public class NasaApiResponse
{
    public Collection Collection { get; set; }
}

public class Collection
{
    public List<Item> Items { get; set; }
}

public class Item
{
    public List<Data> Data { get; set; }
    public List<Link> Links { get; set; }
}

public class Data
{
    public string Title { get; set; }
    public string Description { get; set; }
    public DateTime DateCreated { get; set; }
    public string Photographer { get; set; }
    public List<string> Keywords { get; set; }
}

public class Link
{
    public string Href { get; set; }
}