The National Academy of Sciences (NAS) is a United States nonprofit, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the National Academy of Medicine (NAM).

As a national academy, new members of the organization are elected annually by current members, based on their distinguished and continuing achievements in original research. Election to the National Academy is one of the highest honors in the scientific field. Members of the National Academy of Sciences serve pro bono as "advisers to the nation" on science, engineering, and medicine. The group holds a congressional charter under Title 36 of the United States Code.

Founded in 1863 as a result of an Act of Congress that was approved by Abraham Lincoln, the NAS is charged with "providing independent, objective advice to the nation on matters related to science and technology. … to provide scientific advice to the government 'whenever called upon' by any government department."[2]

The Academy receives no compensation from the government for its services.[3]

The Academy currently has 2,984 members and international members. Existing members elect new members for life. Up to 120 members are elected every year; up to 30 foreign citizens may be elected as international members annually. The election process begins with a formal nomination, followed by a vetting period, and culminates in a final ballot at the Academy's annual meeting in April each year. Members are affiliated with a section -- a specific scientific field -- in one of six so-called "classes": (1) Physical and Mathematical Sciences; (2) Biological Sciences; (3) Engineering and Applied Sciences; (4) Biomedical Sciences; (5) Behavioral and Social Sciences; and (6) Applied Biological, Agricultural, and Environmental Sciences.[6] Since its founding, the Academy has elected 6,457 members. Harvard University is associated with the most members (329), some 5% of the all-time total. The top ten institutions, half of which are Ivy League universities, account for nearly 28% of all members ever elected.[11]

Federal-style homes became popular after the American Revolution and were a refined upgrade to the popular Georgian house style. They have the same recurring shape and symmetry as other Colonial house styles, but their delicate ornamentation sets them apart.

Federal Colonial homes often feature:

• A layout built around a central hall
• An elliptical fanlight and two flanking lights (windows) around the door
• Paladin or tripartite windows

The elliptical fanlights and paladin windows are key distinguishing features from Georgian-style homes.

Contemporary homes resemble the modern homes of the mid-20th century with a renewed emphasis on sustainability. Current contemporary styles are rooted in minimalism, which you can see in these key features:

• Asymmetrical exterior
• Clean lines
• Open floor plan layout
• Geometry highlighted in its structure
• Sustainable building materials and features

Contemporary homes aim to find beauty in a simple and appealing design with ties to nature and more warmth than modern home styles offer.

The American Farmhouse is a simple and timeless style. Farmhouses are designed to be practical first and foremost. They’re common across the US and often showcase regional variations, like wrap-around porches in the South.

Farmhouses have evolved with time and location, but often feature these elements:

• Rectangular floor plan
• Large front porches
• Natural wood and stone materials
• Few and small windows
• Formal front rooms separated from family rooms

Of course, the easiest way to identify a farmhouse is that they’ll often be situated on a large plot of farmland.

Around the 1820s, Americans experienced a renewed interest in classic Greek and Roman culture. This cultural shift was a natural fit for architects, who brought the Greek Revival house style to life.

Greek Revival architecture became popular in homes as well as businesses, banks, and churches. Prominent features include:

• Easy to identify shapes, including a rectangular building and triangular roofs
• Gable-front designs
• Large porches and protected entryways
• Greek-inspired columns both square and round

Greek Revival homes often have decorative trim and moulding around the front door and windows. These ornate features and columns are easy ways to identify Greek Revival architecture.

Ranch house styles are the most searched style in the US today and are common in cities and suburbs across the country. There are various ranch house styles, including California and split-level ranch homes. The main distinguishing features between these styles are living space and home layout.

Ranch style homes feature:

• Single-story floor plans with low-pitched roofs
• Rectangular, “U,” or “L” shaped open floor plans
• Patio or deck space connected to the home
• Often includes a finished basement or attached garage

Ranch homes are the most popular homes in 34 US states — particularly in the Midwest and on the East Coast.

Mediterranean home styles are made of stucco, so they’re most common in warm climate states like Arizona and California. These homes grew in popularity in the 1920s and ‘30s after being featured as homes for the rich and famous on the silver screen.

Mediterranean-style homes include Spanish and Italian architectural elements. These key features make them easy to spot:

• Stucco walls painted white or brown
• Classic red tile roofs
• Arched doorways and windows
• Ornamentation including wrought iron, heavy doors, and decorative tiles

Mediterranean homes still carry the feelings of class and luxury they were built with over 100 years ago, with an added element of history and charm.