Express when festivity or event happens I need to write an eassy about festivities and I included the following sentence:


  公历每年十二月十五日是这个西方传统的节日。


The teacher said this was not correct Chinese, instead, I should have written:


  圣诞节这个西方传统节日在每年的十二月二十五日。


I also saw other examples in the book.


  圣诞节是在每年的十二月十五日。Festivity + 是在每年的 + date.  中秋节是农历八月五日。Festivity 是 +
  date. 中国的春天一般在一月底到二月初。 Chinese Festivity + 在 date.


So I am a bit confused. From what I learned:

1) It seems that you cannot first put the date and then 的 festivity. 

2) You can put the event and then 是在，是，and 在 and after that, the date. 

Are these two assumptions correct?

Saludos desde España.
Of course you can put the event before or after the date.

When you write the name of an event first, you can add the information of when this event occurs.
Example: [圣诞节] [是在] [十二月二十五日] = [Christmas] [is on] [25th December]

~

When you write a date first, you can add the information of what this date represents
Example: [十二月二十五日] [是] [圣诞节] = [25th December] [is] [Christmas]

More example:
我的生日是在日十二月二十五日 - My birthday is on December 25th.
十二月二十五日是我的生日 - December 25th is my birthday

When you are describing &quot;when the event occurs&quot;, you can omit &quot;在&quot; and write &quot;圣诞节是十二月二十五日&quot; (Christmas is 25th December) or &quot;我的生日是十二月二十五日&quot; (My birthday is 25th December)

When you are describing &quot;what the date represents&quot;, you cannot add &quot;在&quot;  and write  &quot;十二月二十五日是在圣诞节&quot; (25th December is on Christmas) or &quot;十二月二十五日是在我的生日&quot; (25th December is on my birthday )

You can add more information about the date. &quot;十二月二十五日&quot; just means &quot;25th December&quot; ; &quot;每年的十二月二十五日&quot; means &quot;25th December of every year&quot;