# Astronomers use coordinate systems to plot the position of stars in the night sky

Astronomy questions and answers – Looking up into the night sky you probably wonder how ancient stargazers were able to navigate using the stars in the night sky as their guide. One of the first things ancient stargazers did to help them navigate the night sky and the surface of the Earth was to create a coordinate system to pinpoint relative positions of the stars in the night sky in relation to one another.

Looking upward into the night sky, imagine the sky above you as a sphere of infinite size, centered on the Earth. This technique works in general because distances to the stars above you is not discernible using your naked eye, so the objects you see above you in the night sky all appear to lie on a great sphere at an infinite distance in relation to you.

Modern astronomers use two coordinate systems to determine the relative positions of objects in the night sky; the altitude-azimuth coordinate system and the equatorial coordinate system. We will talk a little about both coordinate systems currently being used by modern astronomers to help them plot the positions of the objects they view in the night sky and using celestial objects you view on your “Journey to the Beginning of Space and Time” to navigate your way through the universe.

In the altitude-azimuth coordinate system, altitude indicates the number of degrees from the horizon to the object in the night sky you’re viewing and ranges from 0 degrees at the horizon to 90 degrees at the zenith above you. Modern astronomers measure azimuth along the horizon from north to east, to the point where a line passing through the object in the night sky intersects the horizon at a right angle, and azimuth varies between 0 degrees and 360 degrees. Astronomers also subdivide each degree of azimuth into 60 arcminutes and each arcminute into 60 arcseconds, which helps to further subdivide the immense distances between each degree of measurement in the night sky.

The altitude-azimuth coordinate system doesn’t take into account the rotation of the Earth, though, and astronomers have solved this problem by fixing coordinates to the celestial sphere you imagine above you in the night sky. Celestial cartographers have created “celestial globes”, similar to the globes of the Earth that cartographers have devised for centuries to show the Earth and all of its features. On these celestial globes, you’ll find terms like the celestial equator and North and South celestial poles.

In the equatorial coordinate system, astronomers use two aspects called declination and right ascension to fix a star’s position on the celestial sphere you picture above you. Declination is analogous to Earth’s latitude and represents the angle between the object you’re viewing in the night sky above you and the celestial equator. Declination varies between 0-90 degrees, North and South of the celestial equator, and is measured in degrees, arcminutes, and arcseconds while a minus sign is used to designate objects south of the celestial equator.

The lines of circles that run through the celestial poles perpendicular to the celestial equator represent the hour circle of objects in the night sky above your head and are analogous to the meridian of longitude on the Earth. In order to fix an object’s position in the celestial sphere above you, we’ll also need to set the zero point of the longitude coordinate of the object, which astronomers call the object’s right ascension. In order to accomplish this, we need an intersection point between the Earth’s equator and its orbital plane, the ecliptic. Astronomers call this intersection point the vernal equinox and the sun appear to travel through the intersection point annually around March 21, as it moves South to North crossing the celestial equator.

The angle that lies between the vernal equinox and the point where the hour circle of the celestial object in question intersects the celestial equator is the right ascension of the object you see in the night sky. Right ascension is measured in hours (h), minutes (m), and seconds (s), from west to east, and the vernal equinox is zero-hour. There are about 24 hours in each day on the Earth, so each hour of right ascension in the night sky corresponds to 15 degrees of longitude.

The movement of the Earth and the objects in the night sky above you mean the appearance of the night sky is dynamic in nature, so celestial objects will appear to circle the celestial poles as you watch the night sky. A star with a greater distance from a celestial pole than your latitude will only be visible to you during a portion of its orbit. In this case, the star will rise in the east and set in the west. Stars that are always above your horizon are circumpolar for your latitude and you’ll see these stars for their entire orbit.

The Earth’s rotation and the movement of the stars also mean the constellations in the night sky above you travel slowly westward during the year. Pinpoint a star you know well in the night sky at exactly 9 P.M. tonight. This same star will be in the exact same position in the night sky tomorrow night, only 4 minutes earlier, at 8:56 P.M. Check the time this same star is in the same position on the next night and you’ll see this occurs at 8:52 P.M.

Do a little math and you’ll verify that in one month this set up would leave the stars in the night sky 2 hours out of phase with our first positional reading in the night sky for this same star. In 3 months, generally one season, the stars in the night sky above you will have traveled a quarter of the way across the night sky. After four seasons, this would bring the star in question back to the same position in the night sky as twelve months before.

One way to estimate distances in the night sky above you and give yourself a tool to help you navigate the universe on your “Journey to the Beginning of Space and Time” is to use star pairs in the night sky as your guide. Star travelers can learn by using star pairs in the Big Dipper, for example.

Check out this astronomy site at http://astronomytonight.yolasite.com/, and then let me know what you think?

Learn how NASA astronomers are planning on detecting extraterrestrial moons orbiting distant suns https://spaceshipearth1.wordpress.com/2013/12/31/searching-for-extraterrestrial-moons/.

Take a look at the latest natural color images taken by the Cassini spacecraft https://spaceshipearth1.wordpress.com/2013/12/22/cassini-spacecraft-show-views-of-the-solar-system-in-natural-color/.

# Astronomy Products

## Viewing the universe using two eyes allows you to see more

Astronomy Products – Binoculars are a useful and fun way to view the solar system and delve even deeper into the cold darkness of space and time. The modern astronomer makes use of an amazing array of scientific viewing devices and techniques in the human journey to the beginning of space and time”. Large telescopes on both the Earth and orbiting the planet search the cosmos on a daily basis, using advanced optical systems, and new techniques to look at the universe in ways never before experienced by humans. Thousands of amateur star-gazers also use similar optical systems and techniques based on the same equipment to view the universe on a nightly basis. Good viewing binoculars, however, are a great and fun way for casual stargazers to journey to nearby celestial objects to have a quick look, and they’re also a good way to tour the universe.

Why bother with binoculars considering the array of sophisticated viewing equipment available for the dedicated amateur astronomer? Binoculars have a few points in their favor that make them good for the casual stargazer. Binoculars have a low power and wide field of view that makes them an ideal time-machine-to-the-stars for casual viewers of the night sky, or even sophisticated viewing of the universe. Science has certainly proven that viewing the night sky with two eyes is better than viewing the universe with one. The human eye’s power of resolution and ability to detect faint objects in the night sky dramatically improves using two eyes, rather than the one required for viewing with the traditional telescope. In addition, color perception and contrast of the view humans’ observe using two eyes, rather than one, improves noticeably.

### Astronomy binoculars will enhance the view during your journey

Need more proof? On a clear, moonless night, head out to your favorite deep sky viewing spot to conduct a little test of your own. Once you arrive, keep both eyes open, while covering one eye with your hand, and take a look at the night sky. Make a mental note of the faintest stars you see in the night sky. Now, take your hand away from the eye you have kept covered and view the same area of the night sky as before, and you’ll see a lot more stars in the area you previously viewed. It isn’t unusual for some stargazers to experience as much as a 10-percent improvement in perception using two eyes, rather than one, and this can be just the difference that provides some viewers on a casual journey to the beginning of space and time” with a life-changing experience.

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Learn why astronomy binoculars are a popular choice with amateur astronomers

Read about astronomers viewing a supernova they think might have given birth to a black hole

# Journey to Red and Orange stars in September’s night sky

## Fall is in full bloom in the Northern Hemispheres of planet Earth and lovers of the reds, oranges, and bright reds on the leaves of fall will enjoy the rich, warm and colorful hues in the night sky of September and October.

Astronomy News – If you’re heading out into the wild to enjoy Mother Nature’s bounty at this time of year? After a day walking through the forest watching the leaves on the trees turn color, from drab green to mixed shades of yellow, orange, and red. Take the time to lay back on the cold ground or your sleeping bag and check out the colors in the night sky. Even better, set up your binoculars or time machine to the stars, and enjoy the colors in the night sky by taking a journey to the beginning of space and time.”

Stargazers have witnessed the colorful displays in the night sky for generations and our ancestors surely spent many a night staring upwards in wonder at the various colors they could see in the night sky. It was 19th-century Irish astronomer John Birmingham, who first made note of the colorful hues of light in the night sky. His ideas and the thoughts of Danish astronomer Hans Schjellerup, who had compiled a catalog of red stars in 1866, were mentioned in Birmingham’s work “The Red Stars: Observations and Catalog”. This catalog contains a total of 658 red and orange stars colorful enough to delight the human senses and make your imagination dance a lively step.

Reading the introduction of Birmingham’s catalog of red and orange stars, one notes he mentions a region of space and time he refers to as “The Red Region”. This region includes parts of the Milky Way Galaxy, between Aquila, Lyra, and Cygnus, that are filled with orange and red stars that will make the eyes dance and entice the human imagination to create possibilities beyond anything we as humans have imagined.

## The colors of astronomy in September are a highlight amateur astronomers will love

September is the perfect time for you to board your time machine to the stars and journey to the beginning of space and time to experience the Red Region. The Red Region will be well above the southern horizon once the sun goes down. This region of space and time has eye-gems for stargazers to view in September, with reds and oranges that will make lovers of fall smile, and turn up their color sensitivity. The colorful stars in the Red Region warm sequentially through spectral classes: G (yellow), K (orange), M (red) and rare carbon class C (deep red). Astronomers have subdivided star classes from 0 to 9, with a G9 star being a little closer to orange than yellow, and a K5 star having a color somewhere between orange and red.

All-star gazers will see varying hues of red, orange, and yellow during their journey to the beginning of space and time that will depend on each star gazers own particular biology. In fact, we all view color slightly differently, so individual star gazers shouldn’t rely on a star’s spectral class for a visual clue to a star’s true color. Take, for example, the strikingly colorful, double star Albireo (Beta Cygni) in Cygnus. Stargazers through the centuries have described its magnitude 3.1 K3 primary star as yellow, topaz, gold and orange. Its magnitude 5.1 B9 (blue-white) secondary star (34″ away) on the other hand, has been described as deep-blue, azure, sapphire and even green.

The perception of color for humans is subjective and depends on varying individual parameters that can also be a product of physiological and psychological effects, such as the strong contrasting colors of a double star, like Albireo. The colors star gazers view through their time machine to the stars can also be obscured by dust and pollutants in the air, which will redden a star’s color. Stars that are low on the horizon, in comparison to higher stars, will also appear redder to viewers, just like the sun turns redder as it falls toward the horizon.