Name the physical quantities which remain constant in a planetary motion (in elliptical orbits).

Explanation

To answer the question regarding the physical quantities that remain constant in planetary motion in elliptical orbits, we can break down the solution into the following steps:

### Step-by-Step Solution:

1. **Understanding Kepler's Laws**:
- Kepler's laws describe the motion of planets in elliptical orbits around the Sun. There are three laws: the law of orbits, the law of areas, and the law of periods.

2. **Kepler's First Law (Law of Orbits)**:
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