- published: 02 Sep 2008
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A day is a unit of time. In common usage, it is an interval equal to 24 hours. It also can mean the consecutive period of time during which the Sun is above the horizon, also known as daytime. The period of time during which the Earth completes one rotation with respect to the Sun is called a solar day.
Several definitions of this universal human concept are used according to context, need and convenience. In 1967, the second was redefined in terms of the wavelength of light, and was designated the SI base unit of time. The unit of measurement "day", redefined in 1967 as 86 400 SI seconds and symbolized d, is not an SI unit, but is accepted for use with SI. A civil day is usually also 86 400 seconds, plus or minus a possible leap second in Coordinated Universal Time (UTC), and, in some locations, occasionally plus or minus an hour when changing from or to daylight saving time. The word day may also refer to a day of the week or to a calendar date, as in answer to the question "On which day?" The life patterns of humans and many other species are related to Earth's solar day and the day-night cycle (see circadian rhythms).
Michelle LaVaughn Robinson Obama (born January 17, 1964) is an American lawyer and writer. She is married to the 44th and current President of the United States, Barack Obama, and is the first African-American First Lady of the United States. Raised on the South Side of Chicago, she is a graduate of Princeton University and Harvard Law School, and spent the early part of her legal career working at the law firm Sidley Austin, where she met Barack. Subsequently, she worked as part of the staff of Chicago mayor Richard M. Daley, and for the University of Chicago Medical Center.
Throughout 2007 and 2008, Obama helped campaign for her husband's presidential bid. She delivered a keynote address at the 2008 Democratic National Convention and spoke at the 2012 Democratic National Convention. She and her husband have two daughters together. She has become a fashion icon and role model for women, and an advocate for poverty awareness, nutrition, physical activity, and healthy eating.