|
||||||
 |
Recent Posts | Search by username | |
Contact Us | |
Login | |
Register |
 |
 |
|||||
 |
 |
 |
 |
 |
 |
|
24HourForums.com > Supported Forums > Brian's Science & Nature Shack > Astronomy Terms and Definitions |
| Moderated by: Brian |
|
|||||||||||||||||||||||||||||||||||||||
| Author | Post | |||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Aquila Original500© Member 
|
  |
|
||||||||||||||||||||||||||||||||||||||
|
Once again we have come to a spectacular time of the year when seasonal change starts to sweep across the northern hemisphere. Blustery days with tree leaves streaking across the sky. Cooler days, and most notably, less sunlight. which brings us here to our first term and definition. Autumnal Equinox – Occurs about September 23, is the Suns position as it crosses the celestial equator going south. At equinoxes, day and night are equal in length. The moment when the Sun can be observed to be directly above the equator. The 2006 autumnal equinox is on September 23 at 12:03 am (all times in Eastern Daylight Time). For the Northern Hemisphere. Did You Know... In Japan, the Autumnal Exuinox is a time for visiting the graves of loved ones and honoring one's ancestors. ::magicdude::
|
||||||||||||||||||||||||||||||||||||||||
| ||||||||||||||||||||||||||||||||||||||||
|
24HourNut Administrator  Body pillows rock!
|
|
|
||||||||||||||||||||||||||||||||||||||
|
Cool beans ::alien::
 The best human beings start good new topics and vote on the better posts. |
||||||||||||||||||||||||||||||||||||||||
|
Aquila Original500© Member
|
|
|
||||||||||||||||||||||||||||||||||||||
|
Declination - The stars on the celestial sphere are like cities on the globe. Cities are located on the globe using latitude and longitude. Longitude says how far the city is east or west along the Earth's equator; latitude says how far a city is north or south of the Earth's equator. Declination is like latitude. It reports how far a star is from the celestial equator. To find the declination of a star follow an hour circle "straight down" from the star to the celestial equator. The angle from the star to the celestial equator along the hour circle is the star's declination. From Wikipedia: In astronomy, declination (abbrev. dec or δ) is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Dec is comparable to latitude, projected unto the celestial sphere, and is measured in degrees north and south of the celestial equator. Therefore, points north of the celestial equator have positive declination, while those to the south have negative declination.
A celestial object that passes over zenith, has a declination equal to the observer's latitude, with northern latitudes yielding positive declinations. A pole star therefore has the declination +90° or -90°. Conversely, celestial objects with a declination higher than 90° - φ, where φ is the latitude, are visible the whole sidereal day. Such stars are called circumpolar stars, while the phenomenon of a sun not setting is called midnight sun. Interesting facts about declination and terrestrial navigation. http://www.ngdc.noaa.gov/seg/geomag/jsp/Declination.jsp the above link is to the NOAA geophysical data center where you can calculate your magnetic declination adjustment value. What's this magnetic declination adjustment stuff you say? A declination value represents the error between magnetic North and True North, for a specific location. Declination degree values can be either expressed as Easterly and Westerly, or as positive and negative values. Easterly declinations are represented as positive values, and Westerly declinations are represented as negative values. For example, your current location could be represented as a Westerly declination of 15 degrees, or as a declination value of -15 degrees. Now, let's look at a few examples to help you understand how to use your declination values: EXAMPLE 1 First of all, lets assume you know you current declination value to be -12 degrees (this is the same as 12 degrees Westerly), and you want to be traveling in a true 72 degree path. When you try to determine your current bearing, your compass indicates you are traveling with a bearing of 72 degrees from magnetic north. Knowing your declination value (-12) however, you determine that you are actually bearing a course 60 degrees from True North (compass value + declination value = 72 - 12 = 60). At this point, you realize in order to actually travel 72 degrees from True North you will have to add 12 degrees to your planned bearing, and set your compass to 84 degrees. Now traveling at a bearing 84 degrees from magnetic north, you are actually traveling 72 degrees from True North. EXAMPLE 2 If you have declination value of -20 (this is the same as 20 degrees Westerly), then when your compass indicates you are bearing a 90 degree course, you are actually bearing at 70 degrees. If you really do want to head with a bearing of 90 degrees, you will have to set your compass to a bearing of 110 degrees, to compensate for your local error. EXAMPLE 3 If you have declination value of +10 (this is the same as 10 degrees Easterly), then when your compass indicates you are bearing a 90 degree course, you are actually bearing at 100 degrees. If you really do want to head with a bearing of 90 degrees, you will have to set your compass to a bearing of 80 degrees, to compensate for your local error. Reviewing the above examples you will realize it is important you understand exactly how to use your declination value, as your adjustments are different for determining your current bearing and charting a new bearing. DETERMINING YOUR CURRENT BEARING If you are asking yourself "What direction am I really heading?", you will need to take your compass reading and add your declination value. This is your "True" direction. Meaning, this is your direction with respect to true North. (Remember, if you add a negative number, you are actually subtracting a value) Referencing examples from above? Example 1: 72 + (-12) = 60 Example 2: 90 + (-20) = 70 Example 3: 90 + 10 = 100 SETTING YOUR CORRECT BEARING TO TRAVEL If you are asking yourself "How do I travel a true 120 degrees?", you will need to take your desired heading and subtract your declination value. This will compensate for the error. (Remember, if you subtract a negative number, you are actually adding a value) Referencing examples from above (if you want a true bearing of 120 degrees)? Example 1: 120 - (-12) = 132 Example 2: 120 - (-20) = 140 Example 3: 120 - 10 = 110 Another way to think about this scenario is doing the opposite of your declination value. For example if you declination value is -15, then you will add 15 to the compass bearing to adjust for this error. And if your declination value is +15, then you will subtract 15 from the compass bearing to adjust for this error. ::magicdude:: I'll never get lost again!
|
||||||||||||||||||||||||||||||||||||||||
|
Aquila Original500© Member
|
|
|
||||||||||||||||||||||||||||||||||||||
|
Maybe Declination was a bit lengthy! HA! get lenghty...maybe not so funny...anyway...... I'll bet some of you have heard this term before.  Albedo - The albedo of an object is how much light it reflects, a perfect reflector such as a mirror would have an albedo of 100, the moon has an albedo of 7, and the Earth has an albedo of 36. on certain days my forehead has an albedo of 46. 
|
||||||||||||||||||||||||||||||||||||||||
| ||||||||||||||||||||||||||||||||||||||||
|
librtyhead Original500© Member 
|
|
|
||||||||||||||||||||||||||||||||||||||
|
Man! I was just gonna get one of those 170x binoculars w/tripod! Now I can never look at the stars the same way.............great post! I remember a guy had an 8' telescope in his front yard,he was showing a look to all the kids in the neighborhood.......trouble is it was daytime!My question is is that possible?
|
||||||||||||||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||||||||||||
24HourForums.com > Supported Forums > Brian's Science & Nature Shack > Astronomy Terms and Definitions | ||||||||||||||||||||||||||||||||||||||||
| Site Supporters | |||
|---|---|---|---|
| Posts Of The Day | Mock Forums | WowClassic | |
Themes and most mods done in collaboration with: WowClassic - powerful forum software with the best support service.
We are partners with Forum Owner Services
Powered by - Copyright © 2003-2006 Aycan Gulez
We are partners with Forum Owner Services
Powered by - Copyright © 2003-2006 Aycan Gulez