What is the Mercury phase tonight?
Mercury is in the waxing gibbous phase and is 96% illuminated in its phase cycle on January 24, 2025. It appears almost circular in the sky through a telescope. It is 4.8 arcseconds in diameter.
Mercury phases in order
Mercury goes through phases just like the moon.
Mercury takes about 88 days to orbit the sun relative to the background stars, called the sidereal period of Mercury.
However, Mercury takes about 116 days to orbit the sun relative to Earth, called the synodic period of Mercury. Mercury takes the extra time (28 days) as Earth also moves in its orbit.
That’s why Mercury takes about 116 days to travel from one inferior conjunction position (i.e., new phase) to the next inferior conjunction position (i.e., next new phase). This is called a phase cycle of Mercury.
In a phase cycle, Mercury goes through the following phases in order: new Mercury, waxing crescent Mercury, first quarter Mercury, waxing gibbous Mercury, full Mercury, waning gibbous Mercury, third quarter Mercury, and waning crescent Mercury.
Waxing gibbous Mercury in 2024
The waxing gibbous phase of Mercury will last from December 21 to February 8, 2025, when Mercury waxes or grows from half-Mercury to full Mercury. The waxing gibbous phase of Mercury will be visible in the eastern sky preceding sunrise as it rises before sunrise and sets before sunset.
The illuminated area of a waxing gibbous Mercury increases from 50% to 100% and its disk size decreases from 7 arcseconds to 5 arcseconds.
Full Mercury in 2025
The “full” phase of Mercury will fall on February 9, 2025. The “full” phase of Mercury will not be visible in the sky as it rises and sets with the sun.
A full Mercury is 100% illuminated and its disk size is 5 arcseconds.
Mercury is in its “full” phase when it passes the opposite side of the sun relative to Earth in its orbit. This is the superior conjunction position of Mercury. Mercury is farthest from our Earth (so smallest in size) during its “full” phase.
Waning gibbous Mercury in 2025
The waning gibbous phase of Mercury will last from February 10 to March 6, when Mercury wanes or shrinks from full Mercury to half-Mercury. The waning gibbous phase of Mercury will be visible in the western sky following sunset as it rises after sunrise and sets after sunset.
The illuminated area of a waning gibbous Mercury decreases from 100% to 50% and its disk size increases from 5 arcseconds to 7 arcseconds.
Third quarter Mercury in 2025
The third quarter phase of Mercury will fall on March 7, 2025. The third quarter phase of Mercury or half-Mercury will be visible in the western sky following sunset as it rises after sunrise and sets after sunset.
A third quarter Mercury is 50% illuminated and its disk size is 7 arcseconds.
Mercury is in its third quarter phase when it passes exactly three quarter area in its orbit from the inferior conjunction position. A third quarter Mercury, or half-Mercury, appears in the sky around the time of its greatest eastern elongation.
Waning crescent Mercury in 2025
The waning crescent phase of Mercury will last from March 8 to March 23, when Mercury wanes or shrinks from half-Mercury to new Mercury. The waning crescent phase of Mercury will be visible in the western sky following sunset as it rises after sunrise and sets after sunset.
The illuminated area of a waning crescent Mercury decreases from 50% to 0% and its disk size increases from 7 arcseconds to 11 arcseconds.
New Mercury in 2025
The “new” phase of Mercury will fall on March 24, 2025. The “new” phase of Mercury will not be visible in the sky as it rises and sets with the sun.
A new Mercury is 0% illuminated and its disk size is 11 arcseconds.
Mercury is in its “new” phase when it passes between the sun and Earth in its orbit. This is the inferior conjunction position of Mercury. Mercury is closest to our Earth (so largest in size) during its “new” phase.
Waxing crescent Mercury in 2025
The waxing crescent phase of Mercury will last from March 25 to April 23, when Mercury waxes or grows from new Mercury to half-Mercury. The waxing crescent phase of Mercury will be visible in the eastern sky preceding sunrise as it rises before sunrise and sets before sunset.
The illuminated area of a waxing crescent Mercury increases from 0% to 50% and its disk size decreases from 11 arcseconds to 7 arcseconds.
First quarter Mercury in 2025
The first quarter phase of Mercury will fall on April 24, 2025. The first quarter phase of Mercury or half-Mercury will be visible in the eastern sky preceding sunrise as it rises before sunrise and sets before sunset.
A first quarter Mercury is 50% illuminated and its disk size is 7 arcseconds.
Mercury is in its first quarter phase when it passes exactly one quarter area in its orbit from the inferior conjunction position. A first quarter Mercury, or half-Mercury, appears in the sky around the time of its greatest western elongation.
Why does Mercury have phases?
Mercury exhibits the full range of phases because the orbit of Mercury is smaller than the orbit of Earth.
When Mercury is located between the sun and Earth in its orbit, then the side of Mercury that faces us gets no light from the sun and exhibits its “new Mercury” phase.
When Mercury is located on the opposite side of the sun relative to Earth in its orbit, then the side of Mercury that faces us is fully illuminated and exhibits its “full Mercury” phase.
Difference between the moon phases and Mercury phases
The moon exhibits the same disk size throughout its phases as it orbits around Earth. However, Mercury doesn’t exhibit the same disk size throughout its phases from Earth as it orbits around the sun.
References
Geocentric Ephemeris for Mercury : 2024
Geocentric Ephemeris for Mercury : 2025
Please bookmark Spaceandtelescope.com or follow us on Facebook and Twitter to get latest space news, upcoming skywatching events and astronomy-related content.
