Observing the Sun and Planets
Watch the Solar System from Earth: observe the Sun safely, follow the planets along the ecliptic, and learn the words for planet positions like opposition, transit and occultation.
Get the method right under pressure
Free interactive practice on the steps that lose marks under exam pressure.
Start revising freeWhat you'll cover
Watching the Solar System
Topic 5 is about observing the Solar System from Earth: how the Sun and planets move across our sky, how to watch the Sun safely, and the words astronomers use for planet positions. Let us start with the key terms.
Key terms
Learn these before you begin:
Ecliptic terms
- Ecliptic
- Zodiacal Band
- Retrograde motion
- Radiant
- The Sun's yearly path across the sky
- The band of sky where the planets are seen
- A planet appearing to move backwards
- Where a meteor shower appears to come from
Observe the Sun safely
Never look directly at the Sun: it can permanently damage your eyes. To observe it safely, use pinhole projection: make a small hole in card and let the Sun shine through it onto a second card, forming a projected image you can look at safely.
Safe observation
What is the safe way to observe the Sun in the specification?
- Pinhole projection onto a card
- Looking through binoculars
- Staring at it near sunset
- Reflecting it into your eye with a mirror
Match each observation term to its meaning
- Conjunction
- Opposition
- Transit
- Occultation
- A planet appears close to the Sun in the sky
- A planet lies opposite the Sun, best for viewing
- A planet passes across the Sun's face
- One body passes in front of and hides another
Backwards planets and meteors
Usually planets drift slowly eastward against the stars. Sometimes an outer planet seems to stop and move westward for weeks: this is retrograde motion, caused by Earth overtaking it in orbit. Meteors are streaks of light from small particles burning up in the atmosphere. In a meteor shower, many appear to spread out from one point, the radiant.
Observing planets
Select the TWO true statements about observing planets.
- At opposition, an outer planet is well placed for viewing all night
- Retrograde motion is a planet appearing to move backwards for a time
- A transit is when a planet hides a distant galaxy
- The ecliptic is the path of the Moon only
Observation terms frame
When a planet lies opposite the Sun in our sky, it is at _____. When it passes across the Sun's face, that is a _____. The Sun's yearly path across the sky is the _____. A meteor shower seems to spread out from its _____.
At opposition
A planet is at opposition. Where is it compared with the Sun?
- Opposite the Sun, so it rises as the Sun sets
- Right next to the Sun, lost in its glare
- Passing directly across the Sun's face
- Below the horizon all night
Motion and meteors frame
A _____ is a streak of light from a particle burning up in the atmosphere. During _____ motion a planet appears to move backwards. The narrow band of sky holding the planets is the _____ Band. Two markers on the ecliptic are the First Points of Aries and _____.
Name the position
Classify each planet position.
- A planet passes directly across the face of the Sun. This is a...
- An outer planet lies opposite the Sun and is up all night. It is at...
- The Moon moves in front of a star and hides it. This is an...
Apply what you know
Apply what you have learned about safe observation and planet motion.
- To look at the Sun safely, you should...
- A planet appears to move backwards against the stars for a few weeks. This is...
- Meteors in a shower appear to come from one point called the...
Explain what you have learned
Explain how you can observe the Sun safely, and describe what retrograde motion of a planet looks like from Earth.
- Describe the safe method (pinhole projection)
- Say why you must not look directly at the Sun
- Describe what retrograde motion looks like from Earth