Sky & Telescope - January 2025 - 45

Stories in the Stars by Stephen James O'Meara
A Parade of Colors
Several pairings of planets and stars offer a
chance to test your color perception.
J
anuary's night sky contains three
playful pairings that include some
of the most brilliant stars and planets
in the heavens. They're strung out
across the sky like colorful gems adorning
the necklace of the ecliptic - the teal
line that indicates the path of the Moon
and planets across the sky on our allsky
charts (pages 42-43 and page 44).
As the month progresses, Venus joins
Saturn low in the west while Jupiter
keeps watch over Aldebaran, in Taurus,
high overhead. And in the eastern sky,
Mars dances with the celestial Twins,
Castor and Pollux, in Gemini. More
than just interesting interplay, these
pairings provide opportunities to seek
out delicate hues.
A star's color is a direct indicator
of its surface temperature. The hottest
stars we can see with our unaided eyes
are blue-white, while the coolest ones
are reddish; those with temperatures
similar to our Sun's appear yellowish.
The stars we're focusing on this month
have an array of hues: Aldebaran is an
orange giant; Betelgeuse, in Orion, is
a red giant; and Capella, in Auriga, is
a yellow, Sun-like star. Castor appears
blue-white, while Pollux is another
orange giant.
Planets, on the other hand, shine
by reflected sunlight, so their colors
mainly depend on the specific planet's
characteristics and on the effects of
Earth's atmosphere. For instance, when
Venus is highest it shines brilliantly
white, but when it's near the horizon -
as it is this month - its color appears
warmer due to the same atmospheric
effect that gives us red sunsets. Saturn
usually looks golden-hued, but it too
is low in the sky, where it may appear
more orange. Jupiter is much higher
and under ideal atmospheric conditions
displays an untainted creamy luster. But
don't be fooled
by Mars's nickname
- the Red
Planet usually
isn't red. Instead,
it appears more
golden than
red when it
glows brightly
around the time
of opposition,
which occurs
this month on
the 16th.
No matter a star or planet's true
color, how it looks to each of us is never
clear-cut. Everyone has slightly different
color perception, so what each of
us sees is subjective at best. And there's
also a phenomenon called simultaneous
contrast, which affects how we perceive
two adjacent colors - each influencing
how the other looks. This includes stars
and planets seen against the background
sky, which can be velvety black, twilight
blue, dusty red, or tinted orange by the
glow of sodium-vapor lamps. Have a
look at Jupiter in twilight when the sky
is still deep blue - will it have the same
color later at night?
Returning to this month's celestial
pairings, let's first nab Venus and Saturn
before they set. As noted on page
46, the best date to catch them is January
3rd, when a waxing crescent Moon
lies between them. All three objects
will be very low in the southwest and
subject to atmospheric reddening. With
each passing night in January, Venus
and Saturn inch closer to each other.
Does their proximity have an effect on
the hues you see?
Jupiter, on the other hand, reigns
supreme high overhead near Aldebaran,
offering a wonderful opportunity
to contrast their colors. Does Jupiter's
This photo of the conjunction between
Jupiter and Mars captures the naked-eye view
on the morning of August 14, 2024. At the time,
the planets were just 19′ apart.
presence near Aldebaran affect what
you see? Block the star with your hand.
Does Jupiter's color change when the
star is absent? In August 2024, Mars,
Aldebaran, and Betelgeuse were roughly
the same brightness and appeared
to share the same orange hue. It was
a captivating sight, as shown in the
photo above. Since then, the scene has
changed. Mars has moved on, and even
Betelgeuse might look a little different.
It's a variable star whose brightness
typically fluctuates by only a couple of
tenths of a magnitude, though in 2019
it dimmed dramatically by more than a
full magnitude (S&T: Mar. 2021, p. 14)!
As January progresses, Mars is zeroing
in on pale-orange Pollux. Be sure
to compare both Mars and Pollux to
blue-white Castor and with yellow Procyon,
in Canis Minor. Mars outshines
all three stars, but will its proximity to
Pollux enhance or diminish its redness?
You be the judge.
¢ Contributing Editor STEPHEN JAMES
O'MEARA has been studying the stars
and their lore for more than 50 years.
sk yand tele scope .o r g * JANUARY 2025 45
BOB KING
http://skyandtelescope.org
Sky & Telescope - January 2025

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