URSA MINOR
(April, May, June, July, August, September and October schedule)

     Ursa Minor constellation is visible on the sky during all year. It is in best position on the sky for evening observing in July, but we will also observe it in April, Maj, June, August, September and October. 

Double and multiple stars

     Alpha Ursae Minoris - Its name is Polaris. It is yellow supergiant star, one of a dozen only yellow supergiants currently discovered and known in our galaxy Milky Way. Its visual magnitude is about 2.0. It is about 430 light years away from the Earth. Its mass is around 6 times bigger than the mass of our Sun, and its diameter is about 45 times larger than the Sun diameter. Its surface temperature is about 6,000 K. Its age is about 70 million years.
     The companion has visual magnitude 9.0 and is separated on the sky about 18 arc seconds  from the main star. It is main sequence star a bit bigger in mass and diameter than our Sun, and a bit hotter. It orbits the main component at a distance of about 350 billion km and probably needs several thousand years for one orbit.
     The spectral analysis revealed another star which is very close to the main component, separated on the sky only 0.2 arc seconds. Too close to be resolved and observed visually with a telescope. It is a main sequence star a bit bigger in mass and equal diameter as our Sun making one orbit around the main component every 30 years at a distance of about 3 billion km. Its visual magnitude is 9.2.
     Polaris currently is located on the sky close to the north celestial pole, and thus is current North Pole star. If we imagine a line which goes through the Earth south pole and the Earth north pole and continue that line towards the sky, it will hit a point on the sky which is very close to Polaris. That point close to Polaris is called celestial north pole. Because of the Earth rotation around its own axis (which is line through the poles), we have impression that the Earth is not moving, but all the sky above our heads is moving. And is moving in a specific way, so that all stars on the sky appear as they move clockwise in a circle around the north celestial pole during the night. In 24 hour period, the Earth will make one rotation of 360 degrees around its own axis, and thus we have impression as all stars on the sky made one rotation of 360 degrees around the north celestial pole and the next night after 24 hours period they appeared on the sky in the same place where they were the previous night. This is the reason why the stars are ''moving'' on the sky - because of the Earth rotation we have impression that the sky and the stars are moving on the sky - they raise over the eastern horizon, move towards west in a circular line and finally set behind the western horizon.
     But nothing in life is simple. This is how the things will get a bit more complicated: There is one important thing we need to take into account - we should not forget the another movement of the Earth - its orbital movement around the Sun - it takes 365 days for the Earth to make one full orbit around the Sun. During the 24 hour period which takes the Earth to make one rotation, it also moved around the Sun a bit. That means after 24 hours period we will not see the stars and the sky exactly on the same place as it was the previous night 24 hours ago! It will take 4 minutes less this to happen! If one star this evening is exactly on the south sky lets say at 22.00 pm, then tomorrow evening that star will be exactly on the south sky at 21.56 pm. Or at 22.00 pm tomorrow evening the star will be a bit west on the sky then it is today at 22.00 pm. So every next night it looks like the whole sky has moved a bit west. That is why we have different constellations on the sky every next month. Every month new constellations appear on the east sky, and every month some constellations disappear bellow the west horizon. This is celestial mechanics - or astromechanics which is part of the astronomy science - it studies the movement of the celestial objects. It also studies the real movement of the planets, stars, galaxies and all other celestial objects. It takes many years until astronomy students learn everything about the celestial mechanics, but we learned quite a bit just now!
     The most important to remember is that because of the Earth rotation around its own axis the stars and the whole sky moves from east toward west in a circular fashion around the Polaris star during the night - that is why I always stress that some particular object at a given time will be in good position for evening observing - because during the night maybe it will not be anymore in good position for observing just because the sky is moving. And also I  sometimes stress that we will try to catch some constellation in the evening - because if it is already on the west sky, it will quickly set behind the west horizon. The Earth rotates once in 24 hours - that means that the sky also must make one rotation for those 24 hours and appears the same the next night at the same time.
     The other most important thing to remember is that because of the Earth orbit around the Sun the sky appears as it has moved during every next night a tiny bit towards west. That means the constellations which are rising on the east sky in spring, during the summer night will be around the zenith, and those who in spring are around the zenith, during the summer night will be close to the west horizon. In fall new constellations will be around the zenith, and in winter again new. The whole picture of the sky will repeat again in the next spring. Because the Earth in 365 days will make one orbit around the Sun, that means the whole sky must also make one full rotation in 365 days, and after 365 days we will see the same picture of the sky. That means after every 365 days we will observe again the same constellations. That is why amateur astronomers like to use the terms spring constellations (those are constellations which in spring in the early evening are in best position for observing because they are visible on the sky around the zenith or high in the sky), summer constellations, fall constellations and winter constellations. That is why we have schedule - because every month some new constellations appear on the sky - that means every month we will observe some new constellations - and during the whole observing season we will have chance to observe all spring, summer, fall and winter constellations visible from the northern hemisphere. 

Deep sky objects
(can be observed only from dark location outside of the city)

     We will not observe any deep sky object from this constellation.