Conference is on the Yom Kippur holiday After doing well at science fair, I started working with an extremely nice professor at the local university who encouraged me to submit my work to the relevant conference. I was rejected at large, but accepted to one of the workshops. The workshop is the day before the conference. The professor reviewed my paper twice, probably taking him a half hour or hour total (it's a short paper). He also told the conference he would shepherd me, which kind of puts his name on all of this. However, looking at the calendar to plan my flight etc, I noticed the workshop is on the day of Yom Kippur! I am not that religious, and if this was some huge event for me I could possibly make an exception, but I'm not sure if presenting my mediocre work (the work is good for a high school student, but really lame for an actual conference) to the few people who will come to the presentation supersedes such a holiday. Also, after being rejected I didn't really want to go anyway, since I won't understand most of the presentations and I feel they only accepted me to the workshop to encourage me since I'm a student.

How do I talk with the professor and the conference/workshop about my problem? It is completely my fault!

Side note: who schedules an academic event on Yom Kippur? That's like scheduling it on Christmas or Easter!

Follow-up: I decided to go. I'm just not sure what it's like submitting to a workshop of a conference but not the conference at large.
Unless you're presenting joint work and had worked out your attendance with your coauthors in advance, not attending a conference is always your choice.

Not attending a conference for religious reasons is also completely standard and understandable. (Though your claim that Yom Kippur is just like Christmas is a bit unconvincing.  83% of Americans identify as Christian, whereas 1.4% identify as Jewish.  Moreover, a lot of Americans who identify as Jewish do not fast/atone on Yom Kippur and would be happy to attend a conference on that day: I do and I would.  Though not with as much glee as I would attend a conference on Easter, I admit.) I think it's an A-class excuse: i.e., if you tell this to your faculty advisor he will accept it without any comment.  I would keep to yourself however the fact that your amount of Jewishness is enough to get you out of a conference that you view as inferior but not a really important one.  That's not the most mature perspective, and if in your later life people observe that you seem to be using religion as an excuse to improve your schedule, they will not be so thrilled with you.  

By the way, I would think that there would be a lot of other reasons that a high school student could not fly to attend a conference.  Saying "Sorry, I've just learned that my schedule doesn't allow me to attend" ought to already be more than sufficient (B+? A-?). 

I think you may be off in your appraisal of the situation and the opportunity that going to any part of an academic conference is for any high school student.  My advice would be to, when you say that you can't go to this conference, tell your advisor that you really appreciate the mentorship and would be eager to go to a different conference, possibly a bit later on and/or during the summer.

Finally, your faculty advisor does indeed sound extremely nice.  Academics are extremely busy, and quality mentorship takes time and energy.  Your estimate that he spent half an hour looking at two drafts of your paper sounds rather naive to me unless he explicitly told you that.  I would spend more than 15 minutes looking at a student's cover letter, let alone their paper.  By the way, the fact that he is willing to spend the time probably means that he thinks you are extremely talented, so I hope you do not give up too easily.