Here's how to think about it:
* Short vowels are usually found in words where the vowel is followed by a consonant, like "cat", "dog", or "sun".
* Long vowels can be found in words with a silent "e" at the end, like "bike", "hope", or "time".
In the word "desk", the "e" is followed by a consonant ("s") but it also has a silent "e" at the end, which makes the "e" sound long.