Sommers-Bausch Observatory - University of Colorado



Twilight Times - Year 2015 - Boulder, Colorado


All data and text courtesy the

US Naval Observatory Astronomical Applications




Civil Twilight

Civil twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 6 degrees below the horizon. This is the limit at which twilight illumination is sufficient, under good weather conditions, for terrestrial objects to be clearly distinguished; at the beginning of morning civil twilight, or end of evening civil twilight, the horizon is clearly defined and the brightest stars are visible under good atmospheric conditions in the absence of moonlight or other illumination. In the morning before the beginning of civil twilight and in the evening after the end of civil twilight, artificial illumination is normally required to carry on ordinary outdoor activities. Complete darkness, however, ends sometime prior to the beginning of morning civil twilight and begins sometime after the end of evening civil twilight.

             o  ,    o  ,                                  BOULDER, COLORADO                           Astronomical Applications Dept.
Location: W105 16, N40 01                               Civil Twilight for 2015                        U. S. Naval Observatory        
                                                                                                       Washington, DC  20392-5420     
                                                        Mountain Standard Time                                                        
                                                                                                                                      
                                                                                                                                      
       Jan.       Feb.       Mar.       Apr.       May        June       July       Aug.       Sept.      Oct.       Nov.       Dec.  
Day Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End
     h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m
01  0653 1717  0641 1749  0607 1820  0518 1853  0432 1925  0402 1956  0403 2006  0429 1945  0501 1901  0530 1811  0602 1727  0633 1706
02  0653 1718  0640 1750  0606 1821  0516 1854  0431 1926  0402 1957  0404 2006  0430 1944  0502 1859  0531 1809  0603 1726  0634 1706
03  0653 1718  0639 1751  0605 1822  0515 1855  0429 1927  0401 1957  0404 2006  0431 1943  0503 1857  0532 1807  0604 1725  0635 1706
04  0653 1719  0638 1752  0603 1823  0513 1856  0428 1928  0401 1958  0405 2006  0432 1942  0504 1856  0533 1806  0605 1724  0636 1706
05  0653 1720  0637 1753  0602 1824  0511 1857  0427 1929  0401 1959  0405 2006  0433 1940  0505 1854  0534 1804  0606 1723  0637 1706
06  0653 1721  0636 1754  0600 1825  0510 1858  0426 1930  0400 2000  0406 2005  0434 1939  0506 1852  0535 1803  0607 1722  0638 1706
07  0653 1722  0635 1755  0558 1826  0508 1859  0424 1932  0400 2000  0407 2005  0435 1938  0507 1851  0536 1801  0608 1721  0639 1706
08  0653 1723  0634 1757  0557 1827  0507 1900  0423 1933  0400 2001  0407 2004  0436 1937  0508 1849  0537 1800  0609 1720  0640 1706
09  0653 1724  0633 1758  0555 1828  0505 1901  0422 1934  0359 2001  0408 2004  0437 1935  0509 1847  0538 1758  0610 1719  0641 1706
10  0653 1725  0632 1759  0554 1829  0503 1902  0421 1935  0359 2002  0409 2004  0438 1934  0510 1846  0539 1756  0612 1718  0641 1706
11  0652 1726  0631 1800  0552 1831  0502 1903  0420 1936  0359 2003  0410 2003  0439 1933  0511 1844  0540 1755  0613 1717  0642 1706
12  0652 1727  0630 1801  0551 1832  0500 1904  0418 1937  0359 2003  0410 2003  0440 1931  0512 1842  0541 1753  0614 1716  0643 1706
13  0652 1728  0629 1802  0549 1833  0459 1905  0417 1938  0359 2004  0411 2002  0441 1930  0513 1841  0542 1752  0615 1715  0644 1707
14  0652 1729  0628 1803  0547 1834  0457 1906  0416 1939  0359 2004  0412 2001  0442 1928  0514 1839  0543 1750  0616 1715  0644 1707
15  0651 1730  0626 1804  0546 1835  0455 1907  0415 1940  0359 2004  0413 2001  0443 1927  0515 1837  0544 1749  0617 1714  0645 1707
16  0651 1731  0625 1806  0544 1836  0454 1909  0414 1941  0359 2005  0414 2000  0444 1925  0516 1835  0545 1748  0618 1713  0646 1707
17  0651 1732  0624 1807  0543 1837  0452 1910  0413 1942  0359 2005  0415 1959  0446 1924  0517 1834  0546 1746  0619 1712  0646 1708
18  0650 1733  0623 1808  0541 1838  0451 1911  0412 1943  0359 2005  0415 1959  0447 1922  0518 1832  0547 1745  0620 1712  0647 1708
19  0650 1734  0621 1809  0539 1839  0449 1912  0411 1944  0359 2006  0416 1958  0448 1921  0518 1830  0548 1743  0621 1711  0648 1709
20  0649 1735  0620 1810  0538 1840  0448 1913  0411 1945  0359 2006  0417 1957  0449 1919  0519 1829  0549 1742  0622 1711  0648 1709
21  0649 1736  0619 1811  0536 1841  0446 1914  0410 1946  0359 2006  0418 1956  0450 1918  0520 1827  0550 1741  0623 1710  0649 1710
22  0648 1737  0617 1812  0535 1842  0445 1915  0409 1947  0400 2006  0419 1955  0451 1916  0521 1825  0551 1739  0624 1710  0649 1710
23  0648 1738  0616 1813  0533 1843  0443 1916  0408 1948  0400 2007  0420 1954  0452 1915  0522 1824  0552 1738  0626 1709  0650 1711
24  0647 1740  0615 1814  0531 1844  0442 1917  0407 1949  0400 2007  0421 1954  0453 1913  0523 1822  0553 1737  0627 1709  0650 1711
25  0646 1741  0613 1816  0530 1845  0440 1918  0407 1950  0401 2007  0422 1953  0454 1912  0524 1820  0554 1735  0628 1708  0651 1712
26  0646 1742  0612 1817  0528 1846  0439 1920  0406 1951  0401 2007  0423 1952  0455 1910  0525 1819  0555 1734  0629 1708  0651 1712
27  0645 1743  0610 1818  0526 1847  0438 1921  0405 1952  0401 2007  0424 1951  0456 1909  0526 1817  0557 1733  0630 1707  0651 1713
28  0644 1744  0609 1819  0525 1848  0436 1922  0404 1953  0402 2007  0425 1950  0457 1907  0527 1815  0558 1732  0631 1707  0652 1714
29  0644 1745             0523 1849  0435 1923  0404 1954  0402 2007  0426 1949  0458 1905  0528 1814  0559 1730  0632 1707  0652 1714
30  0643 1746             0521 1850  0433 1924  0403 1954  0403 2007  0427 1947  0459 1904  0529 1812  0600 1729  0633 1707  0652 1715
31  0642 1748             0520 1851             0403 1955             0428 1946  0500 1902             0601 1728             0652 1716

                                             Add one hour for daylight time, if and when in use.




Nautical Twilight

Nautical twilight is defined to begin in the morning, and to end in the evening, when the center of the sun is geometrically 12 degrees below the horizon. At the beginning or end of nautical twilight, under good atmospheric conditions and in the absence of other illumination, general outlines of ground objects may be distinguishable, but detailed outdoor operations are not possible, and the horizon is indistinct.

             o  ,    o  ,                                  BOULDER, COLORADO                           Astronomical Applications Dept.
Location: W105 16, N40 01                             Nautical Twilight for 2015                       U. S. Naval Observatory        
                                                                                                       Washington, DC  20392-5420     
                                                        Mountain Standard Time                                                        
                                                                                                                                      
                                                                                                                                      
       Jan.       Feb.       Mar.       Apr.       May        June       July       Aug.       Sept.      Oct.       Nov.       Dec.  
Day Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End
     h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m
01  0619 1751  0609 1821  0536 1851  0446 1925  0356 2001  0322 2036  0322 2048  0352 2022  0428 1934  0459 1842  0530 1759  0600 1740
02  0619 1752  0608 1822  0535 1852  0444 1926  0355 2002  0321 2037  0322 2048  0353 2021  0429 1932  0500 1840  0531 1758  0601 1740
03  0619 1752  0607 1823  0533 1853  0442 1927  0353 2003  0321 2038  0323 2047  0354 2020  0430 1930  0501 1839  0532 1757  0602 1740
04  0619 1753  0606 1824  0532 1855  0441 1928  0352 2005  0320 2039  0324 2047  0355 2018  0431 1928  0502 1837  0533 1756  0603 1740
05  0619 1754  0605 1825  0530 1856  0439 1929  0351 2006  0320 2040  0324 2047  0356 2017  0432 1927  0503 1836  0534 1755  0603 1740
06  0619 1755  0604 1826  0529 1857  0437 1931  0349 2007  0319 2041  0325 2046  0357 2015  0433 1925  0504 1834  0535 1754  0604 1740
07  0619 1756  0603 1828  0527 1858  0436 1932  0348 2008  0319 2041  0326 2046  0359 2014  0434 1923  0505 1832  0536 1753  0605 1740
08  0619 1757  0602 1829  0526 1859  0434 1933  0346 2010  0318 2042  0327 2045  0400 2013  0435 1921  0506 1831  0537 1752  0606 1740
09  0619 1758  0601 1830  0524 1900  0432 1934  0345 2011  0318 2043  0327 2045  0401 2011  0436 1920  0507 1829  0538 1751  0607 1740
10  0619 1758  0600 1831  0522 1901  0430 1935  0344 2012  0318 2043  0328 2044  0402 2010  0437 1918  0508 1828  0539 1750  0607 1740
11  0619 1759  0559 1832  0521 1902  0429 1936  0342 2013  0318 2044  0329 2043  0403 2008  0438 1916  0509 1826  0540 1750  0608 1740
12  0619 1800  0558 1833  0519 1903  0427 1938  0341 2014  0317 2045  0330 2043  0405 2007  0439 1914  0510 1825  0541 1749  0609 1740
13  0618 1801  0557 1834  0518 1904  0425 1939  0340 2016  0317 2045  0331 2042  0406 2005  0441 1913  0511 1823  0542 1748  0610 1741
14  0618 1802  0556 1835  0516 1905  0424 1940  0339 2017  0317 2046  0332 2041  0407 2004  0442 1911  0512 1822  0543 1747  0610 1741
15  0618 1803  0555 1836  0514 1906  0422 1941  0337 2018  0317 2046  0333 2041  0408 2002  0443 1909  0513 1820  0544 1747  0611 1741
16  0618 1804  0553 1837  0513 1907  0420 1942  0336 2019  0317 2047  0334 2040  0409 2000  0444 1907  0514 1819  0545 1746  0612 1742
17  0617 1805  0552 1838  0511 1908  0419 1944  0335 2020  0317 2047  0335 2039  0411 1959  0445 1906  0515 1818  0546 1745  0612 1742
18  0617 1806  0551 1840  0510 1909  0417 1945  0334 2022  0317 2047  0336 2038  0412 1957  0446 1904  0516 1816  0547 1745  0613 1742
19  0617 1807  0550 1841  0508 1911  0415 1946  0333 2023  0317 2048  0337 2037  0413 1956  0447 1902  0517 1815  0548 1744  0613 1743
20  0616 1808  0548 1842  0506 1912  0414 1947  0332 2024  0317 2048  0338 2036  0414 1954  0448 1900  0518 1813  0549 1744  0614 1743
21  0616 1809  0547 1843  0505 1913  0412 1948  0331 2025  0318 2048  0339 2035  0415 1952  0449 1859  0519 1812  0550 1743  0615 1744
22  0615 1810  0546 1844  0503 1914  0410 1950  0330 2026  0318 2048  0340 2034  0416 1951  0450 1857  0520 1811  0551 1743  0615 1744
23  0615 1811  0545 1845  0501 1915  0409 1951  0329 2027  0318 2048  0341 2033  0418 1949  0451 1855  0521 1809  0552 1742  0616 1745
24  0614 1812  0543 1846  0459 1916  0407 1952  0328 2028  0318 2048  0342 2032  0419 1947  0452 1854  0522 1808  0553 1742  0616 1745
25  0614 1814  0542 1847  0458 1917  0406 1953  0327 2030  0319 2049  0343 2031  0420 1946  0453 1852  0523 1807  0554 1741  0616 1746
26  0613 1815  0540 1848  0456 1918  0404 1955  0326 2031  0319 2049  0345 2030  0421 1944  0454 1850  0524 1806  0555 1741  0617 1746
27  0612 1816  0539 1849  0454 1919  0402 1956  0325 2032  0320 2048  0346 2029  0422 1942  0455 1849  0525 1805  0556 1741  0617 1747
28  0612 1817  0538 1850  0453 1920  0401 1957  0325 2033  0320 2048  0347 2027  0423 1940  0456 1847  0526 1803  0557 1741  0617 1748
29  0611 1818             0451 1922  0359 1958  0324 2034  0321 2048  0348 2026  0424 1939  0457 1845  0527 1802  0558 1740  0618 1748
30  0610 1819             0449 1923  0358 2000  0323 2035  0321 2048  0349 2025  0425 1937  0458 1844  0528 1801  0559 1740  0618 1749
31  0609 1820             0448 1924             0322 2036             0350 2024  0427 1935             0529 1800             0618 1750

                                             Add one hour for daylight time, if and when in use.




Astronomical Twilight

Astronomical twilight is defined to begin in the morning, and to end in the evening when the center of the Sun is geometrically 18 degrees below the horizon. Before the beginning of astronomical twilight in the morning and after the end of astronomical twilight in the evening the Sun does not contribute to sky illumination; for a considerable interval after the beginning of morning twilight and before the end of evening twilight, sky illumination is so faint that it is practically imperceptible.

             o  ,    o  ,                                  BOULDER, COLORADO                           Astronomical Applications Dept.
Location: W105 16, N40 01                           Astronomical Twilight for 2015                     U. S. Naval Observatory        
                                                                                                       Washington, DC  20392-5420     
                                                        Mountain Standard Time                                                        
                                                                                                                                      
                                                                                                                                      
       Jan.       Feb.       Mar.       Apr.       May        June       July       Aug.       Sept.      Oct.       Nov.       Dec.  
Day Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End  Begin End
     h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m   h m  h m
01  0546 1824  0537 1853  0505 1923  0413 1958  0318 2039  0236 2123  0234 2136  0310 2103  0353 2008  0427 1914  0458 1830  0527 1813
02  0546 1824  0536 1854  0503 1924  0411 1959  0316 2041  0235 2124  0234 2136  0312 2102  0354 2006  0428 1912  0459 1829  0528 1812
03  0546 1825  0535 1855  0502 1925  0409 2001  0315 2042  0234 2125  0235 2135  0313 2100  0356 2004  0429 1910  0500 1828  0529 1812
04  0546 1826  0534 1856  0500 1926  0407 2002  0313 2044  0233 2126  0236 2135  0315 2058  0357 2002  0430 1909  0501 1827  0530 1812
05  0546 1827  0534 1857  0459 1927  0405 2003  0311 2045  0233 2127  0237 2134  0316 2057  0358 2000  0431 1907  0502 1826  0531 1812
06  0546 1828  0533 1858  0457 1928  0403 2005  0310 2047  0232 2128  0238 2133  0318 2055  0359 1959  0432 1905  0503 1826  0531 1812
07  0546 1828  0532 1859  0456 1929  0402 2006  0308 2048  0231 2129  0239 2133  0319 2053  0400 1957  0433 1904  0504 1825  0532 1813
08  0546 1829  0531 1900  0454 1930  0400 2007  0306 2050  0231 2130  0240 2132  0320 2052  0402 1955  0434 1902  0505 1824  0533 1813
09  0546 1830  0530 1901  0453 1931  0358 2008  0305 2051  0230 2131  0241 2131  0322 2050  0403 1953  0435 1901  0506 1823  0534 1813
10  0546 1831  0529 1902  0451 1933  0356 2010  0303 2053  0230 2131  0242 2130  0323 2048  0404 1951  0436 1859  0507 1822  0535 1813
11  0546 1832  0528 1903  0449 1934  0354 2011  0302 2054  0230 2132  0243 2130  0325 2047  0405 1949  0437 1858  0508 1821  0535 1813
12  0546 1833  0527 1904  0448 1935  0352 2012  0300 2056  0229 2133  0244 2129  0326 2045  0406 1947  0438 1856  0509 1821  0536 1813
13  0546 1834  0525 1906  0446 1936  0351 2014  0259 2057  0229 2134  0245 2128  0328 2043  0407 1946  0439 1855  0510 1820  0537 1814
14  0546 1835  0524 1907  0444 1937  0349 2015  0257 2059  0229 2134  0246 2127  0329 2041  0409 1944  0440 1853  0511 1819  0537 1814
15  0546 1836  0523 1908  0443 1938  0347 2016  0256 2100  0229 2135  0247 2126  0330 2039  0410 1942  0441 1852  0512 1819  0538 1814
16  0545 1837  0522 1909  0441 1939  0345 2018  0254 2102  0229 2135  0249 2125  0332 2038  0411 1940  0442 1850  0513 1818  0539 1815
17  0545 1838  0521 1910  0439 1940  0343 2019  0253 2103  0228 2136  0250 2124  0333 2036  0412 1938  0443 1849  0514 1817  0539 1815
18  0545 1839  0520 1911  0438 1942  0341 2021  0251 2105  0228 2136  0251 2123  0335 2034  0413 1936  0444 1847  0515 1817  0540 1815
19  0544 1840  0518 1912  0436 1943  0339 2022  0250 2106  0229 2136  0252 2121  0336 2032  0414 1935  0445 1846  0516 1816  0541 1816
20  0544 1841  0517 1913  0434 1944  0338 2023  0249 2107  0229 2137  0254 2120  0337 2030  0415 1933  0446 1845  0517 1816  0541 1816
21  0544 1842  0516 1914  0432 1945  0336 2025  0247 2109  0229 2137  0255 2119  0339 2029  0416 1931  0447 1843  0518 1815  0542 1817
22  0543 1843  0515 1915  0431 1946  0334 2026  0246 2110  0229 2137  0256 2118  0340 2027  0417 1929  0448 1842  0519 1815  0542 1817
23  0543 1844  0513 1916  0429 1947  0332 2028  0245 2112  0229 2137  0258 2116  0341 2025  0419 1927  0449 1841  0520 1815  0543 1818
24  0542 1845  0512 1917  0427 1949  0330 2029  0244 2113  0230 2137  0259 2115  0343 2023  0420 1926  0450 1840  0521 1814  0543 1818
25  0542 1846  0510 1918  0425 1950  0329 2031  0243 2114  0230 2137  0301 2114  0344 2021  0421 1924  0451 1838  0522 1814  0543 1819
26  0541 1847  0509 1919  0423 1951  0327 2032  0242 2116  0231 2137  0302 2112  0345 2019  0422 1922  0452 1837  0523 1814  0544 1819
27  0540 1848  0508 1921  0422 1952  0325 2034  0240 2117  0231 2137  0303 2111  0347 2017  0423 1920  0453 1836  0524 1813  0544 1820
28  0540 1849  0506 1922  0420 1953  0323 2035  0239 2118  0232 2137  0305 2109  0348 2015  0424 1919  0454 1835  0525 1813  0545 1821
29  0539 1850             0418 1955  0321 2036  0238 2119  0232 2137  0306 2108  0349 2014  0425 1917  0455 1834  0525 1813  0545 1821
30  0538 1851             0416 1956  0320 2038  0237 2121  0233 2136  0308 2106  0351 2012  0426 1915  0456 1833  0526 1813  0545 1822
31  0538 1852             0414 1957             0237 2122             0309 2105  0352 2010             0457 1831             0545 1823

                                             Add one hour for daylight time, if and when in use.