大熊座全年在北半球大部分地区都能看到，在北半球中纬度以上呈环极状。从南温带纬度地区看，主星群是看不见的，但仍然可以看到星座的南部。
Right Ascension: 10.67 hours赤经：10.67小时
Declination: + 55.38 degrees赤纬： + 55.38 度
Visible: between latitudes +90o and -30o可见： 纬度 +90o 和 -30o 之间
Best viewed: at 21:00 (9 p.m.) during April最佳观赏时间：4月21：00（晚上9点）
大熊座位于北半球的第二象限（NQ2），其邻近的星座是Bootes、Camelopardalis、Canes Venatici、Coma Berenices、Draco、Leo、Leo Minor和Lynx。北斗七星的明亮星星标记着天熊的尾巴和后躯。
大熊座
大熊座属于大熊座家族，还有Bootes、Camelopardalis、Canes Venatici、Coma Berenices、Corona Borealis、Draco、Leo Minor、Lynx和Ursa Minor。
北斗七星可以在一年中的不同时间在天空的不同部分找到。在春季和夏季，北斗七星和小北斗七星的头顶都更高，而在秋季和冬季，它们更接近地平线。规则是，弹起和落下。
北斗七星的外观随着季节的变化而变化。在秋天，它在晚上停在地平线上，而在冬天的晚上，手柄似乎悬挂在碗上。在春天，它在晚上倒置，在夏天，碗向地面倾斜。
许多深空天体与北斗七星位于同一天空区域。其中一些深空天体是：北斗七星控制下的漩涡星系，风车星系 - 即使用双筒望远镜也可以找到，双星温内克4，螺旋星系博德星系，不规则的雪茄星系，行星状星云Messier 97 - 猫头鹰星云，或螺旋星系Messier 108和Messier 109。
Big Dipper Guide to Other Stars北斗七星其他星星指南
北斗七星星群可以作为寻找其他明亮恒星的指南。北斗七星手柄的弧线通向大角星，天熊饲养员，天体牧民布特斯星座中最亮的星星。
沿着一条线进一步通向Spica，它是夜空中第17颗最亮的恒星，也是处女座黄道星座中最亮的恒星。标志着北斗七星杯的两颗恒星通向北极星，即现在的北极星，然后揭示了北斗七星的星群。另一对恒星，Megrez和Phecda，为狮子座黄道星座中最亮的恒星轩辕十四和天空最大星座九头蛇中最亮的恒星阿尔法德指明了道路。
小熊座
从梅格雷兹到杜布赫的线指向御夫座的卡佩拉，从梅格雷兹到梅拉克的一条线指向双子座黄道星座的卡斯特。
Big Dipper Stars北斗七星
从我们在地球上的角度来看，形成北斗七星星群的明亮恒星彼此相对接近。其中一些星星是夜空中最亮的星星之一。
Alioth阿利奥特
阿利奥特，被指定为Epsilon Ursae Majoris，是大熊座中最亮的恒星，也是北斗七星中最亮的一颗。Alioth是星群手柄的第三颗恒星，最接近碗，比它的大多数邻居要亮得多。
Alioth also shares the 31st place as the brightest star in the night sky with Alnitak – one of three stars that make up the Orion’s Belt asterism.
还与构成猎户座腰带星群的三颗恒星之一 Alnitak 并列夜空中最亮的恒星第 31 位。
Alioth Orion's Belt asterism （阿利奥斯·猎户座腰带星群）
Alioth是一颗蓝白色巨星或亚巨星，具有奇特的光谱，其中含有钙K线。它距离地球86光年，比我们的太阳亮102倍。
Alioth的视星等为1.77，它也被归类为Canum Venaticorum变星 - 这意味着，由于其磁场和化学特性，它的亮度会发生变化。Alioth的质量是太阳的291%，半径约为太阳的414%。它的磁场是地球的100倍。
Alioth-Dubhe-and-Alkaid
Alioth、Dubhe和Alkaid是被选中进行天体导航的58颗导航星之一。只有最亮、最容易识别的恒星才属于这一组。
Dubhe杜布
Dubhe，被指定为大熊座阿尔法星，是大熊座中第二亮的恒星。它也是一个光谱双星系统，是夜空中第33颗最亮的恒星，与英仙座中最亮的恒星米尔法克共享这个称号。
杜布和Merak被称为指针星，用于寻找北极星（目前是北极星）。主星Dubhe A是一颗橙色巨星，视星等为1.79。
Dubhe距离我们大约123光年，它的亮度大约是太阳的316倍。Dubhe 比 Alioth 暗约 2%
DUBHE位于北斗七星星群的碗中。
Merak
Merak, designated as Beta Ursae Majoris, is the fifth brightest star in Ursa Major, having an apparent magnitude of +2.37. It is a bluish-white subgiant star that has exhausted its hydrogen supplies, and thus it has begun to cool down.
Merak is 270% more massive than our Sun, having 300% of its radius, and it generates enormous amounts of energy, being 63.015 times brighter than our Sun. Merak is one of the four stars which form the bowl of the Big Dipper.
Merak is located at around 79.7 light-years away from us, and it is part of the loose open cluster named the Ursa Major Moving Group. Since Alkaid and Dubhe aren’t part of the Ursa Major Moving Group, they will eventually lead to the Big Dipper’s dissipation in the course of the next several thousands of years.
Phecda
Phecda, designated as Gamma Ursae Majoris, is an Ae star, which is surrounded by an envelope of gas that is adding emission lines to its spectrum.
Phecda is the sixth brightest star in Ursa Major, having an apparent magnitude of 2.4. The star is located at around 83.2 light-years away from us.
Phecda is white hydrogen fusing dwarf, having 294% of our Sun’s mass, and 304% of its radius. It is 65 times brighter than our Sun. This star is a fast spinner, having a rotational velocity of around 178 km / 110.6 mi per second.
Phecda is one of the stars forming the Big Dipper’s bowl and the Great Bear’s hindquarters, it is the lower-left or southernmost star of the Big Dipper’s bowl.
Megrez
Megrez, designated as Delta Ursae Majoris, is the dimmest of the seven stars in the Big Dipper asterism, having an apparent magnitude of +3.31. It is the 11th brightest star in Ursa Major.
Megrez is a hydrogen-fusing dwarf still on the main sequence, located at around 80.5 light-years away from us. This star has 163% of our Sun’s mass, 140% its radius, and it is around 14 times brighter.
Megrez is a young star, having an estimated age of 300 million years. It rotates even faster than Phecda, having a rotational velocity of around 233 km / 144.7 mi per second.
Megrez is the 11th brightest star in Ursa Major, the upper left star of the Big Dipper bowl, connecting the bowl to the handle, formed by the brighter Alioth, Mizar, and Alkaid.
Mizar
Mizar, also designated as Zeta Ursae Majoris, is a quadruple star system with a combined magnitude of 2.04. It is located at around 82.9 light-years away from us.
Mizar is the fourth brightest star in Ursa Major. The primary star is a blue-white hydrogen fusing dwarf, which has around 220% of our Sun’s mass, and 240% its radius.
Mizar is 33.3 times brighter than our Sun, and it is the first telescopic binary star discovered, this discovery took place in 1908.
Mizar is the middle star of the Big Dipper’s handle and it forms a naked-eye double with Alcor, a fainter binary star located at a separation of about 12 arcminutes. It is the fourth brightest star in Ursa Major.
Alkaid
Alkaid, designated as Eta Ursae Majoris, is the third brightest star in Ursa Major, and also the 38th brightest star in the night sky, sharing the title with Sargas.
Alkaid is a blue main-sequence star located at around 103.9 light-years away from us. It was once one of the 15 Behenian Fixed Stars – a group of stars used in medieval times in magic rituals.
Alkaid is 594 times brighter than our Sun, having 340% its radius, and around 610% of its mass. Alkaid’s spectrum has served since 1943 as one of the stable anchor points by which other stars are classified. It is an X-ray emitting star with broadened absorption lines in its spectrum due to its rapid rotation ( 150 km / 93.2 mi per second ).
Its fast rotation results in its equatorial radius being bigger than its radius at the poles, leading to temperature variations. Some other stars which appear to share this trait, are Vega or Achernar.
Alkaid is the leftmost star of the Big Dipper’s handle, also marking the Great Bear’s celestial tail.
The Future
The stars of the Big Dipper will be at different locations in around 50,000 years or so. This will result in the asterism changing its shape and facing the opposite side.
However, the Big Dipper asterism will continue to be visible, and not greatly deformed, for more than 100,000 years from now on.
Did you know?
In England and the United Kingdom, the Big Dipper is known as the Plough. The symbol of the Starry Plough has been used as a political symbol by Irish Republican and left-wing movements.
In the Finnish language, the asterism is sometimes called by its old Finnish name, Otava. The meaning of the name has been almost forgotten in Modern Finish, it means salmon weir.
The ancient Romans knew the seven stars as the “seven plow oxen” or Septentrio, with only two of the seven stars representing oxen and the others forming a wagon pulled by the oxen.
A couple of Native American groups saw the bowl as a bear and the three stars of the handle as either three cubs or three hunters following the bear.
In Slavic languages and Romanian, the Big and Little Dipper are known as the Great and Small Wagon, while the Germans know the Big Dipper as the Great Cart.
Sources:
Image Sources:
https://legendsofthestars./uploads/1/7/5/0/17509023/2794715_orig.jpg
https:///wp-content/uploads/Fujii-Big-Dipper-Labeled_900x713_v2-757x600.jpg
https://i./originals/83/c2/da/83c2dab13fcb083bac9075581133de80.jpg
https://www./wp-content/uploads/2017/09/Megrez-in-Ursa-Major.jpg
https://www./wp-content/uploads/2017/08/Alkaid-Eta-Ursae-Majoris.jpg
https:///wp-content/uploads/2017/10/behenian-star-glyphs.jpg
