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Related Concept Videos

Nuclear Fusion02:45

Nuclear Fusion

The process of converting very light nuclei into heavier nuclei is also accompanied by the conversion of mass into large amounts of energy, a process called fusion. The principal source of energy in the sun is a net fusion reaction in which four hydrogen nuclei fuse and ultimately produce one helium nucleus and two positrons.
A helium nucleus has a mass that is 0.7% less than that of four hydrogen nuclei; this lost mass is converted into energy during the fusion. This reaction produces about...
Conservation of Angular Momentum: Application01:18

Conservation of Angular Momentum: Application

A system's total angular momentum remains constant if the net external torque acting on the system is zero. Examples of such systems include a freely spinning bicycle tire that slows over time due to torque arising from friction, or the slowing of Earth's rotation over millions of years due to frictional forces exerted on tidal deformations. However in the absence of a net external torque, the angular momentum remains conserved. The conservation of angular momentum principle requires a change...
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Kepler's First Law of Planetary Motion

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No object with a finite mass can travel faster than the speed of light in a vacuum. This fact has an interesting consequence in the domain of extremely high gravitational fields.
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Radiation Pressure: Problem Solving

The radiation pressure applied by an electromagnetic wave on a perfectly absorbing surface equals the energy density of the wave. The wave's momentum also gets transferred to the surface when an electromagnetic wave is entirely absorbed by it. The rate at which momentum is transmitted to an absorbing surface perpendicular to the propagation direction equals the force on the surface.
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Experimental System of Solar Adsorption Refrigeration with Concentrated Collector
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Experimental System of Solar Adsorption Refrigeration with Concentrated Collector

Published on: October 18, 2017

Is the sun shrinking?

I I Shapiro

    Science (New York, N.Y.)
    |April 4, 1980
    PubMed
    Summary
    This summary is machine-generated.

    Analyzing 23 Mercury transits from 1736-1973 revealed no significant solar diameter change. Earth-based angular diameter decrease is under 0.3 arc seconds per century, contradicting previous findings.

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    Last Updated: Jun 24, 2026

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    Area of Science:

    • Astronomy
    • Solar Physics
    • Historical Observations

    Background:

    • Direct solar diameter measurements have yielded conflicting results.
    • Historical transit observations offer an alternative method for assessing solar variability.

    Purpose of the Study:

    • To investigate long-term changes in the Sun's diameter using historical Mercury transit data.
    • To compare findings with previous studies based on direct solar observations.

    Main Methods:

    • Analysis of 23 Mercury transits recorded between 1736 and 1973.
    • Regression analysis to determine the rate of change in the Sun's angular diameter as observed from Earth.

    Main Results:

    • No statistically significant change in the Sun's diameter was detected.
    • A decrease in angular diameter of less than 0.3 arc seconds per century was calculated (90% confidence limit).
    • This result contradicts Eddy's finding of a 2 arc seconds per century decrease.

    Conclusions:

    • Historical Mercury transit data suggest the Sun's diameter has remained stable over the observed period.
    • The findings challenge previous claims of significant solar diameter contraction based on direct measurements.