What time is it? The Big Dipper can tell you if you do not have a watch or mobile phone on you!

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What time is it? The Big Dipper can tell you if you do not have a watch or mobile phone on you!

What time is it? The Big Dipper can tell you if you do not have a watch or mobile phone on you!

Since you NOW know where north is, you can use the orientation of the Big Dipper in relation to Polaris to determine the approximate time. Because the Big Dipper is circumpolar, it never rises or sets, but rather rotates around the north celestial pole, marked by the position of Polaris, the North Star. If you watch the position of the Big Dipper through the course of the night, you will notice that it rotates around the pole, counter-clockwise, or bowl-first. The Big Dipper, as with the entire sky, will make one complete revolution about the pole once per sidereal day. The sidereal day is approximately four minutes shorter than the 24-hr. solar day we are more familiar with. For simplicity, we can assume a full 24-hr. period when observing on a single night, but remember that the Big Dipper will be in the same position in the sky approximately four minutes earlier each successive night. When using the Big Dipper to tell time, it is easy to imagine the pointer stars as the hour hand of a one-handed clock, but instead of making two revolutions per day as our clocks do, it makes a single revolution. The pointer stars will appear opposite of their observed position 12 hrs earlier or 12 hrs later; it will appear to make one quarter turn every six hours, traverse 45 degrees of arc in 3 hrs. It's helpful to establish a reference position. Luckily, the timing works out so that the pointer stars are aligned nearly on the meridian at midnight on March 1. You can imagine that at 12 noon on March 1st, the pointer stars will be aligned directly below Polaris. Since we can approximate one complete revolution in 24 hrs, it's easy to imagine the position of the pointer stars at any given hr once you have an initial reference position. Due to the 4 minute difference between the sidereal day & the solar day, the pointer stars will have rotated slightly further to the west at the same hour on each successive night, making a complete revolution over the course of the year. Therefore, each successive month, at the same time, the pointers will be approximately one-twelfth of the way around the pole. Since the pointers are oriented close to the meridian at midnight on March 1st, they will be opposite, or directly below Polaris one-half year later, on September 1. They will be oriented to the left  on June 1, & to the right on December 1. Note that 1 hr of time represents the same angular movement of the pointers as one-half month when viewed at the same time. Now, simply knowing the date and having an unobstructed view of the Big Dipper, you will be able to determine the time. Do not forget to factor in Daylight Savings Time, which will cause the pointer stars to be behind by an hr, or 15° of angle. The closest star cluster. Now that the Big Dipper has told us what direction is north and what time it is, lets learn a little about its stars. While we often refer to the parts of the Big Dipper by their representative names (handle, bowl, and pointer stars), did you know that all 7 stars in the Big Dipper have names? Starting from the end star of the handle and moving along to the back, bottom, & front of the bowl, the stars are named Alkaid, Mizar, Alioth, Megrez, Phecda, Merak & Dubhe. These stars were most likely formed in the same nebula and are all traveling through the galaxy together. This makes the Big Dipper the closest star cluster to us. When visiting the Big Dipper w/ a telescope, a great starting point is Mizar, the middle. This has always been my favorite place to start because Mizar & Alcor were the first objects after the Moon that I learned to find with my 1st telescope. Known in ancient times as the horse and rider, Mizar and Alcor are both spectral type-A stars, so there will not be any notable color contrast, but the close proximity of the two bright stars in a low power eyepiece makes for a pleasing view. Just a bit to the south of the midpoint of the imaginary line connecting Mizar & Alcor lies a 7th magnitude star makes the view a little more interesting. But it doesn’t end there. Mizar itself is a double star, with a 4th magnitude companion 14 arcseconds away, which is an easy split even in small telescopes. Once you have absorbed the view of Mizar and Alcor, you're ready to travel to a distant galaxy, so move your scope from Mizar, through Alcor, and continue along that line about eight times the Mizar-Alcor distance until you reach a 6th magnitude star. This is the first star along a shallow zigzag of four similar magnitude, similarly spaced stars that I call the Mizar-M101 line. Once you reach this star, move your scope in a line roughly parallel to the inner portion of the handle of the Big Dipper, but moving away from the bowl of the Big Dipper. Through a low power eyepiece, the shallow zigzag of the Mizar-M101 line will be easy to spot. You shouldn’t get lost here, but if you do, just back-track to Mizar and Alcor and try again. Once you reach the 4th star in the line, stop, & continue in the same direction you moved when you first left Mizar and Alcor, & for approximately the same distance. If you don’t see a large, diffuse glow in your eyepiece, try moving your eye around the field slowly to see if you can pick it up using averted vision. This is the face-on spiral galaxy M101, sometimes called the Pinwheel galaxy. Face-on galaxies are a little tricky to spot because we are looking at them from over one of their poles, so light from the “disk” of the galaxy is spread over the maximum possible area. For best results, use the lowest magnification available. If sky conditions permit, you may even be able to spot it in an 8 x 100 mm finder. Another spiral galaxy that presents itself as nearly face on to the inhabitants of the Milky Way is somewhat more well known and not too far away (from the perspective of a terrestrial star-gazer). This galaxy lies just across the Dipper’s handle from M101 & is easy to hop to from Alkaid, the very end of the Dipper’s handle. From Alkaid, you’ll want to move the telescope about 2° to the southwest until you come across a 5th magnitude star known as 24 Canes Venaticorum. From this star, make a 120° turn back towards the southeast and travel about the same distance as from Alkaid to 24 CVn. You should find your gaze moving just past a pair of 7th magnitude stars a little less than a degree apart and oriented approximately perpendicular to the vector you arrived from. Nudge the scope just a bit further to the southeast and you should spot not one, but two fuzzy patches of light. This is the double nucleus of the Whirlpool Galaxy, or Messier 51 and NGC 5195. This is one of the most observed and photographed galaxies in the northern sky and once you realize how easy it is to find, you will find yourself taking the brief trip from the end of the Big Dipper’s handle whenever the opportunity presents itself.
The next star hop brings us to the opposite end of the Big Dipper’s handle, that is the star that joins the handle to the bowl, Megrez. This star hop takes us to what is perhaps the least observed Messier object and certainly the most peculiar, as it is the only double star in Messier’s list of 110 objects. From Megrez, move north-northwest in a line parallel to the back side of the bowl. About 1.5° away you should spot a 6th magnitude star. Keep moving in the same direction about one-third of a degree & you'll spot a nice, identical pair of tenth magnitude stars. This is Messier 40. Beginning from the southernmost pointer star Merak, or the bottom-front star in the Dipper’s bowl, we can find two Messier objects on a single trip. On this trek we not only encounter another spiral galaxy, but also the second and final Messier in our adventure that lies within our own Milky Way galaxy. From Merak, move the scope to the southeast two degrees, about one-fourth of the way from Merak to Phecda along the bottom of the Dipper’s bowl, but deviating from that line by approximately 20° of angle below the bowl. Through low power you should spot a trio of stars that appears to me as a greatly enlarged version of the Trapezium in Orion missing one of its stars. The trick here is to imagine where that fourth star would be, and that is where you should spot M97, the Owl Nebula. This is the galaxy M108.
The next star hop is a bit more tricky, but the effort pays off by showcasing what I believe to be one of the finest views in the northern sky. For this star hop, it helps to have a Telrad or red dot finder, because you’re going to aim your scope at an area of sky based on widely-spaced naked-eye guide stars rather than hopping off from one of them. To start, draw an imaginary diagonal line through the bowl of the Big Dipper from the lower back (Phecda) to the upper front (Dubhe). Now extend this line out the same distance as the diagonal through the bowl, but slanted slightly to the north, deviating from the original diagonal line by about 5° of angle. If you point your telescope at this seemingly indistinct patch of sky, you should find the contrasting galaxy pair M81 & M82, once referred to as Bode’s Nebulae. M81 is a bright, textbook-perfect spiral galaxy and M82 is an edge-on irregular galaxy noted for its highly energetic star-forming characteristic, giving it another nickname, the Starburst Galaxy. Using just enough magnification to frame the galaxies with some surrounding sky, the view is unforgettable. I like to view the pair using a 8 mm Nagler eyepiece in my Pronto, which shows just over 1.5° of sky at 53x. Going back to our line diagonally crossing the bowl, move in the opposite direction. Extend this line approximately 60% of the distance through the bowl beyond Phecda, and here you will find galaxy M106. This is one of the brightest galaxies in the region and should be easy to spot. The last star hop should be an easy one as it is a relatively short trip. Move back to Phecda and extend the line marking the bottom of the bowl back away from Merak, only about the distance of the width of the Moon. This is the barred spiral galaxy M109. In conclusion, the Big Dipper has pointed us to 9 Messier objects, which should help guide you if you are planning on doing the Messier Marathon this year. For some observers, Leo is a sign of Spring. For others, it is the rising of Arcturus. For me, the most prominent sign of Spring season has always been the Big Dipper shining bright & high overhead. Enjoy your day, it's almost March 1 and you can do this with YOUR telescope that night, if it's not raining, if it rains, wait 2 days!

Demi Lovato

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