Groups Why Join? Astronomy Day. The Complete Star Atlas. Q: Is Polaris visible from any latitude south of the equator? Jim Clark Watauga, Texas. Snapshot : ALMA spots moon-forming disk around distant exoplanet. Ask Astro : Does dark energy create the voids between galaxy clusters?
Looking for galaxies in all the wrong places. Capturing the cosmos: How to be an astrophotographer. Sky This Month : November Chiricahua Astronomy Complex: An observing mecca for amateurs. Neutron stars: A cosmic gold mine. Ask Astro : Can a black hole form without a parent star?
Cosmos: Origin and Fate of the Universe. Astronomy's Moon Globe. Galaxies by David Eicher. Astronomy Puzzles. Think of the long, skinny triangle made by the width of your fist and your eye. Imagine dividing that angle into 60 arcminutes--or arcseconds--tiny angle, eh? Imagine someone holding up a penny there.
If you could see that penny 4 kilometers away, the angle the penny subtends at your eye is one arcsecond. This is the sort of tiny angle that astronomers like to work with. Daily or Diurnal Motion 8 Go back outside and note the motion of the stars.
When you are facing Polaris, which way do the stars appear to go around the celestial north pole? The Earth spins on its north-south axis which gives us day and night.
If all the stars were fixed on the celestial sphere, then as the Earth spun, we would see that during different times of the day, we would see different parts of the sky or different parts of the celestial sphere.
This is illustrated on the right B below. Another way to look at this is if we assumed the Earth was stationary and if we have the celestial sphere rotating about the axis defined by the North and South Celestial Poles. This is in fact what we apparently see when we go outside and view the heavens. We appear to stand on an immobile Earth while all the stars and the Sun rotate around us. Thus the diurnal motion of day and night can be imagined to be due to the rotation of the celestial sphere around the Earth.
This is illustrated on the left A below. It is the apparent rotation of the celestial sphere that results in the Sun and stars rising in the east and setting in the west. The space-age view of the Earth as a "spinning blue marble" make this obvious.
But before the space age it was not so clear. There was little concrete evidence to distinguish which of the following views was reality. A clever way of actually demonstrating the Earth's spin was devised by the French physicist Foucault who hung a huge pendulum that kept swinging for several hours. The pendulum keeps swinging to and fro in its initial direction and the Earth spins underneath.
There is a Foucault pendulum in the Gamow Tower opposite the stadium, across the road from the Ralphie statue on the CU Boulder campus. Apparent Motion of the Stars This link shows you the apparent motion of the stars as viewed from a northern latitude location, at the equator, and a southern latitude location. For each location, we see the motion of the stars in the four cardinal directions: North, East, South, and West. Each animation shows you a winter sky through an entire day, with the Sun and Moon "turned off" so you can watch the stars move.
Annual or Seasonal Motion 10 What do we call the line that passes through the signs of the zodiac? Back to Figure 1. Notice that the ecliptic is tilted with respect to the celestial equator. This is due to the fact that the Earth's axis is tilted From the perspective of a stationary Earth, it would appear that the ecliptic is tilted Note that the Earth's orbit is very close to circular.
Furthermore, the Earth is closest to the Sun in January - which is summer for the southern hemisphere but winter for the north. With an Earth tilted This variation in the elevation of the Sun over the year is the cause of the seasons. The following diagram shows the elevation of the Sun at different times of the year in Boulder. It will be furthest north during the summer solstice; it will be furthest south during the winter solstice.
Polaris shines at 2nd magnitude. On this astronomers' scale, smaller numbers represent brighter objects, with the brightest stars and planets in the night sky at around magnitude zero or even negative magnitudes. The North Star it is a "pulsing" star, a Cepheid variable , which appears to vary in brightness ever so slightly — only one tenth of a magnitude — over a time frame of just under four days.
If you have a small telescope and train it on Polaris, you just might notice a tiny companion star called Polaris B shining at 9th magnitude with a pale bluish tint.
This companion was first sighted by Sir William Herschel in just a year later, Herschel would discover the planet Uranus. Astronomers believe that the two stars — A and B — are separated by about 2, astronomical units — one astronomical unit a. The orbital period of the two stars may number in the many thousands of years. In , by studying the spectrum of Polaris, a third companion star Polaris C was discovered. This one, a white dwarf, lies only Its extreme closeness to the far more brilliant Polaris A explains why it went unseen for so long.
Exactly where you see Polaris in your northern sky depends on your latitude. From New York it stands 41 degrees above the northern horizon, which also corresponds to the latitude of New York. Since 10 degrees is roughly equal to your clenched fist held at arm's length, from New York Polaris would appear to stand about "four fists" above the northern horizon.
At the North Pole, you would find it overhead. At the equator, Polaris would appear to sit right on the horizon. So if you travel to the north, the North Star climbs progressively higher the farther north you go.
When you head south, the star drops lower and ultimately disappears once you cross the equator and head into the Southern Hemisphere. And always keep this fact in mind: Polaris is more accurate than any compass. A compass is subject to periodic variations and can only show you the direction of the lines of the strongest magnetic force for a particular spot and for a particular time.
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