Gemara:

Rosh Hashana 

Halacha:

Tefillah 

Machshava:

Tefillah 

Holidays:

Tu Beshvat 

References: Rosh Hashana: 14A  

Description

Why do we skip Tachanun on ט"ו בשבט? The Gemara explains the significance of the day as one in which "the majority of the rain passed" even though it's still winter for a few good weeks. This seems consistant with our Jewish perspective of being far more EXCITED/CELEBRATING what CAN BE versus WHAT IS/WAS.