most events like the rising and setting of the Sun were used a natural measurement of time until recently.
Solar time, which is based on the motion of the Sun, is not the only way of measuring time, however. One might keep track of the regular appearance of the full Moon. That event occurs once about every 29.5 solar days. The time between appearances of new moons, then, could be used to define a month.
One also can use the position of the stars for measuring time. The system is the same as that used for the Sun, since the Sun itself is a star. All other stars also rise and set on a regular basis.
Although any one of these systems is a satisfactory method for measuring some unit of time, such as a day or a month, the systems may conflict with each other. It is not possible, for example, to fit 365 solar days into 12 or 13 lunar months exactly. This problem creates the need for leap years
Read more: http://www.scienceclarified.com/Ti-Vi/Time.html#ixzz5e1E705sr
I abbreviated most of it but there is a ton more at this link if you still need more.
Answer:
The symbol is the right answer.
Explanation:
The “ Symbol” is the correct answer because chemist uses the letters of the alphabet to denote the element. For instance, the element oxygen is denoted by the letter of the alphabet “O”, the hydrogen is denoted by the letter of alphabet “H”, Boron is denoted by the letter of alphabet “B”, etc. Here these are the examples that use one letter but there are other elements that use more than 1 letter as the symbol. For example, the Chlorine is represented by the Cl.
Answer:
Explanation
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One
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Ca(OH)2 + 2HNO3 -----> Ca(NO3)2 + H2O
Focus on the NO3. This is an odd problem and you usually do not focus on the complex ion. But this one works easiest if you do.
The problem now is going to be the oxygens. There are 2 with the Calcium and only 1 free one going to the water. (The NO3 has been taken care of in the last step).
Ca(OH)2 + 2HNO3 -----> Ca(NO3)2 + 2H2O
Count the atoms. I think this equation is balanced.
atom Left Right Result
Ca 1 1 Balanced
O 8 8 Balanced
H 2 + 2 2*2 Balanced
N 2 2 Balanced
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Two
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CH4 + O2====> CO2 + H2O
Start with the hydrogens.
The right side requires a 2
CH4 + O2 ===> CO2 + 2H2O
Now look at the oxygens. There are 4 on the right. and only 2 on the left. You need to multiply O2 by 2
CH4 + 2O2 ===> CO2 + 2H2O
Each side has 1 Carbon 4 hydrogens and 4 oxygens. The equation is balanced.
There are 21 atoms represented in the formula :) hope this helped.
