Today I will explain about how to convert date from solar to lunar (Hijri) Using VB.NET The Lunar (Hijri) calendar is very important for Muslims as is the Solar calendar is important because the Lunar calendar was related to some elements of worship, so I looked at many sites on the internet to understand how to calculate the age of the moon in any given day, I found many sites offering various ways and I took what I found to provide results closer to the truth.

I’ve noticed that most sites agree on the expense of the date but don’t agree on how to calculate the age of the moon and found the difference between these sites to be up to one day and when the moon’s age is 30 days, the result is zero in some sites.
In this program I calculate the approximate age of the moon in days and did not give attention to the parts of the day of the hours and minutes.

For the program to be more useful, I added a PictureBox control to display the lighted part of the moon and darkness part of the moon commensurate with the age of the moon.
There is a small probability of a one-day error for any calculation to convert a date.

Note: You can read Months by its name or by its number.

Code

Best Calculation to Get Number Approximation

Private Function getInt(ByRef fNumber As Double) As Double  
    If fNumber < -0.0000001 Then  
        getInt = Math.Ceiling(fNumber - 0.0000001)  
    Else  
        getInt = Math.Floor(fNumber + 0.0000001)  
    End If  
End Function

 Convert Solar Date to Lunar (Hijri) Date 

Private Sub SolarToLunar()  
    ' convert Solar year from 622 to 2500  
    Dim jd As Double  
    Dim j, L, n As Double  
    Dim d, m, y As Integer  
    Dim theDay As Integer  
    ' Solar day  
    d = Val(SolarDay.Text)  
    'get the number of Solar month  
    m = SolarMonth.SelectedIndex + 1  
    ' Solar year  
    y = Val(SolarYear.Text)  
    If (y > 1582) Or ((y = 1582) And (m > 10)) Or ((y = 1582) And (m = 10) And (d > 14)) Then  
            jd = getInt((1461 * (y + 4800 + getInt((m - 14) / 12))) / 4) + getInt((367 * (m - 2 - 12 * (getInt((m - 14) / 12)))) / 12) - getInt((3 * (getInt((y + 4900 + getInt((m - 14) / 12)) / 100))) / 4) + d - 32075  
        Else  
            jd = 367 * y - getInt((7 * (y + 5001 + getInt((m - 9) / 7))) / 4) + getInt((275 * m) / 9) + d + 1729777  
        End If  
        ' Solar year >= 622  
        If jd < 1948440 Then  
            DateMinError()  
            Exit Sub  
        End If  
        ' Solar year <= 2500  
        If jd > 2621734 Then  
            DateMaxError()  
            Exit Sub  
        End If  
        'day of the week  
        theDay = jd Mod 7  
        lblDay.Text = WeekDays(theDay)  
        L = jd - 1948440 + 10632  
        n = getInt((L - 1) / 10631)  
        L = L - 10631 * n + 354  
        j = (getInt((10985 - L) / 5316)) * (getInt((50 * L) / 17719)) + (getInt(L / 5670)) * (getInt((43 * L) / 15238))  
        L = L - (getInt((30 - j) / 15)) * (getInt((17719 * j) / 50)) - (getInt(j / 16)) * (getInt((15238 * j) / 43)) + 29  
        m = Int(getInt((24 * L) / 709))  
        d = Int(L - getInt((709 * m) / 24))  
        y = Int(30 * n + j - 30)  
        ' display Lunar date  
        LunarDay.Text = Str(d)  
        LunarMonth.Text = LunarMonths(m - 1)  
        LunarYear.Text = Str(y)  
        ShowMoonPhase()  
    If d = 1 Then  
        lblAge.Text = Str(d) & " day"  
    Else  
        lblAge.Text = Str(d) & " days"  
    End If  
End Sub  

 Convert Lunar (Hijri) Date to Solar Date

Private Sub LunarToSolar()  
    ' convert Lunar year from 1 to 1900  
    Dim jd As Double  
    Dim i, j, k, L, n As Double  
    Dim d, m, y As Integer  
    Dim theDay As Integer  
    ' Lunar day  
    d = Val(LunarDay.Text)  
    If d = 1 Then  
        lblAge.Text = Str(d) & " day"  
    Else  
        lblAge.Text = Str(d) & " days"  
    End If  
    'get the number of Lunar month  
    m = LunarMonth.SelectedIndex + 1  
    ' Lunar year  
    y = Val(LunarYear.Text)  
    jd = getInt((11 * y + 3) / 30) + 354 * y + 30 * m - getInt((m - 1) / 2) + d + 1948440 - 385  
    'day of the week  
    theDay = jd Mod 7  
    lblDay.Text = WeekDays(theDay)  
    If jd > 2299160 Then  
        L = jd + 68569  
        n = getInt((4 * L) / 146097)  
        L = L - getInt((146097 * n + 3) / 4)  
        i = getInt((4000 * (L + 1)) / 1461001)  
        L = L - getInt((1461 * i) / 4) + 31  
        j = getInt((80 * L) / 2447)  
        d = Int(L - getInt((2447 * j) / 80))  
        L = getInt(j / 11)  
        m = Int(j + 2 - 12 * L)  
        y = Int(100 * (n - 49) + i + L)  
    Else  
        j = jd + 1402  
        k = getInt((j - 1) / 1461)  
        L = j - 1461 * k  
        n = getInt((L - 1) / 365) - getInt(L / 1461)  
        i = L - 365 * n + 30  
        j = getInt((80 * i) / 2447)  
        d = Int(i - getInt((2447 * j) / 80))  
    i = getInt(j / 11)  
        m = Int(j + 2 - 12 * i)  
        y = Int(4 * k + n + i - 4716)  
    End If  
    ' display Solar date  
    SolarDay.Text = Str(d)  
    SolarMonth.Text = SolarMonths(m - 1)  
    SolarYear.Text = Str(y)  
    ShowMoonPhase()  
End Sub  

 Draw the Moon at Selected Date

Private Sub ShowMoonPhase()  
    Dim ag As Integer = Val(LunarDay.Text)  
    Dim Phase As Double = ag / 29.530588853  
    Dim Xpos, Ypos, Rpos As Integer  
    Dim Xpos1, Xpos2 As Integer  
    Me.ClearDraw() 'clear PicMoon PictureBox  
    ' Width of 'ImageToDraw' Object = Width of 'PicMoon' control  
    Dim PageWidth As Integer = Me.MoonShape.Width  
    ' Height of 'ImageToDraw' Object = Height of 'PicMoon' control  
    Dim PageHeight As Integer = Me.MoonShape.Height  
    ' Initiate 'ImageToDraw' Object with size = size of control 'PicMoon' control  
    Dim ImageToDraw As Bitmap = New Bitmap(PageWidth, PageHeight)  
    'Create graphics object for alteration.  
    Dim newGraphics As Graphics = Graphics.FromImage(ImageToDraw)  
    Dim PenW As Pen = New Pen(Color.White) ' For lighted part of the moon  
    Dim PenB As Pen = New Pen(Color.Black) ' For darkness part of the moon  
    For Ypos = 0 To 45  
        Xpos = Int(Math.Sqrt(45 * 45 - Ypos * Ypos))  
        ' Draw darkness part of the moon  
        Dim pB1 As Point = New Point(90 - Xpos, Ypos + 90)  
        Dim pB2 As Point = New Point(Xpos + 90, Ypos + 90)  
        Dim pB3 As Point = New Point(90 - Xpos, 90 - Ypos)  
        Dim pB4 As Point = New Point(Xpos + 90, 90 - Ypos)  
        newGraphics.DrawLine(PenW, pB1, pB2)  
        newGraphics.DrawLine(PenW, pB3, pB4)  
        ' Determine the edges of the lighted part of the moon  
        Rpos = 2 * Xpos  
        If (Phase < 0.5) Then  
            Xpos1 = -Xpos  
            Xpos2 = Int(Rpos - 2 * Phase * Rpos - Xpos)  
        Else  
            Xpos1 = Xpos  
            Xpos2 = Int(Xpos - 2 * Phase * Rpos + Rpos)  
        End If  
        ' Draw the lighted part of the moon  
        Dim pW1 As Point = New Point(Xpos1 + 90, 90 - Ypos)  
        Dim pW2 As Point = New Point(Xpos2 + 90, 90 - Ypos)  
        Dim pW3 As Point = New Point(Xpos1 + 90, Ypos + 90)  
        Dim pW4 As Point = New Point(Xpos2 + 90, Ypos + 90)  
        newGraphics.DrawLine(PenB, pW1, pW2)  
        newGraphics.DrawLine(PenB, pW3, pW4)  
    Next  
    ' Display the bitmap in the picture box.  
    Me.MoonShape.Image = ImageToDraw  
    ' Release graphics object  
    PenW.Dispose()  
    PenB.Dispose()  
    newGraphics.Dispose()  
    ImageToDraw = Nothing  
End Sub