I had a question posed to me the other day around daylight savings time and how we figure it in chart construction. Since most Astrologers address this at the point of chart construction, and in the configuration of software programs that construct charts, this is a topic that is discussed in detail rarely.
First of all when we construct a chart for a person (natal, relational, progression, transit), and it is a local area event we may know whether daylight savings time is in effect. An ephemeris can also help us to sort out the time zones and exact corrections we need to make to a chart based on the time of birth. That being said, not all regions observe daylight savings time, and those that do often vary on the dates that daylight savings time is in effect. Because of this it can seem daunting trying to make correct calculations to a chart.
But why do we care if we are off by an hour? Well when constructing a chart for any purpose knowing the birth, or event time, to the closest and most accurate allows our interpretations to be exacting. Since the Ascendant moves one degree every four minutes, and since minutes in a chart can change the house placement and distribution of planets, and also effect the relational aspects the planets have with one another and with key points in the chart it is crucial that we be as accurate as possible.
While it is true in adjusting our clocks we spring forward in time in the Spring and fall back in time in the Fall, the only real adjustment we care about is the forward change in the Spring. But why? Well, the Fall time setting is the time setting before an adjustment has been made. It is the original time setting. The only alteration to time comes in the Spring when we move forward an hour from the regular time setting. In the Fall we simply return to to the original time setting. So even though we are moving the clocks back we would not need to adjust the time or time zone to reflect a change, but rather return to the original time zone and standard time.
For example, if someone was born in the month of May in Denver which is naturally time zone 7, but since they are born in May which is during daylight savings time we would choose MDT for Mountain Daylight Time, and it changes the time zone to 6 to make the correction. But let's say this same person was born in November instead. In this case we would leave the time zone alone as time zone 7, because it is correct for MST Mountain Standard Time. If we are using an ephemeris to make corrections we will need to note the minute calculations for corrections. If we are using a program to correct, then altering the time zone should be sufficient, especially since the longitude and latitude are already configured in the chart calculations.
What is important is knowing when daylight savings time begins and ends. When we construct charts for people that may have been born when daylight savings time was not being observed, or after a country or providence decided to no longer observe daylight savings time we need to be aware, so that we can construct an accurate chart.