Question

Predict how the Moon would appear to an observer in space during its revolution. Would phases be observable? Explain.

Short answer

No, phases wouldn't be observable; the Moon appears fully illuminated or not, depending on the observer's location relative to the Sun.

Step-by-step solution

Understanding Phases from Earth

On Earth, we see the Moon go through a cycle of phases including new moon, crescent, first quarter, gibbous, full moon, and then back again. This cycle occurs because we are viewing the Moon from Earth as it orbits our planet.

Considering the Observer's Perspective in Space

An observer in space, far from Earth and the Moon, would have a different vantage point. This observer would see both Earth and the Moon continuously lit by the Sun, except for the parts in shadow.

No Phases from the Observer's View

To the observer in space, the Moon wouldn't go through traditional 'phases' like it does for an Earth-based observer. This is because there's no shifting perspective with respect to the lighted and shadowed portions of the Moon as seen from this space vantage point.

Determining Visibility Changes

While the observer wouldn't see phases, the visibility of the Moon's surface can vary slightly depending on the specific position in space relative to the orbital paths of Earth and the Moon. However, these would not be 'phases' as defined by the changing visibility of the illuminated part of the Moon's surface.

Key concepts

Moon's orbit

The Moon's orbit is a fascinating elliptical path it follows around the Earth. As the Moon travels this journey, different amounts of its lighted surface become visible to us on Earth. This orbit takes approximately 27.3 days to complete a full circle around our planet.

One key thing to understand is that the Moon is always half-lit by the Sun. The phases we observe are due to the angles of the Sun, Earth, and Moon changing as the Moon orbits Earth.

• The Moon's orbit is slightly tilted – about 5 degrees – relative to the Earth's orbital plane around the Sun. This tilt prevents us from having a lunar eclipse every month.
• This orbit is also responsible for creating the changing "phases" of the Moon over time, as seen from our perspective on Earth.

observer perspective

Viewing from Earth, the Moon changes in appearance as it moves. An observer from space, however, has a different experience. If positioned at a great distance where both the Moon and Earth are visible, the observer would not witness phases.

They would see the Moon consistently illuminated by the Sun unless it enters Earth's shadow, during a lunar eclipse. This perspective is due to the observer's different vantage point.

• In space, there's no shifting view between night and day on the Moon — only a constant half-lit sphere.
• The only "changes" visible might be due to distance or orbital position but not phases.

visibility changes

Although phases are not observed from space, changes in visibility occur. The observer might notice parts of the Moon's surface becoming less or more visible but this doesn't equate to phases.

The differences arise primarily because of relative positions in space rather than varying illumination from the Sun. For example:

• A slight shift in position might obscure some surface features while revealing others.
• The direct sunlight illumination remains constant, highlighting the Moon's vast craters and plains.

These visibility shifts occur subtly, primarily based on viewing angle, not illumination change.

Earth from space

Seeing Earth from space provides a unique perspective that contrasts significantly with our experience on the ground. From this vantage point, both Earth and the Moon are subject to constant sunlight on one half, with the other draped in shadow.

From afar, Earth presents as a vibrant globe of blues, greens, and white clouds, while the Moon appears as a greyish sphere. This perspective showcases the contrast between both bodies:

• Earth, with its diverse biosphere, displays dynamic weather systems and changing cloud patterns.
• The Moon remains more static, with its surface marked by ancient craters and low albedo.

Understanding these views can illuminate the space observer's experience, highlighting the persistent interactions of light and shadow between these celestial bodies.