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Meet Dubhe, Giant of the Big Dipper – Sky & Telescope

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Dubhe Vitals

Official identify Dubhe
Different designations Alpha Ursae Majoris (α Uma), HR 4301, HIP 54061
Obvious magnitude 1.79
Distance 123 light-years
Kind Orange big, K0 III
Colour Orange
Mass four.25 M
Radius 30 R
Constellation Ursa Main
Proper Ascension 11h 03m 44s
Declination +61° 45′ 04”
A number of system? Sure, spectroscopic binary, plus two further stellar companions
Variable star? Suspected
Exoplanet standing none
Possible destiny white dwarf


Big Dipper, stars labeled
The Large Dipper, with stars labeled.
Daniel Johnson

Virtually everybody
acknowledges the Large Dipper, and also you’ve in all probability seen it numerous occasions
your self. However tonight, exit and take a more in-depth look, paying particular consideration
to the colour of the celebs. Chances are you’ll discover one thing that you simply haven’t earlier than: the
stars are all whitish-blue apart from one: The lone standout is orange Dubhe.

Though Dubhe is
the Alpha star of Ursa Main, it’s truly barely dimmer than Alioth, the
Epsilon star. Dubhe’s heat coloration stems from the truth that it’s an getting older big.
Dubhe has used up the hydrogen in its core and has resorted to fusing helium
as a substitute, increasing into a large 30 occasions the Solar’s width. It cooled because it grew,
and its present temperature offers the star its orange coloration.

Dubhe differs from different Large Dipper stars in one other means. Many of the others are members of the Ursa Main Transferring Group, which is strictly what it appears like: This cohesive group of stars with an identical historical past strikes in the identical normal course, although the celebs themselves are extra extensively separated than, say, a star cluster like the Pleiades. However Dubhe isn’t a member of the Ursa Main Transferring Group, so it — together with Alkaid, the star on the finish of the Dipper’s tail — travels by means of house individually.

However Dubhe isn’t alone.
First, it’s a spectroscopic binary star; the shut companion is a white, however
a lot fainter, F star that’s nonetheless burning hydrogen in its core.
Moreover, there may be one other F star and its
companion farther out, so Dubhe is definitely a four-star system.   

One fascinating facet word: NASA’s Wide Field Infrared Explorer (WIRE) telescope launched in 1999 with the meant aim of observing galaxies. However when a technical subject ended WIRE’s major mission prematurely, the small monitoring telescope was repurposed for asteroseismology, measuring the brightness variations of stars to probe their inside construction. Astronomers thus salvaged some helpful science out of an in any other case failed mission. One of many stars the satellite tv for pc noticed was Dubhe, and the findings helped to refine measurements of its mass.

/ Mythology

Perseids crossing Ursa Major
A composite picture of Ursa Main streaked with Perseids: The lip of the Large Dipper is just below the bear’s ear; the tip of its deal with is on the tip of his tail.
Alex Conu

It might be tough to discover a group of stars with extra
widespread recognition and enchantment than the Large Dipper. However of us with even a
slight information of astronomy will recall that the Large Dipper — beloved although
it could be — will not be a real constellation; it’s an asterism, a sample
amongst a smaller group of stars, inside Ursa Main, the Nice Bear. The identify Dubhe
is derived from Arabic for “the again of the bear,” aptly describing the star’s location
inside its constellation.

For the Greeks, the constellation was the bear Callisto (sure,
the identical Callisto that’s the namesake of the Galilean satellite), of which Homer wrote,
the Bear…turns spherical and spherical the place it
is, going through Orion, and alone by no means dipping into the stream of Oceanus
…” That’s
a really poetic means of claiming that Ursa Main is circumpolar when considered from

Ursa Major from Urania's Mirror
Ursa Main from Urania’s Mirror

The idea of Ursa Main as a bear is frequent worldwide, however the
Large Dipper has had a number of completely different interpretations all through time. It’s been
a plow, a ladle, a consuming gourd, a coffin, a wagon, oxen, and others. Within the
Ojibwe tradition of the Nice Lakes area in the US, the celebs of the
Large Dipper had been recognized as a fisher — a small weasel-like mammal — known as ojiig.

to See Dubhe

As Dubhe kinds one of many corners of the Large Dipper’s “bowl,” it couldn’t be simpler to seek out. When trying on the Large Dipper in an upright orientation, Dubhe is the star to the upper-right—one of many two “pointer” stars that cleared the path to Polaris. (The opposite pointer is Merak.)

Big Dipper
The Large Dipper at twilight
Daniel Johnson

With a declination of about 61°, Dubhe is circumpolar for a lot of the U.S, which means it by no means units however rotates constantly within the northern sky all 12 months lengthy. Due to this, the Large Dipper could seem on its facet and even the other way up at numerous occasions all through the night time and the seasons. Nevertheless, Dubhe, together with Merak, won’t ever be removed from the north celestial pole, making it easy to find.

The colour of stars isn’t all the time simple to detect. Hues are sometimes refined, and it takes a little bit of observe to study what it’s you’re in search of. Dubhe is an effective instance to check out. A DSLR digital camera on a tripod may also document Dubhe’s refined orange coloration, in addition to provide the probability to match it with the opposite Large Dipper stars at leisure. Good luck!

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