请以{"star_name": "", "distance_from_earth_in_light_years": "", "constellation": "", "size_comparison": ""}格式分别介绍太阳，北极星，天狼星
user
{
  "star_name": "太阳",
  "distance_from_earth_in_light_years": "0",
  "constellation": "不适用",
  "size_comparison": "太阳的直径约为1.39百万公里，是地球直径的约109倍"
},
{
  "star_name": "北极星",
  "distance_from_earth_in_light_years": "430",
  "constellation": "小熊座",
  "size_comparison": "北极星的直径约为太阳的37倍"
},
{
  "star_name": "天狼星",
  "distance_from_earth_in_light_years": "8.6",
  "constellation": "大犬座",
  "size_comparison": "天狼星的直径约为太阳的1.7倍"
}
assistant