问MongoDB聚合查询$match在日期范围内不返回任何内容，为什么？

EN

    var start       = moment.utc('03-02-2012').startOf('day');
    var end         = moment.utc('03-02-2012').add('days',1).startOf('day');

    PriceHourly.aggregate([
        { $match: { date: { $gt: start, $lt: end } } },
        { $group: { _id: null, avgPrice: { $avg: '$price' } } }

    ], function(err, results){
        console.log(err, results);
    });

// Model
var PriceHourlySchema = new Schema({
    created: {
        type: Date,
        default: Date.now
    },
    full_date: {
        type: String,
        required: true,
        trim: true
    },
    day: {
        type: String,
        required: true,
        trim: true
    },
    hour: {
        type: String,
        required: true,
        trim: true
    },
    price: {
        type: Number,
        required: true
    },
    date: {
        type: Date,
        required: true
    }
}, 
{ 
    autoIndex: true 
});