# RA, DEC and J2000 Explained

> What those numbers on your certificate mean — and how to read them.

Right ascension (RA) and declination (DEC) are longitude and latitude on the celestial sphere — together they pin down any star. J2000 is the reference epoch (noon of January 1, 2000): because of precession coordinates drift, so quoting them in J2000 keeps every observatory speaking the same language.

URL: https://astarnamed.com/guides/ra-dec-j2000 · Category: astronomy · Published: 

## The sky’s grid

- **Declination** — 0° at the celestial equator, ±90° at the poles
- **Right ascension** — 0–24h eastward from the equinox
- **Example (Regulus)** — RA 152.09296° · DEC +11.9672°

## What J2000 is

Earth’s axis wobbles like a spinning top (precession), one full circle every ~26,000 years. That means “where the celestial equator is” changes over time, so astronomers pin all coordinates to one instant — J2000, noon on January 1, 2000 (Julian day 2451545.0).

## What this means for your certificate

The certificate and 3D star page carry exactly these coordinates: RA (J2000) and DEC (J2000). Type them into any planetarium app (Stellarium, for instance) and it points to your star. Combined with Sky View’s live compass, it can even tell you where to look tonight.

## FAQ

**Why hours for RA but degrees for DEC?**

RA is tied to Earth’s rotation, so 24-hour notation maps directly to “when it is visible”; DEC is an angle measured north/south of the equator.

**Look Up the Coordinates of That Moment ✦** — https://astarnamed.com/find

> See the real star data behind every memorial star → https://astarnamed.com/our-data

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# 赤经、赤纬与 J2000 详解

> 证书上那串坐标是什么?怎么读?

赤经(RA)与赤纬(DEC)是天球上的经纬度,可唯一定位任何恒星。J2000 是坐标基准历元(2000 年 1 月 1 日正午):因为岁差,坐标会缓慢漂移,统一用 J2000 才能让全世界的天文台说同一种语言。

## 天空的经纬网

- **赤纬 DEC** — 天赤道为 0°,向南北各 ±90°
- **赤经 RA** — 从春分点向东 0–24 小时
- **示例(轩辕十四)** — RA 152.09296° · DEC +11.9672°

## J2000 是什么

地球自转轴像陀螺一样缓慢摆动(岁差),约 26,000 年一圈。这意味着"天赤道在哪里"会随时间改变。天文学家因此把所有坐标锚定在同一个时刻——J2000(2000 年 1 月 1 日正午,儒略日 2451545.0)。

## 和你的证书有什么关系

证书与 3D 星页印的就是这套坐标:RA (J2000)、DEC (J2000)。拿着它们在任一星图软件(如 Stellarium)中检索,就能定位到你的星。配合 Sky View 的实时方位提示,它甚至能告诉你今晚该往哪里看。

## FAQ

**为什么赤经用"小时"而赤纬用"度"?**

赤经与地球自转同步,用 24 小时制方便换算"何时可见";赤纬是角度,沿天赤道向南北量度。

**查回那一刻的坐标 ✦** — https://astarnamed.com/find

> 看每一颗纪念星背后的真实星表数据 → https://astarnamed.com/our-data