution won’t have

much effect on your view.

Double star

61 Cygni ( 11 .4 light-years)

Double stars orbit around a gravitational

center called the barycenter. Such systems

may have similar stars — or different, if

one has greater mass and evolves more

quickly than the other.

61 Cygni is an example of a system with

two similar stars. It’s not the closest binary

to the Sun (Alpha Centauri and Sirius are

closer) but is the nearest one north of the

celestial equator. This system’s claim to

fame is being the first to have its distance

measured with a fair degree of accuracy. In

1838, using the stellar parallax method,

Friedrich Wilhelm Bessel came up with

10.3 light-years — though today’s research

shows it to be 1.1 light-years more distant.

This is a pair of K-type dwarf stars that

complete an orbit in 659 years. Like

Sketch of 61 Cygni

Hyades cluster

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