Since the invention of the telescope, we have been able to "see" further away and study stars and galaxies, as well as many of the more mysterious objects in our Universe. Cosmology is the study of the overall structure of the universe. The observable universe is the universe that reveals itself through electromagnetic radiation that can be detected on Earth.
The Big Dipper constellation is one of the
best known and easiest star asterisms in the night sky to find with the unaided
eye. In some countries the asterism is also known as the Plough. It is actually
a grouping of the seven brightest stars in the Ursa Major constellation. Five of
those stars make up the bulk of the Ursa Major Moving Group. Since two of the
stars are moving in the opposite direction of the other five, the look of the
Big Dipper constellation will reverse in about 50,000 years.
The Big Dipper constellation is made up of seven stars. Alkaid, Mizar, Alioth,
and Megrez make up the handle while Dubhe, Merak, and Phecda round out the bowl
of the dipper. Mizar is actually a binary star. It is a 2nd magnitude star
coupled with a 4th magnitude named Alcor. The two are often referred to as the
Horse and Rider and are separated by a mere 12 minutes of arc. Mizar, at a
distance of 78 light years from the Sun, and Alcor at 81 light years, are
members of the nearest star cluster to the Sun, the Ursa Major moving cluster (Collinder
Not only do the stars within the Big Dipper constellation have some interesting
stories of their own; they also can help you to find other stars and deep space
elements. Polaris is found by imagining a line from Merak to Dubhe and then
extending it for five times the distance between the two Pointers. Extending a
line from Megrez to Phecda, on the inside of the bowl, will lead you to Regulus
and Alphard. If you pull out your telescope and follow a line from Phecda to
Megrez and continuing on for the same distance again, you will find the Hubble
The Little Dipper is a lesser known name for the Ursa Minor
constellation. It is better known as the Little Bear. It is one of the
constellations originally identified by Ptolemy and is still one of the 88
modern constellations. The Little Dipper is also the current location of the
celestial North Pole.
Polaris is the bright star at the end of the handle. Kochab, Pherkad, and Yildun
are three of the stars that make up the bowl of the Little Dipper. The stars in
the bowl are unusual because they are of second, third, fourth and fifth
magnitude. They provide an easy guide to determining what magnitude stars are.
Ursa Minor was said to have been a bear with a tail that was lengthened from
what is usually expected, because of its being held by the tail and spun around
the pole. Ursa Minor and Major were linked by the Greeks to the myth of Callisto
and Arcas. One variation of the story puts Bootes as Arcas and Ursa Minor was
considered to be a dog. This explains the length of the tail and the older name
of Cynosura (the dog’s tail) for Polaris.
The Little Dipper can be seen faintly year-round. Each day it rises in the East
and sets in the West, like the Sun. Throughout the year, the Little Dipper
slowly circles around Polaris counterclockwise. Each season, it is in a
different position. Face north as you look at the night sky. In the winter, the
bowl of the Little Dipper looks like it is resting upright on a table. In the
spring, it appears to be balanced on its handle. The Little Dipper is upside
down throughout the summer. In the fall, its handle points up, and the bowl is
balanced on its side.
The constellation Ursa Minor contains the group of stars commonly called the
Little Dipper. The handle of the Dipper is the Little Bear's tail and the
Dipper's cup is the Bear's flank. The Little Dipper is not a constellation
itself, but an asterism, which is a distinctive group of stars.
The most famous star in Ursa Minor is Polaris, the North Star. This is the star
that is nearest to the North Celestial Pole. If you stood at the north pole,
Polaris would be almost directly overhead. If you can spot Polaris in the sky,
you can always tell which way is north. In addition, the angle of Polaris above
the horizon tells you your latitude on the Earth. Because of this, Polaris was
the most important star for navigating at sea.
To find Polaris, first find the Big Dipper. If you follow the two stars at the
end of the cup upwards, the next bright star
you will run into is Polaris. The distance to Polaris on the sky is about five
times the angle between the two stars at the end of the cup of the Big Dipper.
Because they are so useful for finding the all-important North Star, these two
stars are known as the Pointer Stars. They are also called Dubhe and Merak
(Merak is at the bottom of the cup).
Because the Earth's axis is precessing (like a spinning top wobbles around),
Polaris is only temporarily at the North Pole. In about 14,000 years, Vega will
be the North Star and another 14,000 years after that, it will be Polaris again.
Precession is caused by the the gravitational attraction of the Sun and the
Moon. It only happens because the Earth is not quite spherical.
The Big Dipper is an asterism
that makes up part of the constellation of Ursa
Major (The Big Bear). It is seen here at the
lower left of the image.
The Little Dipper, part
of the constellation of Ursa Minor (The Little
Bear), is seen at the upper right. Polaris, the
North Star, is at the end of the handle of the
The Big Dipper constellation
is made up of seven stars. Alkaid, Mizar, Alioth,
and Megrez make up the handle while Dubhe,
Merak, and Phecda round out the bowl of the
dipper. Mizar is actually a binary star. It is a
2nd magnitude star coupled with a 4th magnitude
The two are often referred to as
the Horse and Rider and are separated by a mere
12 minutes of arc. Mizar, at a distance of 78
light years from the Sun, and Alcor at 81 light
years, are members of the nearest star cluster
to the Sun, the Ursa Major moving cluster (Collinder
The two stars at the end of the bowl of the Big
Dipper, Merak and Dubhe, are called the "Pointer
Stars" because a line drawn between them points
The Big Dipper and Polaris play an important
part in the story of the Underground Railroad
which helped slaves escape their captivity in
the southern states of the United States before
the Civil War by fleeing north to Canada.
The folk song "Follow the Drinking Gourd"
(another name for the Big Dipper) was a coded
song that gave directions on the escape route
from Alabama and Mississippi. While traveling on
their long escape journey, they could always
tell which way was north by the location of
Polaris which they could find by the pointer
The Big Dipper is a circumpolar asterism for
most of the United States. This means it stays
above the horizon all night long as it
apparently rotates slowly counterclockwise
during the night around Polaris due to the
Earth's rotation. It is also comprised of very
bright stars in an easy-to-locate pattern. The
Little Dipper, on the other hand, is comprised
of fairly faint stars that do not really stand
out, except for second-magnitude Polaris.
Polaris, Alpha Ursae
Minoris, commonly North Star,
Northern Star or Pole Star, also
Lodestar, is the brightest star
in the constellation Ursa Minor.
It is very close to the north
celestial pole, making it the
current northern pole star. Many
recent papers calculate the
distance to Polaris at about 434
light-years from Earth.
is 126 light-years from Earth
and is slightly less bright than
Polaris. It is a 2.08 orange
giant star, 16 degrees from
Polaris. Kochab is 2.5 light
years from the Sun, and is 130
times more luminous than the
Sun, at a surface temperature of
Pherkad is located in
the Little Dipper constellation.
It is approximately 480
light-years from Earth and is of
spectral class A3, meaning it
has a surface temperature of
7,500 to 11,000 kelvins. It is
classified as a Delta Scuti type
variable star, is 1100 times
more luminous than the Sun, and
possesses a radius 15 times that
of the Sun.
is a greenish star in the middle
of the tail of the Little Bear
(see image right). It is a white
main-sequence star in the
constellation Ursa Minor. At 172
light-years away, it shines at
an apparent visual magnitude of
4.35. It is moving through the
Galaxy at a speed of 15.8 km/s
relative to the Sun. Its
projected Galactic orbit carries
it between 24,100 and 27,100
light years from the center of
al Farkadain, aka Zeta
Ursae Minoris, is a star in the
constellation Ursa Minor. It has
the traditional name Akhfa al
Farkadain. Zeta Ursae Minoris is
a white stellar class A-type
main sequence star approximately
380 light-years from Earth.
al Farkadain, aka Eta
Ursae Minoris, is a star in the
constellation Ursa Minor. It has
the traditional names Anwar al
Farkadain. Eta Ursae Minoris is
a yellow-white F-type main
sequence dwarf with an apparent
magnitude of +4.95, making it
visible to the naked eye. It is
approximately 97.3 light-years
aka Beta Ursae Majoris is a star
in the northern circumpolar
constellation of Ursa Major. It
has the traditional name Merak.
The apparent visual magnitude of
this star is +2.37, which means
it is visible to the naked eye.
It is more familiar to northern
hemisphere observers as one of
the "pointer stars" in the Big
Dipper. Extending an imaginary
straight line from this star
through the nearby Alpha Ursae
Majoris (Dubhe) extends to
Polaris, the north star.
aka Alpha Ursae Majoris, is one
of the pointer stars that point
to the North Star. It's a yellow
giant star about 123 light years
away. It's 100 times brighter
than the Sun and the brightest
star in Ursa Major (The Big
Dipper). Dubhe can be viewed
year round in the Northern
Cepheus is a constellation in
the northern sky. It is named after Cepheus,
King of Aethiopia in Greek mythology.
Alpha Cephei, traditionally
called "Alderamin", is a white hued star of
magnitude 2.5, 49 light-years from Earth. Beta
Cephei, traditionally called "Alfirk", is a
double star with a blue-hued giant primary of
magnitude 3.2 and a secondary of magnitude 7.9.
Gamma Cephei, traditionally
called Errai, is an orange-hued star of
magnitude 3.2, 45 light-years from Earth. Its
traditional name means "the shepherd". It is a
binary star approximately 50 light years away
There are several other prominent variable stars
in Cepheus. One is Cephei, also known as
Herschel's Garnet Star due to its deep red
color. It is a semi-regular variable star with a
minimum magnitude of 5.1 and a maximum magnitude
of 3.4. The star is around 11.8 AU in radius (AU
- astronomical unit is a unit of length defined
as 92,955,807.273 miles exactly, or roughly the
distance between the Earth and the Sun). If
Cephei were placed at the centre of our
System, it would extend to the orbit of Saturn.
Camelopardalis is a large but
faint constellation in the northern sky. Located
in the part of the celestial sphere facing away
from the galactic plane. Many distant galaxies
are visible within its borders. NGC 2403 is a
galaxy in the M81 group of galaxies, located
approximately 12 million light-years from Earth.
It is classified as being between an elliptical
and a spiral galaxy because it has faint arms
and a large central bulge. NGC 2403 was first
discovered by the 18th century astronomer
Draco is a constellation in the
far northern sky. Its name is Latin for dragon.
Draco is circumpolar* for many
observers in the northern hemisphere. *A
circumpolar star is a star that, as
viewed from a given latitude on Earth, never
sets (never disappears below the horizon), due
to its proximity to one of the celestial poles.
Circumpolar stars are therefore visible from
said location towards nearest pole for the
entire night on every night of the year (and
would be continuously visible throughout the day
too, were they not overwhelmed by the Sun's
Ursa Major (Latin: "Larger
Bear"), also known as the Great Bear, is a
constellation visible throughout the year in
most of the northern hemisphere. It can best be
seen in April. It is dominated by the widely
recognized asterism* known as
the Big Dipper or Plough, which is a useful
pointer toward north, and which has mythological
significance in numerous world cultures. *An
asterism is a pattern of stars
recognized on Earth's night sky. It may form
part of an official constellation, or be
composed of stars from more than one. Like
constellations, asterisms are in most cases
composed of stars which, while they are visible
in the same general direction, are not
physically related, often being at significantly
different distances from Earth. The mostly
simple shapes and few stars make these patterns
easy to identify, and thus particularly useful
to those learning to familiarize themselves with
the night sky.
Vega is one of three
brilliant stars that divide the
northern heavens into rough
thirds, the others Arcturus and
Capella, and with Altair and
Deneb forms the great Summer
Triangle, lying at its
northwestern apex. At magnitude
zero (0.03), it is the sky's
fifth brightest star, falling
just behind Arcturus and just
ahead of Capella. It is also one
of the closer stars to the
Earth, lying just 25.0 light
is one of the most distant stars
you will see with your eye
alone. That’s because it’s one
of the most luminous stars in
the Milky Way galaxy. The exact
distance to Deneb is unclear,
with estimates ranging from
about 1,425 light-years to
perhaps as much as 7,000
light-years. Whatever its exact
distance, when you gaze at
Deneb, know that you are gazing
across thousands of light-years
The best estimates for Deneb’s
distance likely are those
obtained by the Hipparcos Space
Astrometry Mission in the 1990s.
A simple calculation from
initial Hipparcos data gives the
figure of 3,230 light-years,
whereas the refined data yield
just over 1,400 light-years. At
any of these estimates
distances, Deneb is
one of the farthest stars the
unaided human eye can see. It is
so far, that the light that
reaches the Earth today started
on its journey well more than
1,000 years ago.
for us to see it at its enormous
distance, Deneb must also be
tremendously bright and
energetic. Among the 20
brightest stars, only Rigel in
Orion surpasses Deneb in
intrinsic brightness. Deneb is
an A2Ia star, which says that it
is white hot (A2) and a
supergiant star (Ia). Prof.
James Kaler, using the figure of
2,600 light years as the
estimated a diameter 200 times
greater than our sun,
and about a quarter of a million
times brighter in visible light.
Considering its spectral
classification (A2), Deneb must
have a surface temperature
between about 8500 to 9000
kelvins (roughly 14,800 to
15,700 degrees F).
Red Giant Star:
Towards the end of a star's
life, the temperature near the
core rises and this causes the
size of the star to expand. This
is the fate of the Sun in about
5 billion years. Stars convert
hydrogen to helium to produce
light (and other radiation). As
time progresses, the heavier
helium sinks to the center of
the star, with a shell of
hydrogen around this helium
center core. The hydrogen is
depleted so it no longer
generates enough energy and
pressure to support the outer
layers of the star. As the star
collapses, the pressure and
temperature rise until it is
high enough for helium to fuse
into carbon, i.e. helium burning
begins. To radiate the energy
produced by the helium burning,
the star expands into a Red
Majoris (Red Hypergiant)
is the largest known star in the
universe. It is 2000 times the
diameter of the Sun, and the Sun
is 109 times larger than the
Earth. The size of VY Canis
Majoris, think of a passenger
airplane flying along the
surface of this star at
approximately 550 miles per
hour, it would take 1100 years
to circle it one time. Yet, it
is only a tiny dot among several
hundred billion stars forming
our Milky Way galaxy and there
are a hundred billion galaxies
The Big Dipper is an asterism (a small pattern of stars seen in the sky but not officially a constellation) located within Ursa Major. It is made up of seven stars which include – Alkaid, Alcor/Mizar star system, Alioth, Megrez, Phecda, Merak and Dubhe. All of these stars are essential in making The Big Dipper an asterism as they are some of the brightest stars in the Northern Hemisphere.
Top 10 Brightest Stars
Sirius also known as the Dog Star, is the brightest star in the sky. Its name comes from the Greek word for scorching. 8.6 Light-years from Earth.
Canopus is the second brightest star in the sky. 74 LY from Earth.
Rigel Kentaurus also known as Alpha Centauri, is the third brightest star in the sky. 4.3 LY from Earth.
Arcturus is the brightest star in the constellation Bootes, which is one of the oldest constellations in the night sky. It is the 4th-brightest star in the entire sky and 34 light-years from Earth.
Vega is the fifth brightest star in the sky. Its name comes from the Arabic for the swooping eagle. Vega is about 25 light-years from Earth.
Capella is the sixth brightest star in the sky. Capella is a yellow giant star, like our own sun, but much larger. It is 41 light-years away.
Rigel is the seventh brightest star in the sky, Rigel's name is from the Arabic for foot, indicating its place in the constellation Orion. It is a blue supergiant and part of a 4 star system. It is 1400 light years from Earth.
Procyon is the eighth brightest star in the night sky. It is a yellow-white star and at 11.4 light years, one of the closer stars to Earth.
Achernar is the ninth brightest star in the night sky. It is a bluish-white supergiant star that is about 69 light years from Earth.
Betelgeuse is the tenth brightest star in the sky. It is a red supergiant about 13,000 times brighter than our sun and over 1000 times larger. If you placed Betelgeuse in the place of our sun, it would extend past the orbit of Jupiter. Betelgeuse is 1400 light-years from Earth.
Orion's Belt Stars: Alnitak, Alnilam, Mintaka. All are super giant stars, 800, 1000, and 900 light-years from the Earth, respectively. All are a white-blue color and 20 times the mass of the Sun.
Gliese 580.2 is a white main-sequence star in the constellation Ursa Minor. At 83 light years away, it shines at an apparent visual magnitude of 5.15. The star's age is estimated to be 3 billion years old.
RR Ursae Minoris is a red giant star in the constellation Ursa Minor, 458 light years away.
Eta Ursae Minoris is a white main-sequence star in the constellation Ursa Minor. At 97 light years away, it shines at an apparent visual magnitude of 4.95. Eta Ursae Minoris is the primary component of a multiple-star system. The star's age is estimated to be 1.7 billion years old.
Pherkad is a white giant star in the constellation Ursa Minor. At 486 light years away, it is the 175th brightest star in the Earth's sky. Pherkad Minor is an orange giant star in the constellation Ursa Minor. At 398 light years away, it shines at an apparent visual magnitude of 5.02. Pherkad Minor has one confirmed planet known to date (Dec. 2012).
Epsilon Ursae Minoris is a yellow giant star in the constellation Ursa Minor, 303 light years away.
Theta Ursae Minoris is an orange giant star in the constellation Ursa Minor, 846 light years away.
HR 5334 is a red giant star in the constellation Ursa Minor, 428 light years away.
5 Ursae Minoris is an orange giant star in the constellation Ursa Minor, 359 light years away.
HR 5139 is an orange giant star in the constellation Ursa Minor, 411 light years away.
Yildun is a white main-sequence star in the constellation Ursa Minor, 172 light years away.
Zeta Ursae Minoris is a white main-sequence star in the constellation Ursa Minor, 369 light years away.
4 Ursae Minoris is an orange giant star in the constellation Ursa Minor, 455 light years away.
19 Ursae Minoris is a blue main-sequence star in the constellation Ursa Minor, 617 light years away.
Thuban also known by its Bayer designation Alpha Draconis is a star (or star system) in the constellation of Draco. A relatively inconspicuous star in the night sky of the Northern Hemisphere, it is historically significant as having been the north pole star in ancient times.
Kochab aka Beta Ursae Minoris is the brightest star in the bowl of the "Little Dipper" (which is part of the constellation Ursa Minor), and only slightly fainter than Polaris, the northern pole star and brightest star in Ursa Minor. This is a giant star with a stellar classification of K4 III. It is 130 times more luminous than the Sun. Kochab has reached a state in its evolution where the outer envelope has expanded to 42 times the girth of the Sun. This enlarged atmosphere is radiating 390 times as much luminosity as the Sun from its outer atmosphere at an effective temperature of 4,030 K. This heat gives the star the orange-hued glow of a K-type star.
Alkaid is the end star in the handle of the Big Dipper (100 light-years away), the great asterism that makes most of the grand constellation Ursa Major, the Greater Bear. Just fainter than Dubhe, Alkaid is the third brightest star in the constellation and places number 35 in the list of brightest stars. Alkaid is 100 light years away and has a surface temperature of about 20,000 degrees Kelvin. It is one of the hotter stars that can be seen with the naked eye, and glows a soft blue-white color. Alkaid's mass is six times that of the Sun and over 700 times more luminous. Were Alkaid our Sun, we would have to be 25 times farther away to survive, almost to the orbit of Neptune.
Mizar is a quadruple system of two binary stars in the constellation Ursa Major and is the second star from the end of the Big Dipper's handle (78 light-years away). With normal eyesight one can make out a faint companion just to the east, named Alcor or 80 Ursae Majoris. Mizar and Alcor together are sometimes called the "Horse and Rider."
Alioth is a white sub-giant star in the constellation Ursa Major. At 83 light years away, it is the 34th brightest star in the Earth's sky.
Megrez is a white main-sequence star in the constellation Ursa Major. At 80 light years away, it is the 238th brightest star in the Earth's sky.
Phecda is a topaz yellow star in the Great Bear (83.2 light-years away). It is part of "the Big Dipper" stars, a bucket shaped figure or asterism on the back of the Bear, outlined by the stars: Merak and Dubhe.
Dubhe is a pointer star in the constellation Ursa Major (123 light-years away) and the brightest of the seven stars that form the Big Dipper, with apparent magnitude 1.8. Dubhe and Merak form the outer side of the Dipper's bowl, with Dubhe being the upper of the two stars. A straight line extending northward from these pointer stars leads to the North Star, Polaris.
Merak (Beta Ursae Majoris) is a pointer star in the constellation Ursa Major. Based upon parallax measurements of this star, it is located at a distance of 79.7 light-years from the Earth.
Alkaid, is a brilliant white star on the tail of the Great Bear. The Big Dipper wheels high across the north on winter nights. It's low in the northeast in early evening, standing on its handle, and high in the northwest at first light. It's led by Dubhe, the star at the outer edge of the bowl, with Alkaid, the star at the end of the handle, bringing up the rear.
In the mythology of the sky, though, leaders and followers are all a matter of perspective. Alkaid, for example, is an ancient Arabic name that means "the leader." It represented the leader of a group of daughters -- the stars of the dipper's handle -- who were leading a platform containing a dead body.
Regardless of whether it's the leader or the tail, though, Alkaid is an impressive star. It's about six times as massive as the Sun, and when you add up all forms of energy, it's close to a thousand times brighter.
The star's great heft revs up the nuclear engine in its core, so Alkaid "burns" through its hydrogen fuel far more quickly than the Sun does. That makes the surface of Alkaid thousands of degrees hotter than the Sun. It also means that Alkaid will live a much shorter life than the Sun -- about a hundred million years, compared to more than 10 billion years for the Sun.
One other item of note about Alkaid is its distance: almost exactly 100 light-years. That means the light you see from Alkaid tonight actually left the star a century ago - around the start of 1911. stardate.org
There's only one sun in our sky, but for many other worlds, that's not the case. Most of the stars in the galaxy are systems of two stars or more. So any planets orbiting these stars have more than one sun. And if anyone lives on these planets, their concepts of day and night might be quite different from our own.
Consider Dubhe, the star at the top right corner of the bowl of the Big Dipper. Although our eyes see only a single point of light, the system actually consists of at least four stars.
The stars form two close pairs. The more prominent pair includes the star that's visible to the unaided eye. It's a stellar giant -- it's much bigger and brighter than the Sun. It's also much cooler, so it looks orange. The companion star isn't as big or bright, but it's impressive nonetheless -- a hotter star that shines pure white.
These stars are a little closer together than the planet Neptune is to the Sun. So if any planets orbit either star, they'd experience a cycle of day and night quite unlike our own. Sometimes, they'd have two bright suns in the sky, sometimes just one, and sometimes none. There would be times of year when one sun would rise as the other sets, meaning there would be no night at all.
The other pair of stars in the system would be too far to shine as true suns. But they'd punctuate the sky as dazzling points of light, whirling around each other every six days -- adding to the drama of the skies day and night.
Most of the time, the stars that form a "connect-the-dots" pattern in the sky aren't related to each other -- they just happen to line up in the same direction in our sky.
One exception is the five stars in the middle of the Big Dipper -- Mizar, Alioth, Megrez, Phad, and Merak. They're all about the same distance from Earth -- about 80 light-years. And they're moving in the same direction and at about the same speed. What's more, a lot of other stars in that region of the sky are moving along with them.
All of these stars are members of the Ursa Major Moving Group -- Ursa Major because that's the constellation to which the Big Dipper belongs.
All of these stars were probably born about 500 million years ago, from a single vast cloud of gas and dust. They formed a large star cluster. As they orbited the center of the Milky Way galaxy, though, the cluster was slowly pulled apart. Stars closer to the center of the Milky Way moved a little faster than those farther away, stretching the cluster into a long streamer of stars.
Today, the stars are too widely spread to form a cluster -- their gravity no longer binds them to one another. But not enough time has passed to disperse them through the galaxy. So the stars still move through the galaxy in the same way -- forming a wide but rapidly spreading group.
The two stars at the ends of the Big Dipper aren't members of the group, so they go their own way. stardate.org
M46 and M47
On a February night in 1771, comet hunter Charles Messier was scanning to the east of Sirius, the brightest star in the night sky, when he discovered two star clusters. One was small and faint, while the other was larger and contained more bright stars. Messier added them to his list of objects that might be mistaken for comets. And today, the clusters are still best known by Messier's catalog numbers: M46 and M47.
The clusters are in good view this evening, not far to the left or lower left of Sirius, which is well up in the southern sky as darkness falls.
Under dark skies, well away from city lights, M47 is just visible as a hazy patch of light a little smaller than the full Moon. But you really need binoculars to get a good view of both clusters.
M47 contains several dozen stars, including some that are red giants -- old, bloated stars that are in the final stages of life. Such stars are quite bright, which is one reason that M47 is prominent in our sky. Another is that it's fairly close as clusters go -- about 1600 light-years.
M46 is about three times farther, so it doesn't look as impressive. In fact, though, it contains several hundred stars, including several that are quite hot and bright. Such stars burn out fairly quickly, so their presence tells us that the cluster is only a few hundred million years old. stardate.org
Have you ever wanted to find the Big Dipper – known as the Plough in the U.K. or, in Hindu astronomy Saptarishi, after the seven rishis – but just couldn’t spot this famous pattern? Then today’s night sky chart (above) is for you. It shows the Big Dipper on an evening in March, ascending in the northeast during the evening hours. See the Dipper shape? In the early evening in March, the handle of the Dipper is pointing down toward the horizon as it rises. If you are blessed with a dark sky – and have eagle-eye vision – you may be able to see the faint star Alcor next to Mizar, the middle handle star.
The two outer stars in the Bowl of the Big Dipper always point to Polaris.
Still not sure the Pattern you’ve found is the Dipper? Try to notice if the pattern you see matches the chart shown at right. That chart shows a well-known trick for finding the North Star, or Polaris. That is, the two outermost stars in the bowl of the Big Dipper point to Polaris. Those stars are Dubhe and Merak. They are well known among amateur astronomers as The Pointers. If you extend a line about five times the distance between Dubhe and Merak from the star Dubhe – and don’t find a medium-bright star (Polaris) – then the pattern you see is not the Big Dipper. Keep looking.
An ancient eye test for those wishing to join the Roman army involved spotting stars in the handle of our modern-day Big Dipper. You can take this ancient eye test, too.
Go outside around 9 p.m. You should see the Big Dipper just off the northeast horizon. The middle star in the handle of the Big Dipper is Mizar. If you look for a couple seconds longer, you may see a little starry point right next to Mizar. This star is called Alcor. If you had lived in the time of the early Romans and could see Alcor, you would have been eligible to be an archer in the Roman army. If not, you likely would have served in another capacity for the Caesar. It’s said that sultans of the past also tested their soldiers’ eyesight in this way.
Mizar (brighter) and Alcor (fainter) as seen from Earth. Image Credit: ESO Online Digitized Sky Survey
Mizar and Alcor form a “visual double” star. At one time, astronomers doubted that Mizar and Alcor were gravitationally bound to one another. But Mizar is now thought to be four stars in one, and Alcor two stars in one. Given that Mizar and Alcor likely revolve around each other, that makes for six stars in an intricate gravitational dance.
As darkness falls, look for the Big Dipper and the star Mizar in the northeast sky. With either the unaided eye or binoculars, seek for Mizar’s nearby companion: Alcor. ~ from earthsky.org