Day-of-Year Numbering System

How AZMET denotes Days and Hours

AZMET raw data files use the Day-of-Year (DOY) numbering system. This is a common format used in research data and by the military. The Day-of-Year system ignores the existance of months and numbers each day of the year consecutively.
During normal years we number each day of the year from 1 to 365 During leap years we insert the 'leap day' (Feb 29), at Day-of-Year 60, thus shifting the rest of the year 'down' by one day. The Day-of-Year system is used in both the Daily and Hourly data files.

Note:
There are some other weather data collection agencies which use different calendar formats for their data. They set the length of all years to a 366 days. Their 'leap day' (Feb 29; DOY 60) is left blank (zeros or null data values) for non-leap years. During leap years the leap day position does contain data. AZMET does not use this method. Our years vary in length.

AZMET uses a 24 hour clock.
We number each hour of the day from 1 to 24.
Obviously, this is used in the Hourly data files.
[We do not use the 'digital clock' with colon format (ie 1:00 to 24:00).
Nor do we use the 100 to 2400 format.]

All AZMET data are collected, stored and presented in
local 'Arizona' time, which is in the 'Mountain Standard' time zone.
Arizona does not participate in Daylight Savings Time.
Therefore, the times listed in the AZMET data files are
always seven hours 'behind' Coordinated Universal Time (UTC)
(aka: Greenwich Mean time; Zulu time).
More information on 'Universal Time'
Converting 'Universal Time' to US Time Zones

Below are several tables and lists, to aid you in visualizing the Day-of-Year system : In this first table, the Day-of-Year numbers are grouped by month : Day-of-Year by Month ======================================= Normal Year Leap Year -------------- --------------- Jan 1 - 31 Jan 1 - 31 Feb 32 - 59 Feb 32 - 60 Mar 60 - 90 Mar 61 - 91 Apr 91 - 120 Apr 92 - 121 May 121 - 151 May 122 - 152 Jun 152 - 181 Jun 153 - 182 Jul 182 - 212 Jul 183 - 213 Aug 213 - 243 Aug 214 - 244 Sep 244 - 273 Sep 245 - 274 Oct 274 - 304 Oct 275 - 305 Nov 305 - 334 Nov 306 - 335 Dec 335 - 365 Dec 336 - 366

In this second calendar table, The upper number in each box represents the normal calendar day of the month. The lower number in each box represents the Day-of-Year (DOY).

January +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 1| 2| 3| 4| 5| 6| 7| 8| 9| 10| 11| 12| 13| 14| 15| 16| 17| 18| 19| | 1| 2| 3| 4| 5| 6| 7| 8| 9| 10| 11| 12| 13| 14| 15| 16| 17| 18| 19| +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 20| 21| 22| 23| 24| 25| 26| 27| 28| 29| 30| 31| | | 20| 21| 22| 23| 24| 25| 26| 27| 28| 29| 30| 31| | +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ February +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 1| 2| 3| 4| 5| 6| 7| 8| 9| 10| 11| 12| 13| 14| 15| 16| 17| 18| 19| | 32| 33| 34| 35| 36| 37| 38| 39| 40| 41| 42| 43| 44| 45| 46| 47| 48| 49| 50| +---+---+---+---+---+---+---+---+---+******-+---+---+---+---+---+---+---+---+ | 20| 21| 22| 23| 24| 25| 26| 27| 28 * 29 * NOTE: During leap years, add 1 | | 51| 52| 53| 54| 55| 56| 57| 58| 59 * 60 * to each Day-of-Year after FEB 29| +---+---+---+---+---+---+---+---+---+******-+---+---+---+---+---+---+---+---+ March +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 1| 2| 3| 4| 5| 6| 7| 8| 9| 10| 11| 12| 13| 14| 15| 16| 17| 18| 19| | 60| 61| 62| 63| 64| 65| 66| 67| 68| 69| 70| 71| 72| 73| 74| 75| 76| 77| 78| +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 20| 21| 22| 23| 24| 25| 26| 27| 28| 29| 30| 31| Add 1 to DOY | | 79| 80| 81| 82| 83| 84| 85| 86| 87| 88| 89| 90| during leap years. | +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ April +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 1| 2| 3| 4| 5| 6| 7| 8| 9| 10| 11| 12| 13| 14| 15| 16| 17| 18| 19| | 91| 92| 93| 94| 95| 96| 97| 98| 99|100|101|102|103|104|105|106|107|108|109| +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 20| 21| 22| 23| 24| 25| 26| 27| 28| 29| 30| Add 1 to DOY | |110|111|112|113|114|115|116|117|118|119|120| during leap years. | +---+---+---+---+---+---+---+---+---+---+---+-------------------------------+ May +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 1| 2| 3| 4| 5| 6| 7| 8| 9| 10| 11| 12| 13| 14| 15| 16| 17| 18| 19| |121|122|123|124|125|126|127|128|129|130|131|132|133|134|135|136|137|138|139| +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 20| 21| 22| 23| 24| 25| 26| 27| 28| 29| 30| 31| Add 1 to DOY | |140|141|142|143|144|145|146|147|148|149|150|151| during leap years. | +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ June +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 1| 2| 3| 4| 5| 6| 7| 8| 9| 10| 11| 12| 13| 14| 15| 16| 17| 18| 19| |152|153|154|155|156|157|158|159|160|161|162|163|164|165|166|167|168|169|170| +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 20| 21| 22| 23| 24| 25| 26| 27| 28| 29| 30| Add 1 to DOY | |171|172|173|174|175|176|177|178|179|180|181| during leap years. | +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ July +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 1| 2| 3| 4| 5| 6| 7| 8| 9| 10| 11| 12| 13| 14| 15| 16| 17| 18| 19| |182|183|184|185|186|187|188|189|190|191|192|193|194|195|196|197|198|199|200| +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 20| 21| 22| 23| 24| 25| 26| 27| 28| 29| 30| 31| Add 1 to DOY | |201|202|203|204|205|206|207|208|209|210|211|212| during leap years. | +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ August +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 1| 2| 3| 4| 5| 6| 7| 8| 9| 10| 11| 12| 13| 14| 15| 16| 17| 18| 19| |213|214|215|216|217|218|219|220|221|222|223|224|225|226|227|228|229|230|231| +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 20| 21| 22| 23| 24| 25| 26| 27| 28| 29| 30| 31| Add 1 to DOY | |232|233|234|235|236|237|238|239|240|241|242|243| during leap years. | +---+---+---+---+---+---+---+---+---+---+---+---+---------------------------+ September +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 1| 2| 3| 4| 5| 6| 7| 8| 9| 10| 11| 12| 13| 14| 15| 16| 17| 18| 19| |244|245|246|247|248|249|250|251|252|253|254|255|256|257|258|259|260|261|262| +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 20| 21| 22| 23| 24| 25| 26| 27| 28| 29| 30| Add 1 to DOY | |263|264|265|266|267|268|269|270|271|272|273| during leap years. | +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ October +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 1| 2| 3| 4| 5| 6| 7| 8| 9| 10| 11| 12| 13| 14| 15| 16| 17| 18| 19| |274|275|276|277|278|279|280|281|282|283|284|285|286|287|288|289|290|291|292| +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 20| 21| 22| 23| 24| 25| 26| 27| 28| 29| 30| 31| Add 1 to DOY | |293|294|295|296|297|298|299|300|301|302|303|304| during leap years. | +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ November +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 1| 2| 3| 4| 5| 6| 7| 8| 9| 10| 11| 12| 13| 14| 15| 16| 17| 18| 19| |305|306|307|308|309|310|311|312|313|314|315|316|317|318|319|320|321|322|323| +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 20| 21| 22| 23| 24| 25| 26| 27| 28| 29| 30| Add 1 to DOY | |324|325|326|327|328|329|330|331|332|333|334| during leap years. | +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ December +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 1| 2| 3| 4| 5| 6| 7| 8| 9| 10| 11| 12| 13| 14| 15| 16| 17| 18| 19| |335|336|337|338|339|340|341|342|343|344|345|346|347|348|349|350|351|352|353| +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 20| 21| 22| 23| 24| 25| 26| 27| 28| 29| 30| 31| Add 1 to DOY | |354|355|356|357|358|359|360|361|362|363|364|365| during leap years. | +---+---+---+---+---+---+---+---+---+---+---+---+---------------------------+ Julian Normal Leap Day Year Year ----- ------ ------ 1 = Jan 1 Jan 1 2 = Jan 2 Jan 2 3 = Jan 3 Jan 3 4 = Jan 4 Jan 4 5 = Jan 5 Jan 5 6 = Jan 6 Jan 6 7 = Jan 7 Jan 7 8 = Jan 8 Jan 8 9 = Jan 9 Jan 9 10 = Jan 10 Jan 10 11 = Jan 11 Jan 11 12 = Jan 12 Jan 12 13 = Jan 13 Jan 13 14 = Jan 14 Jan 14 15 = Jan 15 Jan 15 16 = Jan 16 Jan 16 17 = Jan 17 Jan 17 18 = Jan 18 Jan 18 19 = Jan 19 Jan 19 20 = Jan 20 Jan 20 21 = Jan 21 Jan 21 22 = Jan 22 Jan 22 23 = Jan 23 Jan 23 24 = Jan 24 Jan 24 25 = Jan 25 Jan 25 26 = Jan 26 Jan 26 27 = Jan 27 Jan 27 28 = Jan 28 Jan 28 29 = Jan 29 Jan 29 30 = Jan 30 Jan 30 31 = Jan 31 Jan 31 32 = Feb 1 Feb 1 33 = Feb 2 Feb 2 34 = Feb 3 Feb 3 35 = Feb 4 Feb 4 36 = Feb 5 Feb 5 37 = Feb 6 Feb 6 38 = Feb 7 Feb 7 39 = Feb 8 Feb 8 40 = Feb 9 Feb 9 41 = Feb 10 Feb 10 42 = Feb 11 Feb 11 43 = Feb 12 Feb 12 44 = Feb 13 Feb 13 45 = Feb 14 Feb 14 46 = Feb 15 Feb 15 47 = Feb 16 Feb 16 48 = Feb 17 Feb 17 49 = Feb 18 Feb 18 50 = Feb 19 Feb 19 51 = Feb 20 Feb 20 52 = Feb 21 Feb 21 53 = Feb 22 Feb 22 54 = Feb 23 Feb 23 55 = Feb 24 Feb 24 56 = Feb 25 Feb 25 57 = Feb 26 Feb 26 58 = Feb 27 Feb 27 59 = Feb 28 Feb 28 60 = Mar 1 Feb 29 61 = Mar 2 Mar 1 62 = Mar 3 Mar 2 63 = Mar 4 Mar 3 64 = Mar 5 Mar 4 65 = Mar 6 Mar 5 66 = Mar 7 Mar 6 67 = Mar 8 Mar 7 68 = Mar 9 Mar 8 69 = Mar 10 Mar 9 70 = Mar 11 Mar 10 71 = Mar 12 Mar 11 72 = Mar 13 Mar 12 73 = Mar 14 Mar 13 74 = Mar 15 Mar 14 75 = Mar 16 Mar 15 76 = Mar 17 Mar 16 77 = Mar 18 Mar 17 78 = Mar 19 Mar 18 79 = Mar 20 Mar 19 80 = Mar 21 Mar 20 81 = Mar 22 Mar 21 82 = Mar 23 Mar 22 83 = Mar 24 Mar 23 84 = Mar 25 Mar 24 85 = Mar 26 Mar 25 86 = Mar 27 Mar 26 87 = Mar 28 Mar 27 88 = Mar 29 Mar 28 89 = Mar 30 Mar 29 90 = Mar 31 Mar 30 91 = Apr 1 Mar 31 92 = Apr 2 Apr 1 93 = Apr 3 Apr 2 94 = Apr 4 Apr 3 95 = Apr 5 Apr 4 96 = Apr 6 Apr 5 97 = Apr 7 Apr 6 98 = Apr 8 Apr 7 99 = Apr 9 Apr 8 100 = Apr 10 Apr 9 101 = Apr 11 Apr 10 102 = Apr 12 Apr 11 103 = Apr 13 Apr 12 104 = Apr 14 Apr 13 105 = Apr 15 Apr 14 106 = Apr 16 Apr 15 107 = Apr 17 Apr 16 108 = Apr 18 Apr 17 109 = Apr 19 Apr 18 110 = Apr 20 Apr 19 111 = Apr 21 Apr 20 112 = Apr 22 Apr 21 113 = Apr 23 Apr 22 114 = Apr 24 Apr 23 115 = Apr 25 Apr 24 116 = Apr 26 Apr 25 117 = Apr 27 Apr 26 118 = Apr 28 Apr 27 119 = Apr 29 Apr 28 120 = Apr 30 Apr 29 121 = May 1 Apr 30 122 = May 2 May 1 123 = May 3 May 2 124 = May 4 May 3 125 = May 5 May 4 126 = May 6 May 5 127 = May 7 May 6 128 = May 8 May 7 129 = May 9 May 8 130 = May 10 May 9 131 = May 11 May 10 132 = May 12 May 11 133 = May 13 May 12 134 = May 14 May 13 135 = May 15 May 14 136 = May 16 May 15 137 = May 17 May 16 138 = May 18 May 17 139 = May 19 May 18 140 = May 20 May 19 141 = May 21 May 20 142 = May 22 May 21 143 = May 23 May 22 144 = May 24 May 23 145 = May 25 May 24 146 = May 26 May 25 147 = May 27 May 26 148 = May 28 May 27 149 = May 29 May 28 150 = May 30 May 29 151 = May 31 May 30 152 = Jun 1 May 31 153 = Jun 2 Jun 1 154 = Jun 3 Jun 2 155 = Jun 4 Jun 3 156 = Jun 5 Jun 4 157 = Jun 6 Jun 5 158 = Jun 7 Jun 6 159 = Jun 8 Jun 7 160 = Jun 9 Jun 8 161 = Jun 10 Jun 9 162 = Jun 11 Jun 10 163 = Jun 12 Jun 11 164 = Jun 13 Jun 12 165 = Jun 14 Jun 13 166 = Jun 15 Jun 14 167 = Jun 16 Jun 15 168 = Jun 17 Jun 16 169 = Jun 18 Jun 17 170 = Jun 19 Jun 18 171 = Jun 20 Jun 19 172 = Jun 21 Jun 20 173 = Jun 22 Jun 21 174 = Jun 23 Jun 22 175 = Jun 24 Jun 23 176 = Jun 25 Jun 24 177 = Jun 26 Jun 25 178 = Jun 27 Jun 26 179 = Jun 28 Jun 27 180 = Jun 29 Jun 28 181 = Jun 30 Jun 29 182 = Jul 1 Jun 30 183 = Jul 2 Jul 1 184 = Jul 3 Jul 2 185 = Jul 4 Jul 3 186 = Jul 5 Jul 4 187 = Jul 6 Jul 5 188 = Jul 7 Jul 6 189 = Jul 8 Jul 7 190 = Jul 9 Jul 8 191 = Jul 10 Jul 9 192 = Jul 11 Jul 10 193 = Jul 12 Jul 11 194 = Jul 13 Jul 12 195 = Jul 14 Jul 13 196 = Jul 15 Jul 14 197 = Jul 16 Jul 15 198 = Jul 17 Jul 16 199 = Jul 18 Jul 17 200 = Jul 19 Jul 18 201 = Jul 20 Jul 19 202 = Jul 21 Jul 20 203 = Jul 22 Jul 21 204 = Jul 23 Jul 22 205 = Jul 24 Jul 23 206 = Jul 25 Jul 24 207 = Jul 26 Jul 25 208 = Jul 27 Jul 26 209 = Jul 28 Jul 27 210 = Jul 29 Jul 28 211 = Jul 30 Jul 29 212 = Jul 31 Jul 30 213 = Aug 1 Jul 31 214 = Aug 2 Aug 1 215 = Aug 3 Aug 2 216 = Aug 4 Aug 3 217 = Aug 5 Aug 4 218 = Aug 6 Aug 5 219 = Aug 7 Aug 6 220 = Aug 8 Aug 7 221 = Aug 9 Aug 8 222 = Aug 10 Aug 9 223 = Aug 11 Aug 10 224 = Aug 12 Aug 11 225 = Aug 13 Aug 12 226 = Aug 14 Aug 13 227 = Aug 15 Aug 14 228 = Aug 16 Aug 15 229 = Aug 17 Aug 16 230 = Aug 18 Aug 17 231 = Aug 19 Aug 18 232 = Aug 20 Aug 19 233 = Aug 21 Aug 20 234 = Aug 22 Aug 21 235 = Aug 23 Aug 22 236 = Aug 24 Aug 23 237 = Aug 25 Aug 24 238 = Aug 26 Aug 25 239 = Aug 27 Aug 26 240 = Aug 28 Aug 27 241 = Aug 29 Aug 28 242 = Aug 30 Aug 29 243 = Aug 31 Aug 30 244 = Sep 1 Aug 31 245 = Sep 2 Sep 1 246 = Sep 3 Sep 2 247 = Sep 4 Sep 3 248 = Sep 5 Sep 4 249 = Sep 6 Sep 5 250 = Sep 7 Sep 6 251 = Sep 8 Sep 7 252 = Sep 9 Sep 8 253 = Sep 10 Sep 9 254 = Sep 11 Sep 10 255 = Sep 12 Sep 11 256 = Sep 13 Sep 12 257 = Sep 14 Sep 13 258 = Sep 15 Sep 14 259 = Sep 16 Sep 15 260 = Sep 17 Sep 16 261 = Sep 18 Sep 17 262 = Sep 19 Sep 18 263 = Sep 20 Sep 19 264 = Sep 21 Sep 20 265 = Sep 22 Sep 21 266 = Sep 23 Sep 22 267 = Sep 24 Sep 23 268 = Sep 25 Sep 24 269 = Sep 26 Sep 25 270 = Sep 27 Sep 26 271 = Sep 28 Sep 27 272 = Sep 29 Sep 28 273 = Sep 30 Sep 29 274 = Oct 1 Sep 30 275 = Oct 2 Oct 1 276 = Oct 3 Oct 2 277 = Oct 4 Oct 3 278 = Oct 5 Oct 4 279 = Oct 6 Oct 5 280 = Oct 7 Oct 6 281 = Oct 8 Oct 7 282 = Oct 9 Oct 8 283 = Oct 10 Oct 9 284 = Oct 11 Oct 10 285 = Oct 12 Oct 11 286 = Oct 13 Oct 12 287 = Oct 14 Oct 13 288 = Oct 15 Oct 14 289 = Oct 16 Oct 15 290 = Oct 17 Oct 16 291 = Oct 18 Oct 17 292 = Oct 19 Oct 18 293 = Oct 20 Oct 19 294 = Oct 21 Oct 20 295 = Oct 22 Oct 21 296 = Oct 23 Oct 22 297 = Oct 24 Oct 23 298 = Oct 25 Oct 24 299 = Oct 26 Oct 25 300 = Oct 27 Oct 26 301 = Oct 28 Oct 27 302 = Oct 29 Oct 28 303 = Oct 30 Oct 29 304 = Oct 31 Oct 30 305 = Nov 1 Oct 31 306 = Nov 2 Nov 1 307 = Nov 3 Nov 2 308 = Nov 4 Nov 3 309 = Nov 5 Nov 4 310 = Nov 6 Nov 5 311 = Nov 7 Nov 6 312 = Nov 8 Nov 7 313 = Nov 9 Nov 8 314 = Nov 10 Nov 9 315 = Nov 11 Nov 10 316 = Nov 12 Nov 11 317 = Nov 13 Nov 12 318 = Nov 14 Nov 13 319 = Nov 15 Nov 14 320 = Nov 16 Nov 15 321 = Nov 17 Nov 16 322 = Nov 18 Nov 17 323 = Nov 19 Nov 18 324 = Nov 20 Nov 19 325 = Nov 21 Nov 20 326 = Nov 22 Nov 21 327 = Nov 23 Nov 22 328 = Nov 24 Nov 23 329 = Nov 25 Nov 24 330 = Nov 26 Nov 25 331 = Nov 27 Nov 26 332 = Nov 28 Nov 27 333 = Nov 29 Nov 28 334 = Nov 30 Nov 29 335 = Dec 1 Nov 30 336 = Dec 2 Dec 1 337 = Dec 3 Dec 2 338 = Dec 4 Dec 3 339 = Dec 5 Dec 4 340 = Dec 6 Dec 5 341 = Dec 7 Dec 6 342 = Dec 8 Dec 7 343 = Dec 9 Dec 8 344 = Dec 10 Dec 9 345 = Dec 11 Dec 10 346 = Dec 12 Dec 11 347 = Dec 13 Dec 12 348 = Dec 14 Dec 13 349 = Dec 15 Dec 14 350 = Dec 16 Dec 15 351 = Dec 17 Dec 16 352 = Dec 18 Dec 17 353 = Dec 19 Dec 18 354 = Dec 20 Dec 19 355 = Dec 21 Dec 20 356 = Dec 22 Dec 21 357 = Dec 23 Dec 22 358 = Dec 24 Dec 23 359 = Dec 25 Dec 24 360 = Dec 26 Dec 25 361 = Dec 27 Dec 26 362 = Dec 28 Dec 27 363 = Dec 29 Dec 28 364 = Dec 30 Dec 29 365 = Dec 31 Dec 30 366 = Dec 31 Day-of-Year by Month ======================================= Normal Year Leap Year -------------- --------------- Jan 1 - 31 Jan 1 - 31 Feb 32 - 59 Feb 32 - 60 Mar 60 - 90 Mar 61 - 91 Apr 91 - 120 Apr 92 - 121 May 121 - 151 May 122 - 152 Jun 152 - 181 Jun 153 - 182 Jul 182 - 212 Jul 183 - 213 Aug 213 - 243 Aug 214 - 244 Sep 244 - 273 Sep 245 - 274 Oct 274 - 304 Oct 275 - 305 Nov 305 - 334 Nov 306 - 335 Dec 335 - 365 Dec 336 - 366 Recent Leap Years: Past and future Leap Years ============================ ================================== 1987 1896 1936 1972 2008 * 1988 - Leap Year 1904 1940 1976 2012 1989 1908 1944 1980 2016 1990 1912 1948 1984 2020 1991 1916 1952 1988 2024 * 1992 - Leap Year 1920 1956 1992 2028 1993 1924 1960 1996 2032 1994 1928 1964 2000 2036 1995 1932 1968 2004 2040 * 1996 - Leap Year 1997 1998 1999 * 2000 - Leap Year (Rule-of-Thumb : Leap Years = U.S. Presidential Election Years) Official Leap Year Rules : If a year is evenly divisible by 4 it is a leap year. Examples: 1996 / 4 = 499 therefore it is a leap year 1997 / 4 = 499.25 therefore it is not a leap year First Exception: Of those years which are evenly divisible by 4, if the year is also evenly divisible by 100, it is NOT a leap year. Example: 1900 / 4 = 475 1900 / 100 = 19 therefore it is NOT a leap year Second Exception: Of those years which are evenly divisible by 4 and 100, if the year is also evenly divisible by 400, it IS a leap year. Example: 2000 / 4 = 500 2000 / 100 = 20 2000 / 400 = 5 therefore it IS a leap year 1900 / 400 = 4.75 therefore it is NOT a leap year The Julian Calendar was developed by Julius Caesar and Egyptian astronomer Sosigenes in the year 46 BC. They sought to create a 12 month calendar which was based on a solar year; the time it takes for the earth to make one full orbit around the sun, which is 365.2422 days. (Prior to this, the Romans and most other civilizations used a lunar or lunar-solar hybrid calendar; only Egypt had a strictly solar calendar.) They set a normal year to equal 365 days, then designated every forth year (leap year) to have 366 days. This was to correct for the partial .2422 day which was missing from the current year and from each of the previous three years. To accomplish this they included the 'evenly divisible by 4' rule in their calendar. The Julian Calendar was adopted by the Council of Nicaea in 325 AD. However, by 1582 AD the number of past leap years had overcorrected (.2422 multiplied by 4 years = .9688 day, not 1 day) and the Julian Calendar had gained 10 days on earth's actual orbital position around the sun. If left unchecked, Easter would eventually occur in summer. To correct this, Pope Gregory XIII dropped 10 days from 1582 and enacted the first and second exceptions ('evenly divisible by 100 and by 400') as described above. The first exception excludes a leap year every 100 years. By using only the first exception, the calendar would, after several centuries, be slightly undercorrected. That is, it would have fallen behind earth's true orbital position. Realizing this, the Pope's mathematicians added the second exception which includes a leap year every 400 years (1600, 2000, 2400, etc). These rules do not fully correct the calendar to a perfect 365.2422 days per year; by the year 5000 AD it will have gained 1 day and another adjustment will be necessary. The 'calendar' section of any good Almanac will verify these rules regarding leap years ----- TIME: All AZMET data are collected, stored and presented in local 'Arizona' time, which is in the 'Mountain Standard' time zone. Arizona does not participate in Daylight Savings Time. Therefore, the times listed in the AZMET data files are always seven hours 'behind' Coordinated Universal Time (UTC) (aka: Greenwich Mean time; Zulu time).
More information on 'Universal Time'
Converting 'Universal Time' to US Time Zones

UTC Arizona Arizona 12hr ------ ------- ------------- 8:00 1:00 1:00 am 9:00 2:00 2:00 am 10:00 3:00 3:00 am 11:00 4:00 4:00 am 12:00 5:00 5:00 am 13:00 6:00 6:00 am 14:00 7:00 7:00 am 15:00 8:00 8:00 am 16:00 9:00 9:00 am 17:00 10:00 10:00 am 18:00 11:00 11:00 am 19:00 12:00 12:00 am 20:00 13:00 1:00 pm 21:00 14:00 2:00 pm 22:00 15:00 3:00 pm 23:00 16:00 4:00 pm 24:00 17:00 5:00 pm 1:00 18:00 6:00 pm 2:00 19:00 7:00 pm 3:00 20:00 8:00 pm 4:00 21:00 9:00 pm 5:00 22:00 10:00 pm 6:00 23:00 11:00 pm 7:00 24:00 12:00 pm